shithub: hugo

Download patch

ref: f9978ed16476ca6d233a89669c62c798cdf9db9d
parent: 58d4c0a8be8beefbd7437b17bf7a9a381164d09b
author: Bjørn Erik Pedersen <bjorn.erik.pedersen@gmail.com>
date: Sun Aug 18 07:21:27 EDT 2019 

Image resource refactor

This commit pulls most of the image related logic into its own package, to make it easier to reason about and extend.

This is also a rewrite of the transformation logic used in Hugo Pipes, mostly to allow constructs like the one below:

    {{ ($myimg | fingerprint ).Width }}

Fixes #5903
Fixes #6234
Fixes #6266

diff: cannot open b/hugolib/assets/images//null: file does not exist: 'b/hugolib/assets/images//null' diff: cannot open b/hugolib/assets//null: file does not exist: 'b/hugolib/assets//null' diff: cannot open b/resources/images//null: file does not exist: 'b/resources/images//null' diff: cannot open b/resources/internal//null: file does not exist: 'b/resources/internal//null' diff: cannot open b/resources/resource_transformers/htesting//null: file does not exist: 'b/resources/resource_transformers/htesting//null' 
--- a/common/herrors/errors.go
+++ b/common/herrors/errors.go
@@ -52,6 +52,7 @@
 //     defer herrors.Recover()
 func Recover(args ...interface{}) {
 	if r := recover(); r != nil {
+		fmt.Println("ERR:", r)
 		args = append(args, "stacktrace from panic: \n"+string(debug.Stack()), "\n")
 		fmt.Println(args...)
 	}
--- a/htesting/test_helpers.go
+++ b/htesting/test_helpers.go
@@ -14,8 +14,10 @@
 package htesting
 
 import (
+	"math/rand"
 	"runtime"
 	"strings"
+	"time"
 
 	"github.com/spf13/afero"
 )
@@ -36,4 +38,21 @@
 		tempDir = "/private" + tempDir
 	}
 	return tempDir, func() { fs.RemoveAll(tempDir) }, nil
+}
+
+// BailOut panics with a stack trace after the given duration. Useful for
+// hanging tests.
+func BailOut(after time.Duration) {
+	time.AfterFunc(after, func() {
+		buf := make([]byte, 1<<16)
+		runtime.Stack(buf, true)
+		panic(string(buf))
+	})
+
+}
+
+var rnd = rand.New(rand.NewSource(time.Now().UnixNano()))
+
+func RandIntn(n int) int {
+	return rnd.Intn(n)
 }
binary files /dev/null b/hugolib/assets/images/sunset.jpg differ
--- a/hugolib/pagebundler_test.go
+++ b/hugolib/pagebundler_test.go
@@ -42,8 +42,7 @@
 )
 
 func TestPageBundlerSiteRegular(t *testing.T) {
-	t.Parallel()
-
+	c := qt.New(t)
 	baseBaseURL := "https://example.com"
 
 	for _, baseURLPath := range []string{"", "/hugo"} {
@@ -55,15 +54,14 @@
 				}
 				ugly := ugly
 				canonify := canonify
-				t.Run(fmt.Sprintf("ugly=%t,canonify=%t,path=%s", ugly, canonify, baseURLPathId),
-					func(t *testing.T) {
-						t.Parallel()
+				c.Run(fmt.Sprintf("ugly=%t,canonify=%t,path=%s", ugly, canonify, baseURLPathId),
+					func(c *qt.C) {
+						c.Parallel()
 						baseURL := baseBaseURL + baseURLPath
 						relURLBase := baseURLPath
 						if canonify {
 							relURLBase = ""
 						}
-						c := qt.New(t)
 						fs, cfg := newTestBundleSources(t)
 						cfg.Set("baseURL", baseURL)
 						cfg.Set("canonifyURLs", canonify)
--- a/hugolib/resource_chain_test.go
+++ b/hugolib/resource_chain_test.go
@@ -14,6 +14,7 @@
 package hugolib
 
 import (
+	"io"
 	"os"
 	"path/filepath"
 	"testing"
@@ -167,6 +168,64 @@
 
 }
 
+func TestResourceChainBasic(t *testing.T) {
+	t.Parallel()
+
+	b := newTestSitesBuilder(t)
+	b.WithTemplatesAdded("index.html", `
+{{ $hello := "<h1>     Hello World!   </h1>" | resources.FromString "hello.html" | fingerprint "sha512" | minify  | fingerprint }}
+
+HELLO: {{ $hello.Name }}|{{ $hello.RelPermalink }}|{{ $hello.Content | safeHTML }}
+
+{{ $img := resources.Get "images/sunset.jpg" }}
+{{ $fit := $img.Fit "200x200" }}
+{{ $fit2 := $fit.Fit "100x200" }}
+{{ $img = $img | fingerprint }}
+SUNSET: {{ $img.Name }}|{{ $img.RelPermalink }}|{{ $img.Width }}|{{ len $img.Content }}
+FIT: {{ $fit.Name }}|{{ $fit.RelPermalink }}|{{ $fit.Width }}
+`)
+
+	fs := b.Fs.Source
+
+	imageDir := filepath.Join("assets", "images")
+	b.Assert(os.MkdirAll(imageDir, 0777), qt.IsNil)
+	src, err := os.Open("testdata/sunset.jpg")
+	b.Assert(err, qt.IsNil)
+	out, err := fs.Create(filepath.Join(imageDir, "sunset.jpg"))
+	b.Assert(err, qt.IsNil)
+	_, err = io.Copy(out, src)
+	b.Assert(err, qt.IsNil)
+	out.Close()
+
+	b.Running()
+
+	for i := 0; i < 2; i++ {
+
+		b.Build(BuildCfg{})
+
+		b.AssertFileContent("public/index.html",
+			`
+SUNSET: images/sunset.jpg|/images/sunset.a9bf1d944e19c0f382e0d8f51de690f7d0bc8fa97390c4242a86c3e5c0737e71.jpg|900|90587
+FIT: images/sunset.jpg|/images/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_200x200_fit_q75_box.jpg|200
+
+`)
+
+		b.EditFiles("page1.md", `
+---
+title: "Page 1 edit"
+summary: "Edited summary"
+---
+
+Edited content.
+
+`)
+
+		b.Assert(b.Fs.Destination.Remove("public"), qt.IsNil)
+		b.H.ResourceSpec.ClearCaches()
+
+	}
+}
+
 func TestResourceChain(t *testing.T) {
 	t.Parallel()
 
@@ -353,9 +412,11 @@
 				"Publish 1: body{color:blue} /external1.min.css",
 				"Publish 2: http://example.com/external2.min.css",
 			)
-			c.Assert(b.CheckExists("public/external2.min.css"), qt.Equals, true)
-			c.Assert(b.CheckExists("public/external1.min.css"), qt.Equals, true)
-			c.Assert(b.CheckExists("public/inline.min.css"), qt.Equals, false)
+			b.Assert(b.CheckExists("public/external2.css"), qt.Equals, false)
+			b.Assert(b.CheckExists("public/external1.css"), qt.Equals, false)
+			b.Assert(b.CheckExists("public/external2.min.css"), qt.Equals, true)
+			b.Assert(b.CheckExists("public/external1.min.css"), qt.Equals, true)
+			b.Assert(b.CheckExists("public/inline.min.css"), qt.Equals, false)
 		}},
 
 		{"unmarshal", func() bool { return true }, func(b *sitesBuilder) {
--- a/hugolib/testhelpers_test.go
+++ b/hugolib/testhelpers_test.go
@@ -536,6 +536,7 @@
 }
 
 func (s *sitesBuilder) build(cfg BuildCfg, shouldFail bool) *sitesBuilder {
+	s.Helper()
 	defer func() {
 		s.changedFiles = nil
 	}()
--- a/resources/image.go
+++ b/resources/image.go
@@ -14,17 +14,14 @@
 package resources
 
 import (
-	"errors"
 	"fmt"
 	"image"
 	"image/color"
 	"image/draw"
-	"image/jpeg"
-	"io"
+	_ "image/gif"
+	_ "image/png"
 	"os"
-	"strconv"
 	"strings"
-	"sync"
 
 	"github.com/gohugoio/hugo/resources/resource"
 
@@ -31,13 +28,10 @@
 	_errors "github.com/pkg/errors"
 
 	"github.com/disintegration/imaging"
-	"github.com/gohugoio/hugo/common/hugio"
 	"github.com/gohugoio/hugo/helpers"
-	"github.com/mitchellh/mapstructure"
+	"github.com/gohugoio/hugo/resources/images"
 
 	// Blind import for image.Decode
-	_ "image/gif"
-	_ "image/png"
 
 	// Blind import for image.Decode
 	_ "golang.org/x/image/webp"
@@ -44,128 +38,60 @@
 )
 
 var (
-	_ resource.Resource = (*Image)(nil)
-	_ resource.Source   = (*Image)(nil)
-	_ resource.Cloner   = (*Image)(nil)
+	_ resource.Image  = (*imageResource)(nil)
+	_ resource.Source = (*imageResource)(nil)
+	_ resource.Cloner = (*imageResource)(nil)
 )
 
-// Imaging contains default image processing configuration. This will be fetched
-// from site (or language) config.
-type Imaging struct {
-	// Default image quality setting (1-100). Only used for JPEG images.
-	Quality int
+// ImageResource represents an image resource.
+type imageResource struct {
+	*images.Image
 
-	// Resample filter used. See https://github.com/disintegration/imaging
-	ResampleFilter string
-
-	// The anchor used in Fill. Default is "smart", i.e. Smart Crop.
-	Anchor string
+	baseResource
 }
 
-const (
-	defaultJPEGQuality    = 75
-	defaultResampleFilter = "box"
-)
-
-var (
-	imageFormats = map[string]imaging.Format{
-		".jpg":  imaging.JPEG,
-		".jpeg": imaging.JPEG,
-		".png":  imaging.PNG,
-		".tif":  imaging.TIFF,
-		".tiff": imaging.TIFF,
-		".bmp":  imaging.BMP,
-		".gif":  imaging.GIF,
+func (i *imageResource) Clone() resource.Resource {
+	gr := i.baseResource.Clone().(baseResource)
+	return &imageResource{
+		Image:        i.WithSpec(gr),
+		baseResource: gr,
 	}
+}
 
-	// Add or increment if changes to an image format's processing requires
-	// re-generation.
-	imageFormatsVersions = map[imaging.Format]int{
-		imaging.PNG: 2, // Floyd Steinberg dithering
+func (i *imageResource) cloneWithUpdates(u *transformationUpdate) (baseResource, error) {
+	base, err := i.baseResource.cloneWithUpdates(u)
+	if err != nil {
+		return nil, err
 	}
 
-	// Increment to mark all processed images as stale. Only use when absolutely needed.
-	// See the finer grained smartCropVersionNumber and imageFormatsVersions.
-	mainImageVersionNumber = 0
-)
+	var img *images.Image
 
-var anchorPositions = map[string]imaging.Anchor{
-	strings.ToLower("Center"):      imaging.Center,
-	strings.ToLower("TopLeft"):     imaging.TopLeft,
-	strings.ToLower("Top"):         imaging.Top,
-	strings.ToLower("TopRight"):    imaging.TopRight,
-	strings.ToLower("Left"):        imaging.Left,
-	strings.ToLower("Right"):       imaging.Right,
-	strings.ToLower("BottomLeft"):  imaging.BottomLeft,
-	strings.ToLower("Bottom"):      imaging.Bottom,
-	strings.ToLower("BottomRight"): imaging.BottomRight,
-}
+	if u.isContenChanged() {
+		img = i.WithSpec(base)
+	} else {
+		img = i.Image
+	}
 
-var imageFilters = map[string]imaging.ResampleFilter{
-	strings.ToLower("NearestNeighbor"):   imaging.NearestNeighbor,
-	strings.ToLower("Box"):               imaging.Box,
-	strings.ToLower("Linear"):            imaging.Linear,
-	strings.ToLower("Hermite"):           imaging.Hermite,
-	strings.ToLower("MitchellNetravali"): imaging.MitchellNetravali,
-	strings.ToLower("CatmullRom"):        imaging.CatmullRom,
-	strings.ToLower("BSpline"):           imaging.BSpline,
-	strings.ToLower("Gaussian"):          imaging.Gaussian,
-	strings.ToLower("Lanczos"):           imaging.Lanczos,
-	strings.ToLower("Hann"):              imaging.Hann,
-	strings.ToLower("Hamming"):           imaging.Hamming,
-	strings.ToLower("Blackman"):          imaging.Blackman,
-	strings.ToLower("Bartlett"):          imaging.Bartlett,
-	strings.ToLower("Welch"):             imaging.Welch,
-	strings.ToLower("Cosine"):            imaging.Cosine,
+	return &imageResource{
+		Image:        img,
+		baseResource: base,
+	}, nil
 }
 
-// Image represents an image resource.
-type Image struct {
-	config       image.Config
-	configInit   sync.Once
-	configLoaded bool
-
-	imaging *Imaging
-
-	format imaging.Format
-
-	*genericResource
-}
-
-// Width returns i's width.
-func (i *Image) Width() int {
-	i.initConfig()
-	return i.config.Width
-}
-
-// Height returns i's height.
-func (i *Image) Height() int {
-	i.initConfig()
-	return i.config.Height
-}
-
-// WithNewBase implements the Cloner interface.
-func (i *Image) WithNewBase(base string) resource.Resource {
-	return &Image{
-		imaging:         i.imaging,
-		format:          i.format,
-		genericResource: i.genericResource.WithNewBase(base).(*genericResource)}
-}
-
 // Resize resizes the image to the specified width and height using the specified resampling
 // filter and returns the transformed image. If one of width or height is 0, the image aspect
 // ratio is preserved.
-func (i *Image) Resize(spec string) (*Image, error) {
-	return i.doWithImageConfig("resize", spec, func(src image.Image, conf imageConfig) (image.Image, error) {
-		return imaging.Resize(src, conf.Width, conf.Height, conf.Filter), nil
+func (i *imageResource) Resize(spec string) (resource.Image, error) {
+	return i.doWithImageConfig("resize", spec, func(src image.Image, conf images.ImageConfig) (image.Image, error) {
+		return i.Proc.Resize(src, conf)
 	})
 }
 
 // Fit scales down the image using the specified resample filter to fit the specified
 // maximum width and height.
-func (i *Image) Fit(spec string) (*Image, error) {
-	return i.doWithImageConfig("fit", spec, func(src image.Image, conf imageConfig) (image.Image, error) {
-		return imaging.Fit(src, conf.Width, conf.Height, conf.Filter), nil
+func (i *imageResource) Fit(spec string) (resource.Image, error) {
+	return i.doWithImageConfig("fit", spec, func(src image.Image, conf images.ImageConfig) (image.Image, error) {
+		return i.Proc.Fit(src, conf)
 	})
 }
 
@@ -172,40 +98,14 @@
 // Fill scales the image to the smallest possible size that will cover the specified dimensions,
 // crops the resized image to the specified dimensions using the given anchor point.
 // Space delimited config: 200x300 TopLeft
-func (i *Image) Fill(spec string) (*Image, error) {
-	return i.doWithImageConfig("fill", spec, func(src image.Image, conf imageConfig) (image.Image, error) {
-		if conf.AnchorStr == smartCropIdentifier {
-			return smartCrop(src, conf.Width, conf.Height, conf.Anchor, conf.Filter)
-		}
-		return imaging.Fill(src, conf.Width, conf.Height, conf.Anchor, conf.Filter), nil
+func (i *imageResource) Fill(spec string) (resource.Image, error) {
+	return i.doWithImageConfig("fill", spec, func(src image.Image, conf images.ImageConfig) (image.Image, error) {
+		return i.Proc.Fill(src, conf)
 	})
 }
 
-// Holds configuration to create a new image from an existing one, resize etc.
-type imageConfig struct {
-	Action string
-
-	// Quality ranges from 1 to 100 inclusive, higher is better.
-	// This is only relevant for JPEG images.
-	// Default is 75.
-	Quality int
-
-	// Rotate rotates an image by the given angle counter-clockwise.
-	// The rotation will be performed first.
-	Rotate int
-
-	Width  int
-	Height int
-
-	Filter    imaging.ResampleFilter
-	FilterStr string
-
-	Anchor    imaging.Anchor
-	AnchorStr string
-}
-
-func (i *Image) isJPEG() bool {
-	name := strings.ToLower(i.relTargetDirFile.file)
+func (i *imageResource) isJPEG() bool {
+	name := strings.ToLower(i.getResourcePaths().relTargetDirFile.file)
 	return strings.HasSuffix(name, ".jpg") || strings.HasSuffix(name, ".jpeg")
 }
 
@@ -218,43 +118,21 @@
 
 var imageProcSem = make(chan bool, imageProcWorkers)
 
-func (i *Image) doWithImageConfig(action, spec string, f func(src image.Image, conf imageConfig) (image.Image, error)) (*Image, error) {
-	conf, err := parseImageConfig(spec)
+func (i *imageResource) doWithImageConfig(action, spec string, f func(src image.Image, conf images.ImageConfig) (image.Image, error)) (resource.Image, error) {
+	conf, err := i.decodeImageConfig(action, spec)
 	if err != nil {
 		return nil, err
 	}
-	conf.Action = action
 
-	if conf.Quality <= 0 && i.isJPEG() {
-		// We need a quality setting for all JPEGs
-		conf.Quality = i.imaging.Quality
-	}
-
-	if conf.FilterStr == "" {
-		conf.FilterStr = i.imaging.ResampleFilter
-		conf.Filter = imageFilters[conf.FilterStr]
-	}
-
-	if conf.AnchorStr == "" {
-		conf.AnchorStr = i.imaging.Anchor
-		if !strings.EqualFold(conf.AnchorStr, smartCropIdentifier) {
-			conf.Anchor = anchorPositions[conf.AnchorStr]
-		}
-	}
-
-	return i.spec.imageCache.getOrCreate(i, conf, func() (*Image, image.Image, error) {
+	return i.getSpec().imageCache.getOrCreate(i, conf, func() (*imageResource, image.Image, error) {
 		imageProcSem <- true
 		defer func() {
 			<-imageProcSem
 		}()
 
-		ci := i.clone()
-
 		errOp := action
-		errPath := i.sourceFilename
+		errPath := i.getSourceFilename()
 
-		ci.setBasePath(conf)
-
 		src, err := i.decodeSource()
 		if err != nil {
 			return nil, nil, &os.PathError{Op: errOp, Path: errPath, Err: err}
@@ -267,10 +145,10 @@
 
 		converted, err := f(src, conf)
 		if err != nil {
-			return ci, nil, &os.PathError{Op: errOp, Path: errPath, Err: err}
+			return nil, nil, &os.PathError{Op: errOp, Path: errPath, Err: err}
 		}
 
-		if i.format == imaging.PNG {
+		if i.Format == imaging.PNG {
 			// Apply the colour palette from the source
 			if paletted, ok := src.(*image.Paletted); ok {
 				tmp := image.NewPaletted(converted.Bounds(), paletted.Palette)
@@ -279,177 +157,30 @@
 			}
 		}
 
-		b := converted.Bounds()
-		ci.config = image.Config{Width: b.Max.X, Height: b.Max.Y}
-		ci.configLoaded = true
+		ci := i.clone(converted)
+		ci.setBasePath(conf)
 
 		return ci, converted, nil
 	})
-
 }
 
-func (i imageConfig) key(format imaging.Format) string {
-	k := strconv.Itoa(i.Width) + "x" + strconv.Itoa(i.Height)
-	if i.Action != "" {
-		k += "_" + i.Action
+func (i *imageResource) decodeImageConfig(action, spec string) (images.ImageConfig, error) {
+	conf, err := images.DecodeImageConfig(action, spec, i.Proc.Cfg)
+	if err != nil {
+		return conf, err
 	}
-	if i.Quality > 0 {
-		k += "_q" + strconv.Itoa(i.Quality)
-	}
-	if i.Rotate != 0 {
-		k += "_r" + strconv.Itoa(i.Rotate)
-	}
-	anchor := i.AnchorStr
-	if anchor == smartCropIdentifier {
-		anchor = anchor + strconv.Itoa(smartCropVersionNumber)
-	}
 
-	k += "_" + i.FilterStr
+	iconf := i.Proc.Cfg
 
-	if strings.EqualFold(i.Action, "fill") {
-		k += "_" + anchor
+	if conf.Quality <= 0 && i.isJPEG() {
+		// We need a quality setting for all JPEGs
+		conf.Quality = iconf.Quality
 	}
 
-	if v, ok := imageFormatsVersions[format]; ok {
-		k += "_" + strconv.Itoa(v)
-	}
-
-	if mainImageVersionNumber > 0 {
-		k += "_" + strconv.Itoa(mainImageVersionNumber)
-	}
-
-	return k
+	return conf, nil
 }
 
-func newImageConfig(width, height, quality, rotate int, filter, anchor string) imageConfig {
-	var c imageConfig
-
-	c.Width = width
-	c.Height = height
-	c.Quality = quality
-	c.Rotate = rotate
-
-	if filter != "" {
-		filter = strings.ToLower(filter)
-		if v, ok := imageFilters[filter]; ok {
-			c.Filter = v
-			c.FilterStr = filter
-		}
-	}
-
-	if anchor != "" {
-		anchor = strings.ToLower(anchor)
-		if v, ok := anchorPositions[anchor]; ok {
-			c.Anchor = v
-			c.AnchorStr = anchor
-		}
-	}
-
-	return c
-}
-
-func parseImageConfig(config string) (imageConfig, error) {
-	var (
-		c   imageConfig
-		err error
-	)
-
-	if config == "" {
-		return c, errors.New("image config cannot be empty")
-	}
-
-	parts := strings.Fields(config)
-	for _, part := range parts {
-		part = strings.ToLower(part)
-
-		if part == smartCropIdentifier {
-			c.AnchorStr = smartCropIdentifier
-		} else if pos, ok := anchorPositions[part]; ok {
-			c.Anchor = pos
-			c.AnchorStr = part
-		} else if filter, ok := imageFilters[part]; ok {
-			c.Filter = filter
-			c.FilterStr = part
-		} else if part[0] == 'q' {
-			c.Quality, err = strconv.Atoi(part[1:])
-			if err != nil {
-				return c, err
-			}
-			if c.Quality < 1 || c.Quality > 100 {
-				return c, errors.New("quality ranges from 1 to 100 inclusive")
-			}
-		} else if part[0] == 'r' {
-			c.Rotate, err = strconv.Atoi(part[1:])
-			if err != nil {
-				return c, err
-			}
-		} else if strings.Contains(part, "x") {
-			widthHeight := strings.Split(part, "x")
-			if len(widthHeight) <= 2 {
-				first := widthHeight[0]
-				if first != "" {
-					c.Width, err = strconv.Atoi(first)
-					if err != nil {
-						return c, err
-					}
-				}
-
-				if len(widthHeight) == 2 {
-					second := widthHeight[1]
-					if second != "" {
-						c.Height, err = strconv.Atoi(second)
-						if err != nil {
-							return c, err
-						}
-					}
-				}
-			} else {
-				return c, errors.New("invalid image dimensions")
-			}
-
-		}
-	}
-
-	if c.Width == 0 && c.Height == 0 {
-		return c, errors.New("must provide Width or Height")
-	}
-
-	return c, nil
-}
-
-func (i *Image) initConfig() error {
-	var err error
-	i.configInit.Do(func() {
-		if i.configLoaded {
-			return
-		}
-
-		var (
-			f      hugio.ReadSeekCloser
-			config image.Config
-		)
-
-		f, err = i.ReadSeekCloser()
-		if err != nil {
-			return
-		}
-		defer f.Close()
-
-		config, _, err = image.DecodeConfig(f)
-		if err != nil {
-			return
-		}
-		i.config = config
-	})
-
-	if err != nil {
-		return _errors.Wrap(err, "failed to load image config")
-	}
-
-	return nil
-}
-
-func (i *Image) decodeSource() (image.Image, error) {
+func (i *imageResource) decodeSource() (image.Image, error) {
 	f, err := i.ReadSeekCloser()
 	if err != nil {
 		return nil, _errors.Wrap(err, "failed to open image for decode")
@@ -459,80 +190,39 @@
 	return img, err
 }
 
-// returns an opened file or nil if nothing to write.
-func (i *Image) openDestinationsForWriting() (io.WriteCloser, error) {
-	targetFilenames := i.targetFilenames()
-	var changedFilenames []string
+func (i *imageResource) clone(img image.Image) *imageResource {
+	spec := i.baseResource.Clone().(baseResource)
 
-	// Fast path:
-	// This is a processed version of the original;
-	// check if it already existis at the destination.
-	for _, targetFilename := range targetFilenames {
-		if _, err := i.spec.BaseFs.PublishFs.Stat(targetFilename); err == nil {
-			continue
-		}
-		changedFilenames = append(changedFilenames, targetFilename)
+	var image *images.Image
+	if img != nil {
+		image = i.WithImage(img)
+	} else {
+		image = i.WithSpec(spec)
 	}
 
-	if len(changedFilenames) == 0 {
-		return nil, nil
+	return &imageResource{
+		Image:        image,
+		baseResource: spec,
 	}
-
-	return helpers.OpenFilesForWriting(i.spec.BaseFs.PublishFs, changedFilenames...)
-
 }
 
-func (i *Image) encodeTo(conf imageConfig, img image.Image, w io.Writer) error {
-	switch i.format {
-	case imaging.JPEG:
-
-		var rgba *image.RGBA
-		quality := conf.Quality
-
-		if nrgba, ok := img.(*image.NRGBA); ok {
-			if nrgba.Opaque() {
-				rgba = &image.RGBA{
-					Pix:    nrgba.Pix,
-					Stride: nrgba.Stride,
-					Rect:   nrgba.Rect,
-				}
-			}
-		}
-		if rgba != nil {
-			return jpeg.Encode(w, rgba, &jpeg.Options{Quality: quality})
-		}
-		return jpeg.Encode(w, img, &jpeg.Options{Quality: quality})
-	default:
-		return imaging.Encode(w, img, i.format)
-	}
+func (i *imageResource) setBasePath(conf images.ImageConfig) {
+	i.getResourcePaths().relTargetDirFile = i.relTargetPathFromConfig(conf)
 }
 
-func (i *Image) clone() *Image {
-	g := *i.genericResource
-	g.resourceContent = &resourceContent{}
-	if g.publishOnce != nil {
-		g.publishOnce = &publishOnce{logger: g.publishOnce.logger}
+func (i *imageResource) relTargetPathFromConfig(conf images.ImageConfig) dirFile {
+	p1, p2 := helpers.FileAndExt(i.getResourcePaths().relTargetDirFile.file)
+	if conf.Action == "trace" {
+		p2 = ".svg"
 	}
 
-	return &Image{
-		imaging:         i.imaging,
-		format:          i.format,
-		genericResource: &g}
-}
+	h, _ := i.hash()
+	idStr := fmt.Sprintf("_hu%s_%d", h, i.size())
 
-func (i *Image) setBasePath(conf imageConfig) {
-	i.relTargetDirFile = i.relTargetPathFromConfig(conf)
-}
-
-func (i *Image) relTargetPathFromConfig(conf imageConfig) dirFile {
-	p1, p2 := helpers.FileAndExt(i.relTargetDirFile.file)
-
-	idStr := fmt.Sprintf("_hu%s_%d", i.hash, i.osFileInfo.Size())
-
 	// Do not change for no good reason.
 	const md5Threshold = 100
 
-	key := conf.key(i.format)
+	key := conf.Key(i.Format)
 
 	// It is useful to have the key in clear text, but when nesting transforms, it
 	// can easily be too long to read, and maybe even too long
@@ -554,43 +244,7 @@
 	}
 
 	return dirFile{
-		dir:  i.relTargetDirFile.dir,
+		dir:  i.getResourcePaths().relTargetDirFile.dir,
 		file: fmt.Sprintf("%s%s_%s%s", p1, idStr, key, p2),
 	}
-
-}
-
-func decodeImaging(m map[string]interface{}) (Imaging, error) {
-	var i Imaging
-	if err := mapstructure.WeakDecode(m, &i); err != nil {
-		return i, err
-	}
-
-	if i.Quality == 0 {
-		i.Quality = defaultJPEGQuality
-	} else if i.Quality < 0 || i.Quality > 100 {
-		return i, errors.New("JPEG quality must be a number between 1 and 100")
-	}
-
-	if i.Anchor == "" || strings.EqualFold(i.Anchor, smartCropIdentifier) {
-		i.Anchor = smartCropIdentifier
-	} else {
-		i.Anchor = strings.ToLower(i.Anchor)
-		if _, found := anchorPositions[i.Anchor]; !found {
-			return i, errors.New("invalid anchor value in imaging config")
-		}
-	}
-
-	if i.ResampleFilter == "" {
-		i.ResampleFilter = defaultResampleFilter
-	} else {
-		filter := strings.ToLower(i.ResampleFilter)
-		_, found := imageFilters[filter]
-		if !found {
-			return i, fmt.Errorf("%q is not a valid resample filter", filter)
-		}
-		i.ResampleFilter = filter
-	}
-
-	return i, nil
 }
--- a/resources/image_cache.go
+++ b/resources/image_cache.go
@@ -20,7 +20,7 @@
 	"strings"
 	"sync"
 
-	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/resources/images"
 
 	"github.com/gohugoio/hugo/cache/filecache"
 	"github.com/gohugoio/hugo/helpers"
@@ -32,7 +32,7 @@
 	fileCache *filecache.Cache
 
 	mu    sync.RWMutex
-	store map[string]*Image
+	store map[string]*resourceAdapter
 }
 
 func (c *imageCache) isInCache(key string) bool {
@@ -66,33 +66,34 @@
 func (c *imageCache) clear() {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	c.store = make(map[string]*Image)
+	c.store = make(map[string]*resourceAdapter)
 }
 
 func (c *imageCache) getOrCreate(
-	parent *Image, conf imageConfig, createImage func() (*Image, image.Image, error)) (*Image, error) {
-
+	parent *imageResource, conf images.ImageConfig,
+	createImage func() (*imageResource, image.Image, error)) (*resourceAdapter, error) {
 	relTarget := parent.relTargetPathFromConfig(conf)
 	key := parent.relTargetPathForRel(relTarget.path(), false, false, false)
 
 	// First check the in-memory store, then the disk.
 	c.mu.RLock()
-	img, found := c.store[key]
+	cachedImage, found := c.store[key]
 	c.mu.RUnlock()
 
 	if found {
-		return img, nil
+		return cachedImage, nil
 	}
 
+	var img *imageResource
+
 	// These funcs are protected by a named lock.
 	// read clones the parent to its new name and copies
 	// the content to the destinations.
 	read := func(info filecache.ItemInfo, r io.Reader) error {
-		img = parent.clone()
-		img.relTargetDirFile.file = relTarget.file
-		img.sourceFilename = info.Name
-		// Make sure it's always loaded by sourceFilename.
-		img.openReadSeekerCloser = nil
+		img = parent.clone(nil)
+		rp := img.getResourcePaths()
+		rp.relTargetDirFile.file = relTarget.file
+		img.setSourceFilename(info.Name)
 
 		w, err := img.openDestinationsForWriting()
 		if err != nil {
@@ -109,29 +110,20 @@
 		return err
 	}
 
-	// create creates the image and encodes it to w (cache) and to its destinations.
+	// create creates the image and encodes it to the cache (w).
 	create := func(info filecache.ItemInfo, w io.WriteCloser) (err error) {
+		defer w.Close()
+
 		var conv image.Image
 		img, conv, err = createImage()
 		if err != nil {
-			w.Close()
 			return
 		}
-		img.relTargetDirFile.file = relTarget.file
-		img.sourceFilename = info.Name
+		rp := img.getResourcePaths()
+		rp.relTargetDirFile.file = relTarget.file
+		img.setSourceFilename(info.Name)
 
-		destinations, err := img.openDestinationsForWriting()
-		if err != nil {
-			w.Close()
-			return err
-		}
-
-		if destinations != nil {
-			w = hugio.NewMultiWriteCloser(w, destinations)
-		}
-		defer w.Close()
-
-		return img.encodeTo(conf, conv, w)
+		return img.EncodeTo(conf, conv, w)
 	}
 
 	// Now look in the file cache.
@@ -147,20 +139,21 @@
 	}
 
 	// The file is now stored in this cache.
-	img.sourceFs = c.fileCache.Fs
+	img.setSourceFs(c.fileCache.Fs)
 
 	c.mu.Lock()
-	if img2, found := c.store[key]; found {
+	if cachedImage, found = c.store[key]; found {
 		c.mu.Unlock()
-		return img2, nil
+		return cachedImage, nil
 	}
-	c.store[key] = img
+
+	imgAdapter := newResourceAdapter(parent.getSpec(), true, img)
+	c.store[key] = imgAdapter
 	c.mu.Unlock()
 
-	return img, nil
-
+	return imgAdapter, nil
 }
 
 func newImageCache(fileCache *filecache.Cache, ps *helpers.PathSpec) *imageCache {
-	return &imageCache{fileCache: fileCache, pathSpec: ps, store: make(map[string]*Image)}
+	return &imageCache{fileCache: fileCache, pathSpec: ps, store: make(map[string]*resourceAdapter)}
 }
--- a/resources/image_test.go
+++ b/resources/image_test.go
@@ -18,91 +18,76 @@
 	"math/rand"
 	"path/filepath"
 	"strconv"
+	"sync"
 	"testing"
 
-	"github.com/gohugoio/hugo/htesting/hqt"
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/resources/resource"
 
-	"github.com/disintegration/imaging"
+	"github.com/google/go-cmp/cmp"
 
-	"sync"
+	"github.com/gohugoio/hugo/htesting/hqt"
 
 	qt "github.com/frankban/quicktest"
 )
 
-func TestParseImageConfig(t *testing.T) {
-	for i, this := range []struct {
-		in     string
-		expect interface{}
-	}{
-		{"300x400", newImageConfig(300, 400, 0, 0, "", "")},
-		{"100x200 bottomRight", newImageConfig(100, 200, 0, 0, "", "BottomRight")},
-		{"10x20 topleft Lanczos", newImageConfig(10, 20, 0, 0, "Lanczos", "topleft")},
-		{"linear left 10x r180", newImageConfig(10, 0, 0, 180, "linear", "left")},
-		{"x20 riGht Cosine q95", newImageConfig(0, 20, 95, 0, "cosine", "right")},
+var eq = qt.CmpEquals(
+	cmp.Comparer(func(p1, p2 *resourceAdapter) bool {
+		return p1.resourceAdapterInner == p2.resourceAdapterInner
+	}),
+	cmp.Comparer(func(p1, p2 *genericResource) bool { return p1 == p2 }),
+	cmp.Comparer(func(m1, m2 media.Type) bool {
+		return m1.Type() == m2.Type()
+	}),
+)
 
-		{"", false},
-		{"foo", false},
-	} {
-		result, err := parseImageConfig(this.in)
-		if b, ok := this.expect.(bool); ok && !b {
-			if err == nil {
-				t.Errorf("[%d] parseImageConfig didn't return an expected error", i)
-			}
-		} else {
-			if err != nil {
-				t.Fatalf("[%d] err: %s", i, err)
-			}
-			if fmt.Sprint(result) != fmt.Sprint(this.expect) {
-				t.Fatalf("[%d] got\n%v\n but expected\n%v", i, result, this.expect)
-			}
-		}
-	}
-}
-
 func TestImageTransformBasic(t *testing.T) {
-
 	c := qt.New(t)
 
 	image := fetchSunset(c)
-	fileCache := image.spec.FileCaches.ImageCache().Fs
 
+	fileCache := image.(specProvider).getSpec().FileCaches.ImageCache().Fs
+
+	assertWidthHeight := func(img resource.Image, w, h int) {
+		c.Helper()
+		c.Assert(img, qt.Not(qt.IsNil))
+		c.Assert(img.Width(), qt.Equals, w)
+		c.Assert(img.Height(), qt.Equals, h)
+	}
+
 	c.Assert(image.RelPermalink(), qt.Equals, "/a/sunset.jpg")
 	c.Assert(image.ResourceType(), qt.Equals, "image")
+	assertWidthHeight(image, 900, 562)
 
 	resized, err := image.Resize("300x200")
 	c.Assert(err, qt.IsNil)
 	c.Assert(image != resized, qt.Equals, true)
-	c.Assert(image.genericResource != resized.genericResource, qt.Equals, true)
-	c.Assert(image.sourceFilename != resized.sourceFilename, qt.Equals, true)
+	c.Assert(image, qt.Not(eq), resized)
+	assertWidthHeight(resized, 300, 200)
+	assertWidthHeight(image, 900, 562)
 
 	resized0x, err := image.Resize("x200")
 	c.Assert(err, qt.IsNil)
-	c.Assert(resized0x.Width(), qt.Equals, 320)
-	c.Assert(resized0x.Height(), qt.Equals, 200)
-
+	assertWidthHeight(resized0x, 320, 200)
 	assertFileCache(c, fileCache, resized0x.RelPermalink(), 320, 200)
 
 	resizedx0, err := image.Resize("200x")
 	c.Assert(err, qt.IsNil)
-	c.Assert(resizedx0.Width(), qt.Equals, 200)
-	c.Assert(resizedx0.Height(), qt.Equals, 125)
+	assertWidthHeight(resizedx0, 200, 125)
 	assertFileCache(c, fileCache, resizedx0.RelPermalink(), 200, 125)
 
 	resizedAndRotated, err := image.Resize("x200 r90")
 	c.Assert(err, qt.IsNil)
-	c.Assert(resizedAndRotated.Width(), qt.Equals, 125)
-	c.Assert(resizedAndRotated.Height(), qt.Equals, 200)
+	assertWidthHeight(resizedAndRotated, 125, 200)
 	assertFileCache(c, fileCache, resizedAndRotated.RelPermalink(), 125, 200)
 
+	assertWidthHeight(resized, 300, 200)
 	c.Assert(resized.RelPermalink(), qt.Equals, "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_300x200_resize_q68_linear.jpg")
-	c.Assert(resized.Width(), qt.Equals, 300)
-	c.Assert(resized.Height(), qt.Equals, 200)
 
 	fitted, err := resized.Fit("50x50")
 	c.Assert(err, qt.IsNil)
 	c.Assert(fitted.RelPermalink(), qt.Equals, "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_625708021e2bb281c9f1002f88e4753f.jpg")
-	c.Assert(fitted.Width(), qt.Equals, 50)
-	c.Assert(fitted.Height(), qt.Equals, 33)
+	assertWidthHeight(fitted, 50, 33)
 
 	// Check the MD5 key threshold
 	fittedAgain, _ := fitted.Fit("10x20")
@@ -109,30 +94,25 @@
 	fittedAgain, err = fittedAgain.Fit("10x20")
 	c.Assert(err, qt.IsNil)
 	c.Assert(fittedAgain.RelPermalink(), qt.Equals, "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_3f65ba24dc2b7fba0f56d7f104519157.jpg")
-	c.Assert(fittedAgain.Width(), qt.Equals, 10)
-	c.Assert(fittedAgain.Height(), qt.Equals, 6)
+	assertWidthHeight(fittedAgain, 10, 6)
 
 	filled, err := image.Fill("200x100 bottomLeft")
 	c.Assert(err, qt.IsNil)
 	c.Assert(filled.RelPermalink(), qt.Equals, "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_200x100_fill_q68_linear_bottomleft.jpg")
-	c.Assert(filled.Width(), qt.Equals, 200)
-	c.Assert(filled.Height(), qt.Equals, 100)
+	assertWidthHeight(filled, 200, 100)
 	assertFileCache(c, fileCache, filled.RelPermalink(), 200, 100)
 
 	smart, err := image.Fill("200x100 smart")
 	c.Assert(err, qt.IsNil)
-	c.Assert(smart.RelPermalink(), qt.Equals, fmt.Sprintf("/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_200x100_fill_q68_linear_smart%d.jpg", smartCropVersionNumber))
-	c.Assert(smart.Width(), qt.Equals, 200)
-	c.Assert(smart.Height(), qt.Equals, 100)
+	c.Assert(smart.RelPermalink(), qt.Equals, fmt.Sprintf("/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_200x100_fill_q68_linear_smart%d.jpg", 1))
+	assertWidthHeight(smart, 200, 100)
 	assertFileCache(c, fileCache, smart.RelPermalink(), 200, 100)
 
 	// Check cache
 	filledAgain, err := image.Fill("200x100 bottomLeft")
 	c.Assert(err, qt.IsNil)
-	c.Assert(filled == filledAgain, qt.Equals, true)
-	c.Assert(filled.sourceFilename == filledAgain.sourceFilename, qt.Equals, true)
+	c.Assert(filled, eq, filledAgain)
 	assertFileCache(c, fileCache, filledAgain.RelPermalink(), 200, 100)
-
 }
 
 // https://github.com/gohugoio/hugo/issues/4261
@@ -158,6 +138,7 @@
 func TestImageTransformUppercaseExt(t *testing.T) {
 	c := qt.New(t)
 	image := fetchImage(c, "sunrise.JPG")
+
 	resized, err := image.Resize("200x")
 	c.Assert(err, qt.IsNil)
 	c.Assert(resized, qt.Not(qt.IsNil))
@@ -173,17 +154,16 @@
 		}
 
 		t.Run(name, func(t *testing.T) {
-
 			c := qt.New(t)
 			spec := newTestResourceOsFs(c)
 
-			check1 := func(img *Image) {
+			check1 := func(img resource.Image) {
 				resizedLink := "/a/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_100x50_resize_q75_box.jpg"
 				c.Assert(img.RelPermalink(), qt.Equals, resizedLink)
 				assertImageFile(c, spec.PublishFs, resizedLink, 100, 50)
 			}
 
-			check2 := func(img *Image) {
+			check2 := func(img resource.Image) {
 				c.Assert(img.RelPermalink(), qt.Equals, "/a/sunset.jpg")
 				assertImageFile(c, spec.PublishFs, "a/sunset.jpg", 900, 562)
 			}
@@ -198,7 +178,7 @@
 			resized, err := orignal.Resize("100x50")
 			c.Assert(err, qt.IsNil)
 
-			check1(resized)
+			check1(resized.(resource.Image))
 
 			if !checkOriginalFirst {
 				check2(orignal)
@@ -205,11 +185,9 @@
 			}
 		})
 	}
-
 }
 
 func TestImageTransformConcurrent(t *testing.T) {
-
 	var wg sync.WaitGroup
 
 	c := qt.New(t)
@@ -239,12 +217,7 @@
 						t.Error(err)
 					}
 
-					_, err = r2.decodeSource()
-					if err != nil {
-						t.Error("Err decode:", err)
-					}
-
-					img = r1
+					img = r2
 				}
 			}
 		}(i + 20)
@@ -253,58 +226,12 @@
 	wg.Wait()
 }
 
-func TestDecodeImaging(t *testing.T) {
-	c := qt.New(t)
-	m := map[string]interface{}{
-		"quality":        42,
-		"resampleFilter": "NearestNeighbor",
-		"anchor":         "topLeft",
-	}
-
-	imaging, err := decodeImaging(m)
-
-	c.Assert(err, qt.IsNil)
-	c.Assert(imaging.Quality, qt.Equals, 42)
-	c.Assert(imaging.ResampleFilter, qt.Equals, "nearestneighbor")
-	c.Assert(imaging.Anchor, qt.Equals, "topleft")
-
-	m = map[string]interface{}{}
-
-	imaging, err = decodeImaging(m)
-	c.Assert(err, qt.IsNil)
-	c.Assert(imaging.Quality, qt.Equals, defaultJPEGQuality)
-	c.Assert(imaging.ResampleFilter, qt.Equals, "box")
-	c.Assert(imaging.Anchor, qt.Equals, "smart")
-
-	_, err = decodeImaging(map[string]interface{}{
-		"quality": 123,
-	})
-	c.Assert(err, qt.Not(qt.IsNil))
-
-	_, err = decodeImaging(map[string]interface{}{
-		"resampleFilter": "asdf",
-	})
-	c.Assert(err, qt.Not(qt.IsNil))
-
-	_, err = decodeImaging(map[string]interface{}{
-		"anchor": "asdf",
-	})
-	c.Assert(err, qt.Not(qt.IsNil))
-
-	imaging, err = decodeImaging(map[string]interface{}{
-		"anchor": "Smart",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(imaging.Anchor, qt.Equals, "smart")
-
-}
-
 func TestImageWithMetadata(t *testing.T) {
 	c := qt.New(t)
 
 	image := fetchSunset(c)
 
-	var meta = []map[string]interface{}{
+	meta := []map[string]interface{}{
 		{
 			"title": "My Sunset",
 			"name":  "Sunset #:counter",
@@ -318,51 +245,50 @@
 	resized, err := image.Resize("200x")
 	c.Assert(err, qt.IsNil)
 	c.Assert(resized.Name(), qt.Equals, "Sunset #1")
-
 }
 
 func TestImageResize8BitPNG(t *testing.T) {
-
 	c := qt.New(t)
 
 	image := fetchImage(c, "gohugoio.png")
 
-	c.Assert(image.format, qt.Equals, imaging.PNG)
+	c.Assert(image.MediaType().Type(), qt.Equals, "image/png")
 	c.Assert(image.RelPermalink(), qt.Equals, "/a/gohugoio.png")
 	c.Assert(image.ResourceType(), qt.Equals, "image")
 
 	resized, err := image.Resize("800x")
 	c.Assert(err, qt.IsNil)
-	c.Assert(resized.format, qt.Equals, imaging.PNG)
+	c.Assert(resized.MediaType().Type(), qt.Equals, "image/png")
 	c.Assert(resized.RelPermalink(), qt.Equals, "/a/gohugoio_hu0e1b9e4a4be4d6f86c7b37b9ccce3fbc_73886_800x0_resize_linear_2.png")
 	c.Assert(resized.Width(), qt.Equals, 800)
-
 }
 
 func TestImageResizeInSubPath(t *testing.T) {
-
 	c := qt.New(t)
 
 	image := fetchImage(c, "sub/gohugoio2.png")
-	fileCache := image.spec.FileCaches.ImageCache().Fs
+	fileCache := image.(specProvider).getSpec().FileCaches.ImageCache().Fs
 
-	c.Assert(image.format, qt.Equals, imaging.PNG)
+	c.Assert(image.MediaType(), eq, media.PNGType)
 	c.Assert(image.RelPermalink(), qt.Equals, "/a/sub/gohugoio2.png")
 	c.Assert(image.ResourceType(), qt.Equals, "image")
 
 	resized, err := image.Resize("101x101")
 	c.Assert(err, qt.IsNil)
-	c.Assert(resized.format, qt.Equals, imaging.PNG)
+	c.Assert(resized.MediaType().Type(), qt.Equals, "image/png")
 	c.Assert(resized.RelPermalink(), qt.Equals, "/a/sub/gohugoio2_hu0e1b9e4a4be4d6f86c7b37b9ccce3fbc_73886_101x101_resize_linear_2.png")
 	c.Assert(resized.Width(), qt.Equals, 101)
 
 	assertFileCache(c, fileCache, resized.RelPermalink(), 101, 101)
 	publishedImageFilename := filepath.Clean(resized.RelPermalink())
-	assertImageFile(c, image.spec.BaseFs.PublishFs, publishedImageFilename, 101, 101)
-	c.Assert(image.spec.BaseFs.PublishFs.Remove(publishedImageFilename), qt.IsNil)
 
+	spec := image.(specProvider).getSpec()
+
+	assertImageFile(c, spec.BaseFs.PublishFs, publishedImageFilename, 101, 101)
+	c.Assert(spec.BaseFs.PublishFs.Remove(publishedImageFilename), qt.IsNil)
+
 	// Cleare mem cache to simulate reading from the file cache.
-	resized.spec.imageCache.clear()
+	spec.imageCache.clear()
 
 	resizedAgain, err := image.Resize("101x101")
 	c.Assert(err, qt.IsNil)
@@ -369,13 +295,12 @@
 	c.Assert(resizedAgain.RelPermalink(), qt.Equals, "/a/sub/gohugoio2_hu0e1b9e4a4be4d6f86c7b37b9ccce3fbc_73886_101x101_resize_linear_2.png")
 	c.Assert(resizedAgain.Width(), qt.Equals, 101)
 	assertFileCache(c, fileCache, resizedAgain.RelPermalink(), 101, 101)
-	assertImageFile(c, image.spec.BaseFs.PublishFs, publishedImageFilename, 101, 101)
-
+	assertImageFile(c, image.(specProvider).getSpec().BaseFs.PublishFs, publishedImageFilename, 101, 101)
 }
 
 func TestSVGImage(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	svg := fetchResourceForSpec(spec, c, "circle.svg")
 	c.Assert(svg, qt.Not(qt.IsNil))
 }
@@ -382,7 +307,7 @@
 
 func TestSVGImageContent(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	svg := fetchResourceForSpec(spec, c, "circle.svg")
 	c.Assert(svg, qt.Not(qt.IsNil))
 
--- /dev/null
+++ b/resources/images/config.go
@@ -1,0 +1,276 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/disintegration/imaging"
+	"github.com/mitchellh/mapstructure"
+)
+
+const (
+	defaultJPEGQuality    = 75
+	defaultResampleFilter = "box"
+)
+
+var (
+	imageFormats = map[string]imaging.Format{
+		".jpg":  imaging.JPEG,
+		".jpeg": imaging.JPEG,
+		".png":  imaging.PNG,
+		".tif":  imaging.TIFF,
+		".tiff": imaging.TIFF,
+		".bmp":  imaging.BMP,
+		".gif":  imaging.GIF,
+	}
+
+	// Add or increment if changes to an image format's processing requires
+	// re-generation.
+	imageFormatsVersions = map[imaging.Format]int{
+		imaging.PNG: 2, // Floyd Steinberg dithering
+	}
+
+	// Increment to mark all processed images as stale. Only use when absolutely needed.
+	// See the finer grained smartCropVersionNumber and imageFormatsVersions.
+	mainImageVersionNumber = 0
+
+	// Increment to mark all traced SVGs as stale.
+	traceVersionNumber = 0
+)
+
+var anchorPositions = map[string]imaging.Anchor{
+	strings.ToLower("Center"):      imaging.Center,
+	strings.ToLower("TopLeft"):     imaging.TopLeft,
+	strings.ToLower("Top"):         imaging.Top,
+	strings.ToLower("TopRight"):    imaging.TopRight,
+	strings.ToLower("Left"):        imaging.Left,
+	strings.ToLower("Right"):       imaging.Right,
+	strings.ToLower("BottomLeft"):  imaging.BottomLeft,
+	strings.ToLower("Bottom"):      imaging.Bottom,
+	strings.ToLower("BottomRight"): imaging.BottomRight,
+}
+
+var imageFilters = map[string]imaging.ResampleFilter{
+	strings.ToLower("NearestNeighbor"):   imaging.NearestNeighbor,
+	strings.ToLower("Box"):               imaging.Box,
+	strings.ToLower("Linear"):            imaging.Linear,
+	strings.ToLower("Hermite"):           imaging.Hermite,
+	strings.ToLower("MitchellNetravali"): imaging.MitchellNetravali,
+	strings.ToLower("CatmullRom"):        imaging.CatmullRom,
+	strings.ToLower("BSpline"):           imaging.BSpline,
+	strings.ToLower("Gaussian"):          imaging.Gaussian,
+	strings.ToLower("Lanczos"):           imaging.Lanczos,
+	strings.ToLower("Hann"):              imaging.Hann,
+	strings.ToLower("Hamming"):           imaging.Hamming,
+	strings.ToLower("Blackman"):          imaging.Blackman,
+	strings.ToLower("Bartlett"):          imaging.Bartlett,
+	strings.ToLower("Welch"):             imaging.Welch,
+	strings.ToLower("Cosine"):            imaging.Cosine,
+}
+
+func ImageFormatFromExt(ext string) (imaging.Format, bool) {
+	f, found := imageFormats[ext]
+	return f, found
+}
+
+func DecodeConfig(m map[string]interface{}) (Imaging, error) {
+	var i Imaging
+	if err := mapstructure.WeakDecode(m, &i); err != nil {
+		return i, err
+	}
+
+	if i.Quality == 0 {
+		i.Quality = defaultJPEGQuality
+	} else if i.Quality < 0 || i.Quality > 100 {
+		return i, errors.New("JPEG quality must be a number between 1 and 100")
+	}
+
+	if i.Anchor == "" || strings.EqualFold(i.Anchor, SmartCropIdentifier) {
+		i.Anchor = SmartCropIdentifier
+	} else {
+		i.Anchor = strings.ToLower(i.Anchor)
+		if _, found := anchorPositions[i.Anchor]; !found {
+			return i, errors.New("invalid anchor value in imaging config")
+		}
+	}
+
+	if i.ResampleFilter == "" {
+		i.ResampleFilter = defaultResampleFilter
+	} else {
+		filter := strings.ToLower(i.ResampleFilter)
+		_, found := imageFilters[filter]
+		if !found {
+			return i, fmt.Errorf("%q is not a valid resample filter", filter)
+		}
+		i.ResampleFilter = filter
+	}
+
+	return i, nil
+}
+
+func DecodeImageConfig(action, config string, defaults Imaging) (ImageConfig, error) {
+	var (
+		c   ImageConfig
+		err error
+	)
+
+	c.Action = action
+
+	if config == "" {
+		return c, errors.New("image config cannot be empty")
+	}
+
+	parts := strings.Fields(config)
+	for _, part := range parts {
+		part = strings.ToLower(part)
+
+		if part == SmartCropIdentifier {
+			c.AnchorStr = SmartCropIdentifier
+		} else if pos, ok := anchorPositions[part]; ok {
+			c.Anchor = pos
+			c.AnchorStr = part
+		} else if filter, ok := imageFilters[part]; ok {
+			c.Filter = filter
+			c.FilterStr = part
+		} else if part[0] == 'q' {
+			c.Quality, err = strconv.Atoi(part[1:])
+			if err != nil {
+				return c, err
+			}
+			if c.Quality < 1 || c.Quality > 100 {
+				return c, errors.New("quality ranges from 1 to 100 inclusive")
+			}
+		} else if part[0] == 'r' {
+			c.Rotate, err = strconv.Atoi(part[1:])
+			if err != nil {
+				return c, err
+			}
+		} else if strings.Contains(part, "x") {
+			widthHeight := strings.Split(part, "x")
+			if len(widthHeight) <= 2 {
+				first := widthHeight[0]
+				if first != "" {
+					c.Width, err = strconv.Atoi(first)
+					if err != nil {
+						return c, err
+					}
+				}
+
+				if len(widthHeight) == 2 {
+					second := widthHeight[1]
+					if second != "" {
+						c.Height, err = strconv.Atoi(second)
+						if err != nil {
+							return c, err
+						}
+					}
+				}
+			} else {
+				return c, errors.New("invalid image dimensions")
+			}
+
+		}
+	}
+
+	if c.Width == 0 && c.Height == 0 {
+		return c, errors.New("must provide Width or Height")
+	}
+
+	if c.FilterStr == "" {
+		c.FilterStr = defaults.ResampleFilter
+		c.Filter = imageFilters[c.FilterStr]
+	}
+
+	if c.AnchorStr == "" {
+		c.AnchorStr = defaults.Anchor
+		if !strings.EqualFold(c.AnchorStr, SmartCropIdentifier) {
+			c.Anchor = anchorPositions[c.AnchorStr]
+		}
+	}
+
+	return c, nil
+}
+
+// ImageConfig holds configuration to create a new image from an existing one, resize etc.
+type ImageConfig struct {
+	Action string
+
+	// Quality ranges from 1 to 100 inclusive, higher is better.
+	// This is only relevant for JPEG images.
+	// Default is 75.
+	Quality int
+
+	// Rotate rotates an image by the given angle counter-clockwise.
+	// The rotation will be performed first.
+	Rotate int
+
+	Width  int
+	Height int
+
+	Filter    imaging.ResampleFilter
+	FilterStr string
+
+	Anchor    imaging.Anchor
+	AnchorStr string
+}
+
+func (i ImageConfig) Key(format imaging.Format) string {
+	k := strconv.Itoa(i.Width) + "x" + strconv.Itoa(i.Height)
+	if i.Action != "" {
+		k += "_" + i.Action
+	}
+	if i.Quality > 0 {
+		k += "_q" + strconv.Itoa(i.Quality)
+	}
+	if i.Rotate != 0 {
+		k += "_r" + strconv.Itoa(i.Rotate)
+	}
+	anchor := i.AnchorStr
+	if anchor == SmartCropIdentifier {
+		anchor = anchor + strconv.Itoa(smartCropVersionNumber)
+	}
+
+	k += "_" + i.FilterStr
+
+	if strings.EqualFold(i.Action, "fill") {
+		k += "_" + anchor
+	}
+
+	if v, ok := imageFormatsVersions[format]; ok {
+		k += "_" + strconv.Itoa(v)
+	}
+
+	if mainImageVersionNumber > 0 {
+		k += "_" + strconv.Itoa(mainImageVersionNumber)
+	}
+
+	return k
+}
+
+// Imaging contains default image processing configuration. This will be fetched
+// from site (or language) config.
+type Imaging struct {
+	// Default image quality setting (1-100). Only used for JPEG images.
+	Quality int
+
+	// Resample filter used. See https://github.com/disintegration/imaging
+	ResampleFilter string
+
+	// The anchor used in Fill. Default is "smart", i.e. Smart Crop.
+	Anchor string
+}
--- /dev/null
+++ b/resources/images/config_test.go
@@ -1,0 +1,125 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestDecodeConfig(t *testing.T) {
+	c := qt.New(t)
+	m := map[string]interface{}{
+		"quality":        42,
+		"resampleFilter": "NearestNeighbor",
+		"anchor":         "topLeft",
+	}
+
+	imaging, err := DecodeConfig(m)
+
+	c.Assert(err, qt.IsNil)
+	c.Assert(imaging.Quality, qt.Equals, 42)
+	c.Assert(imaging.ResampleFilter, qt.Equals, "nearestneighbor")
+	c.Assert(imaging.Anchor, qt.Equals, "topleft")
+
+	m = map[string]interface{}{}
+
+	imaging, err = DecodeConfig(m)
+	c.Assert(err, qt.IsNil)
+	c.Assert(imaging.Quality, qt.Equals, defaultJPEGQuality)
+	c.Assert(imaging.ResampleFilter, qt.Equals, "box")
+	c.Assert(imaging.Anchor, qt.Equals, "smart")
+
+	_, err = DecodeConfig(map[string]interface{}{
+		"quality": 123,
+	})
+	c.Assert(err, qt.Not(qt.IsNil))
+
+	_, err = DecodeConfig(map[string]interface{}{
+		"resampleFilter": "asdf",
+	})
+	c.Assert(err, qt.Not(qt.IsNil))
+
+	_, err = DecodeConfig(map[string]interface{}{
+		"anchor": "asdf",
+	})
+	c.Assert(err, qt.Not(qt.IsNil))
+
+	imaging, err = DecodeConfig(map[string]interface{}{
+		"anchor": "Smart",
+	})
+	c.Assert(err, qt.IsNil)
+	c.Assert(imaging.Anchor, qt.Equals, "smart")
+}
+
+func TestDecodeImageConfig(t *testing.T) {
+	for i, this := range []struct {
+		in     string
+		expect interface{}
+	}{
+		{"300x400", newImageConfig(300, 400, 0, 0, "", "")},
+		{"100x200 bottomRight", newImageConfig(100, 200, 0, 0, "", "BottomRight")},
+		{"10x20 topleft Lanczos", newImageConfig(10, 20, 0, 0, "Lanczos", "topleft")},
+		{"linear left 10x r180", newImageConfig(10, 0, 0, 180, "linear", "left")},
+		{"x20 riGht Cosine q95", newImageConfig(0, 20, 95, 0, "cosine", "right")},
+
+		{"", false},
+		{"foo", false},
+	} {
+
+		result, err := DecodeImageConfig("resize", this.in, Imaging{})
+		if b, ok := this.expect.(bool); ok && !b {
+			if err == nil {
+				t.Errorf("[%d] parseImageConfig didn't return an expected error", i)
+			}
+		} else {
+			if err != nil {
+				t.Fatalf("[%d] err: %s", i, err)
+			}
+			if fmt.Sprint(result) != fmt.Sprint(this.expect) {
+				t.Fatalf("[%d] got\n%v\n but expected\n%v", i, result, this.expect)
+			}
+		}
+	}
+}
+
+func newImageConfig(width, height, quality, rotate int, filter, anchor string) ImageConfig {
+	var c ImageConfig
+	c.Action = "resize"
+	c.Width = width
+	c.Height = height
+	c.Quality = quality
+	c.Rotate = rotate
+
+	if filter != "" {
+		filter = strings.ToLower(filter)
+		if v, ok := imageFilters[filter]; ok {
+			c.Filter = v
+			c.FilterStr = filter
+		}
+	}
+
+	if anchor != "" {
+		anchor = strings.ToLower(anchor)
+		if v, ok := anchorPositions[anchor]; ok {
+			c.Anchor = v
+			c.AnchorStr = anchor
+		}
+	}
+
+	return c
+}
--- /dev/null
+++ b/resources/images/image.go
@@ -1,0 +1,170 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"image"
+	"image/jpeg"
+	"io"
+	"sync"
+
+	"github.com/disintegration/imaging"
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/pkg/errors"
+)
+
+func NewImage(f imaging.Format, proc *ImageProcessor, img image.Image, s Spec) *Image {
+	if img != nil {
+		return &Image{
+			Format: f,
+			Proc:   proc,
+			Spec:   s,
+			imageConfig: &imageConfig{
+				config:       imageConfigFromImage(img),
+				configLoaded: true,
+			},
+		}
+	}
+	return &Image{Format: f, Proc: proc, Spec: s, imageConfig: &imageConfig{}}
+}
+
+type Image struct {
+	Format imaging.Format
+
+	Proc *ImageProcessor
+
+	Spec Spec
+
+	*imageConfig
+}
+
+func (i *Image) EncodeTo(conf ImageConfig, img image.Image, w io.Writer) error {
+	switch i.Format {
+	case imaging.JPEG:
+
+		var rgba *image.RGBA
+		quality := conf.Quality
+
+		if nrgba, ok := img.(*image.NRGBA); ok {
+			if nrgba.Opaque() {
+				rgba = &image.RGBA{
+					Pix:    nrgba.Pix,
+					Stride: nrgba.Stride,
+					Rect:   nrgba.Rect,
+				}
+			}
+		}
+		if rgba != nil {
+			return jpeg.Encode(w, rgba, &jpeg.Options{Quality: quality})
+		}
+		return jpeg.Encode(w, img, &jpeg.Options{Quality: quality})
+	default:
+		return imaging.Encode(w, img, i.Format)
+	}
+}
+
+// Height returns i's height.
+func (i *Image) Height() int {
+	i.initConfig()
+	return i.config.Height
+}
+
+// Width returns i's width.
+func (i *Image) Width() int {
+	i.initConfig()
+	return i.config.Width
+}
+
+func (i Image) WithImage(img image.Image) *Image {
+	i.Spec = nil
+	i.imageConfig = &imageConfig{
+		config:       imageConfigFromImage(img),
+		configLoaded: true,
+	}
+
+	return &i
+}
+
+func (i Image) WithSpec(s Spec) *Image {
+	i.Spec = s
+	i.imageConfig = &imageConfig{}
+	return &i
+}
+
+func (i *Image) initConfig() error {
+	var err error
+	i.configInit.Do(func() {
+		if i.configLoaded {
+			return
+		}
+
+		var (
+			f      hugio.ReadSeekCloser
+			config image.Config
+		)
+
+		f, err = i.Spec.ReadSeekCloser()
+		if err != nil {
+			return
+		}
+		defer f.Close()
+
+		config, _, err = image.DecodeConfig(f)
+		if err != nil {
+			return
+		}
+		i.config = config
+	})
+
+	if err != nil {
+		return errors.Wrap(err, "failed to load image config")
+	}
+
+	return nil
+}
+
+type ImageProcessor struct {
+	Cfg Imaging
+}
+
+func (p *ImageProcessor) Fill(src image.Image, conf ImageConfig) (image.Image, error) {
+	if conf.AnchorStr == SmartCropIdentifier {
+		return smartCrop(src, conf.Width, conf.Height, conf.Anchor, conf.Filter)
+	}
+	return imaging.Fill(src, conf.Width, conf.Height, conf.Anchor, conf.Filter), nil
+}
+
+func (p *ImageProcessor) Fit(src image.Image, conf ImageConfig) (image.Image, error) {
+	return imaging.Fit(src, conf.Width, conf.Height, conf.Filter), nil
+}
+
+func (p *ImageProcessor) Resize(src image.Image, conf ImageConfig) (image.Image, error) {
+	return imaging.Resize(src, conf.Width, conf.Height, conf.Filter), nil
+}
+
+type Spec interface {
+	// Loads the image source.
+	ReadSeekCloser() (hugio.ReadSeekCloser, error)
+}
+
+type imageConfig struct {
+	config       image.Config
+	configInit   sync.Once
+	configLoaded bool
+}
+
+func imageConfigFromImage(img image.Image) image.Config {
+	b := img.Bounds()
+	return image.Config{Width: b.Max.X, Height: b.Max.Y}
+}
--- /dev/null
+++ b/resources/images/smartcrop.go
@@ -1,0 +1,75 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"image"
+
+	"github.com/disintegration/imaging"
+	"github.com/muesli/smartcrop"
+)
+
+const (
+	// Do not change.
+	// TODO(bep) image unexport
+	SmartCropIdentifier = "smart"
+
+	// This is just a increment, starting on 1. If Smart Crop improves its cropping, we
+	// need a way to trigger a re-generation of the crops in the wild, so increment this.
+	smartCropVersionNumber = 1
+)
+
+func newSmartCropAnalyzer(filter imaging.ResampleFilter) smartcrop.Analyzer {
+	return smartcrop.NewAnalyzer(imagingResizer{filter: filter})
+}
+
+// Needed by smartcrop
+type imagingResizer struct {
+	filter imaging.ResampleFilter
+}
+
+func (r imagingResizer) Resize(img image.Image, width, height uint) image.Image {
+	return imaging.Resize(img, int(width), int(height), r.filter)
+}
+
+func smartCrop(img image.Image, width, height int, anchor imaging.Anchor, filter imaging.ResampleFilter) (*image.NRGBA, error) {
+	if width <= 0 || height <= 0 {
+		return &image.NRGBA{}, nil
+	}
+
+	srcBounds := img.Bounds()
+	srcW := srcBounds.Dx()
+	srcH := srcBounds.Dy()
+
+	if srcW <= 0 || srcH <= 0 {
+		return &image.NRGBA{}, nil
+	}
+
+	if srcW == width && srcH == height {
+		return imaging.Clone(img), nil
+	}
+
+	smart := newSmartCropAnalyzer(filter)
+
+	rect, err := smart.FindBestCrop(img, width, height)
+	if err != nil {
+		return nil, err
+	}
+
+	b := img.Bounds().Intersect(rect)
+
+	cropped := imaging.Crop(img, b)
+
+	return imaging.Resize(cropped, width, height, filter), nil
+}
--- /dev/null
+++ b/resources/internal/key.go
@@ -1,0 +1,61 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"strconv"
+
+	bp "github.com/gohugoio/hugo/bufferpool"
+
+	"github.com/mitchellh/hashstructure"
+)
+
+// ResourceTransformationKey are provided by the different transformation implementations.
+// It identifies the transformation (name) and its configuration (elements).
+// We combine this in a chain with the rest of the transformations
+// with the target filename and a content hash of the origin to use as cache key.
+type ResourceTransformationKey struct {
+	Name     string
+	elements []interface{}
+}
+
+// NewResourceTransformationKey creates a new ResourceTransformationKey from the transformation
+// name and elements. We will create a 64 bit FNV hash from the elements, which when combined
+// with the other key elements should be unique for all practical applications.
+func NewResourceTransformationKey(name string, elements ...interface{}) ResourceTransformationKey {
+	return ResourceTransformationKey{Name: name, elements: elements}
+}
+
+// Value returns the Key as a string.
+// Do not change this without good reasons.
+func (k ResourceTransformationKey) Value() string {
+	if len(k.elements) == 0 {
+		return k.Name
+	}
+
+	sb := bp.GetBuffer()
+	defer bp.PutBuffer(sb)
+
+	sb.WriteString(k.Name)
+	for _, element := range k.elements {
+		hash, err := hashstructure.Hash(element, nil)
+		if err != nil {
+			panic(err)
+		}
+		sb.WriteString("_")
+		sb.WriteString(strconv.FormatUint(hash, 10))
+	}
+
+	return sb.String()
+}
--- /dev/null
+++ b/resources/internal/key_test.go
@@ -1,0 +1,36 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+type testStruct struct {
+	Name string
+	V1   int64
+	V2   int32
+	V3   int
+	V4   uint64
+}
+
+func TestResourceTransformationKey(t *testing.T) {
+	// We really need this key to be portable across OSes.
+	key := NewResourceTransformationKey("testing",
+		testStruct{Name: "test", V1: int64(10), V2: int32(20), V3: 30, V4: uint64(40)})
+	c := qt.New(t)
+	c.Assert("testing_518996646957295636", qt.Equals, key.Value())
+}
--- a/resources/resource.go
+++ b/resources/resource.go
@@ -17,23 +17,17 @@
 	"fmt"
 	"io"
 	"io/ioutil"
-	"mime"
 	"os"
 	"path"
 	"path/filepath"
-	"strings"
 	"sync"
 
 	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/source"
 
-	"github.com/gohugoio/hugo/output"
-	"github.com/gohugoio/hugo/tpl"
 	"github.com/pkg/errors"
 
-	"github.com/gohugoio/hugo/cache/filecache"
-	"github.com/gohugoio/hugo/common/collections"
 	"github.com/gohugoio/hugo/common/hugio"
-	"github.com/gohugoio/hugo/common/loggers"
 	"github.com/gohugoio/hugo/resources/page"
 	"github.com/gohugoio/hugo/resources/resource"
 
@@ -40,7 +34,6 @@
 	"github.com/spf13/afero"
 
 	"github.com/gohugoio/hugo/helpers"
-	"github.com/gohugoio/hugo/source"
 )
 
 var (
@@ -51,80 +44,10 @@
 	_ resource.Cloner                  = (*genericResource)(nil)
 	_ resource.ResourcesLanguageMerger = (*resource.Resources)(nil)
 	_ permalinker                      = (*genericResource)(nil)
-	_ collections.Slicer               = (*genericResource)(nil)
 	_ resource.Identifier              = (*genericResource)(nil)
+	_ fileInfo                         = (*genericResource)(nil)
 )
 
-var noData = make(map[string]interface{})
-
-type permalinker interface {
-	relPermalinkFor(target string) string
-	permalinkFor(target string) string
-	relTargetPathsFor(target string) []string
-	relTargetPaths() []string
-	TargetPath() string
-}
-
-type Spec struct {
-	*helpers.PathSpec
-
-	MediaTypes    media.Types
-	OutputFormats output.Formats
-
-	Logger *loggers.Logger
-
-	TextTemplates tpl.TemplateParseFinder
-
-	Permalinks page.PermalinkExpander
-
-	// Holds default filter settings etc.
-	imaging *Imaging
-
-	imageCache    *imageCache
-	ResourceCache *ResourceCache
-	FileCaches    filecache.Caches
-}
-
-func NewSpec(
-	s *helpers.PathSpec,
-	fileCaches filecache.Caches,
-	logger *loggers.Logger,
-	outputFormats output.Formats,
-	mimeTypes media.Types) (*Spec, error) {
-
-	imaging, err := decodeImaging(s.Cfg.GetStringMap("imaging"))
-	if err != nil {
-		return nil, err
-	}
-
-	if logger == nil {
-		logger = loggers.NewErrorLogger()
-	}
-
-	permalinks, err := page.NewPermalinkExpander(s)
-	if err != nil {
-		return nil, err
-	}
-
-	rs := &Spec{PathSpec: s,
-		Logger:        logger,
-		imaging:       &imaging,
-		MediaTypes:    mimeTypes,
-		OutputFormats: outputFormats,
-		Permalinks:    permalinks,
-		FileCaches:    fileCaches,
-		imageCache: newImageCache(
-			fileCaches.ImageCache(),
-
-			s,
-		)}
-
-	rs.ResourceCache = newResourceCache(rs)
-
-	return rs, nil
-
-}
-
 type ResourceSourceDescriptor struct {
 	// TargetPaths is a callback to fetch paths's relative to its owner.
 	TargetPaths func() page.TargetPaths
@@ -161,136 +84,77 @@
 	return r.SourceFilename
 }
 
-func (r *Spec) New(fd ResourceSourceDescriptor) (resource.Resource, error) {
-	return r.newResourceFor(fd)
+type ResourceTransformer interface {
+	resource.Resource
+	Transformer
 }
 
-func (r *Spec) newResourceFor(fd ResourceSourceDescriptor) (resource.Resource, error) {
-	if fd.OpenReadSeekCloser == nil {
-		if fd.SourceFile != nil && fd.SourceFilename != "" {
-			return nil, errors.New("both SourceFile and AbsSourceFilename provided")
-		} else if fd.SourceFile == nil && fd.SourceFilename == "" {
-			return nil, errors.New("either SourceFile or AbsSourceFilename must be provided")
-		}
-	}
+type Transformer interface {
+	Transform(...ResourceTransformation) (ResourceTransformer, error)
+}
 
-	if fd.RelTargetFilename == "" {
-		fd.RelTargetFilename = fd.Filename()
-	}
-
-	if len(fd.TargetBasePaths) == 0 {
-		// If not set, we publish the same resource to all hosts.
-		fd.TargetBasePaths = r.MultihostTargetBasePaths
-	}
-
-	return r.newResource(fd.Fs, fd)
+type baseResourceResource interface {
+	resource.Cloner
+	resource.ContentProvider
+	resource.Resource
+	resource.Identifier
 }
 
-func (r *Spec) newResource(sourceFs afero.Fs, fd ResourceSourceDescriptor) (resource.Resource, error) {
-	fi := fd.FileInfo
-	var sourceFilename string
+type baseResourceInternal interface {
+	resource.Source
 
-	if fd.OpenReadSeekCloser != nil {
-	} else if fd.SourceFilename != "" {
-		var err error
-		fi, err = sourceFs.Stat(fd.SourceFilename)
-		if err != nil {
-			if os.IsNotExist(err) {
-				return nil, nil
-			}
-			return nil, err
-		}
-		sourceFilename = fd.SourceFilename
-	} else {
-		sourceFilename = fd.SourceFile.Filename()
-	}
+	fileInfo
+	metaAssigner
+	targetPather
 
-	if fd.RelTargetFilename == "" {
-		fd.RelTargetFilename = sourceFilename
-	}
+	ReadSeekCloser() (hugio.ReadSeekCloser, error)
 
-	ext := strings.ToLower(filepath.Ext(fd.RelTargetFilename))
-	mimeType, found := r.MediaTypes.GetFirstBySuffix(strings.TrimPrefix(ext, "."))
-	// TODO(bep) we need to handle these ambigous types better, but in this context
-	// we most likely want the application/xml type.
-	if mimeType.Suffix() == "xml" && mimeType.SubType == "rss" {
-		mimeType, found = r.MediaTypes.GetByType("application/xml")
-	}
+	// Internal
+	cloneWithUpdates(*transformationUpdate) (baseResource, error)
+	tryTransformedFileCache(key string, u *transformationUpdate) io.ReadCloser
 
-	if !found {
-		// A fallback. Note that mime.TypeByExtension is slow by Hugo standards,
-		// so we should configure media types to avoid this lookup for most
-		// situations.
-		mimeStr := mime.TypeByExtension(ext)
-		if mimeStr != "" {
-			mimeType, _ = media.FromStringAndExt(mimeStr, ext)
-		}
-	}
+	specProvider
+	getResourcePaths() *resourcePathDescriptor
+	getTargetFilenames() []string
+	openDestinationsForWriting() (io.WriteCloser, error)
+	openPublishFileForWriting(relTargetPath string) (io.WriteCloser, error)
 
-	gr := r.newGenericResourceWithBase(
-		sourceFs,
-		fd.LazyPublish,
-		fd.OpenReadSeekCloser,
-		fd.TargetBasePaths,
-		fd.TargetPaths,
-		fi,
-		sourceFilename,
-		fd.RelTargetFilename,
-		mimeType)
-
-	if mimeType.MainType == "image" {
-		imgFormat, ok := imageFormats[ext]
-		if !ok {
-			// This allows SVG etc. to be used as resources. They will not have the methods of the Image, but
-			// that would not (currently) have worked.
-			return gr, nil
-		}
-
-		if err := gr.initHash(); err != nil {
-			return nil, err
-		}
-
-		return &Image{
-			format:          imgFormat,
-			imaging:         r.imaging,
-			genericResource: gr}, nil
-	}
-	return gr, nil
-
+	relTargetPathForRel(rel string, addBaseTargetPath, isAbs, isURL bool) string
 }
 
-// TODO(bep) unify
-func (r *Spec) IsInImageCache(key string) bool {
-	// This is used for cache pruning. We currently only have images, but we could
-	// imagine expanding on this.
-	return r.imageCache.isInCache(key)
+type specProvider interface {
+	getSpec() *Spec
 }
 
-func (r *Spec) DeleteCacheByPrefix(prefix string) {
-	r.imageCache.deleteByPrefix(prefix)
+type baseResource interface {
+	baseResourceResource
+	baseResourceInternal
 }
 
-func (r *Spec) ClearCaches() {
-	r.imageCache.clear()
-	r.ResourceCache.clear()
+type commonResource struct {
 }
 
-func (r *Spec) CacheStats() string {
-	r.imageCache.mu.RLock()
-	defer r.imageCache.mu.RUnlock()
-
-	s := fmt.Sprintf("Cache entries: %d", len(r.imageCache.store))
-
-	count := 0
-	for k := range r.imageCache.store {
-		if count > 5 {
-			break
+// Slice is not meant to be used externally. It's a bridge function
+// for the template functions. See collections.Slice.
+func (commonResource) Slice(in interface{}) (interface{}, error) {
+	switch items := in.(type) {
+	case resource.Resources:
+		return items, nil
+	case []interface{}:
+		groups := make(resource.Resources, len(items))
+		for i, v := range items {
+			g, ok := v.(resource.Resource)
+			if !ok {
+				return nil, fmt.Errorf("type %T is not a Resource", v)
+			}
+			groups[i] = g
+			{
+			}
 		}
-		s += "\n" + k
-		count++
+		return groups, nil
+	default:
+		return nil, fmt.Errorf("invalid slice type %T", items)
 	}
-
-	return s
 }
 
 type dirFile struct {
@@ -304,93 +168,35 @@
 	return path.Join(d.dir, d.file)
 }
 
-type resourcePathDescriptor struct {
-	// The relative target directory and filename.
-	relTargetDirFile dirFile
-
-	// Callback used to construct a target path relative to its owner.
-	targetPathBuilder func() page.TargetPaths
-
-	// This will normally be the same as above, but this will only apply to publishing
-	// of resources. It may be mulltiple values when in multihost mode.
-	baseTargetPathDirs []string
-
-	// baseOffset is set when the output format's path has a offset, e.g. for AMP.
-	baseOffset string
+type fileInfo interface {
+	getSourceFilename() string
+	setSourceFilename(string)
+	setSourceFs(afero.Fs)
+	hash() (string, error)
+	size() int
 }
 
-type resourceContent struct {
-	content     string
-	contentInit sync.Once
-}
-
-type resourceHash struct {
-	hash     string
-	hashInit sync.Once
-}
-
-type publishOnce struct {
-	publisherInit sync.Once
-	publisherErr  error
-	logger        *loggers.Logger
-}
-
-func (l *publishOnce) publish(s resource.Source) error {
-	l.publisherInit.Do(func() {
-		l.publisherErr = s.Publish()
-		if l.publisherErr != nil {
-			l.logger.ERROR.Printf("failed to publish Resource: %s", l.publisherErr)
-		}
-	})
-	return l.publisherErr
-}
-
 // genericResource represents a generic linkable resource.
 type genericResource struct {
-	commonResource
-	resourcePathDescriptor
+	*resourcePathDescriptor
+	*resourceFileInfo
+	*resourceContent
 
+	spec *Spec
+
 	title  string
 	name   string
 	params map[string]interface{}
+	data   map[string]interface{}
 
-	// Absolute filename to the source, including any content folder path.
-	// Note that this is absolute in relation to the filesystem it is stored in.
-	// It can be a base path filesystem, and then this filename will not match
-	// the path to the file on the real filesystem.
-	sourceFilename string
-
-	// Will be set if this resource is backed by something other than a file.
-	openReadSeekerCloser resource.OpenReadSeekCloser
-
-	// A hash of the source content. Is only calculated in caching situations.
-	*resourceHash
-
-	// This may be set to tell us to look in another filesystem for this resource.
-	// We, by default, use the sourceFs filesystem in the spec below.
-	sourceFs afero.Fs
-
-	spec *Spec
-
 	resourceType string
 	mediaType    media.Type
-
-	osFileInfo os.FileInfo
-
-	// We create copies of this struct, so this needs to be a pointer.
-	*resourceContent
-
-	// May be set to signal lazy/delayed publishing.
-	*publishOnce
 }
 
-type commonResource struct {
+func (l *genericResource) Clone() resource.Resource {
+	return l.clone()
 }
 
-func (l *genericResource) Data() interface{} {
-	return noData
-}
-
 func (l *genericResource) Content() (interface{}, error) {
 	if err := l.initContent(); err != nil {
 		return nil, err
@@ -399,72 +205,80 @@
 	return l.content, nil
 }
 
-func (l *genericResource) ReadSeekCloser() (hugio.ReadSeekCloser, error) {
-	if l.openReadSeekerCloser != nil {
-		return l.openReadSeekerCloser()
+func (l *genericResource) Data() interface{} {
+	return l.data
+}
+
+func (l *genericResource) Key() string {
+	return l.relTargetDirFile.path()
+}
+
+func (l *genericResource) MediaType() media.Type {
+	return l.mediaType
+}
+
+func (l *genericResource) Name() string {
+	return l.name
+}
+
+func (l *genericResource) Params() map[string]interface{} {
+	return l.params
+}
+
+func (l *genericResource) Permalink() string {
+	return l.spec.PermalinkForBaseURL(l.relPermalinkForRel(l.relTargetDirFile.path(), true), l.spec.BaseURL.HostURL())
+}
+
+func (l *genericResource) Publish() error {
+	fr, err := l.ReadSeekCloser()
+	if err != nil {
+		return err
 	}
+	defer fr.Close()
 
-	f, err := l.getSourceFs().Open(l.sourceFilename)
+	fw, err := helpers.OpenFilesForWriting(l.spec.BaseFs.PublishFs, l.getTargetFilenames()...)
 	if err != nil {
-		return nil, err
+		return err
 	}
-	return f, nil
+	defer fw.Close()
 
+	_, err = io.Copy(fw, fr)
+	return err
 }
 
-func (l *genericResource) MediaType() media.Type {
-	return l.mediaType
+func (l *genericResource) RelPermalink() string {
+	return l.relPermalinkFor(l.relTargetDirFile.path())
 }
 
-// Implement the Cloner interface.
-func (l genericResource) WithNewBase(base string) resource.Resource {
-	l.baseOffset = base
-	l.resourceContent = &resourceContent{}
-	return &l
+func (l *genericResource) ResourceType() string {
+	return l.resourceType
 }
 
-// Slice is not meant to be used externally. It's a bridge function
-// for the template functions. See collections.Slice.
-func (commonResource) Slice(in interface{}) (interface{}, error) {
-	switch items := in.(type) {
-	case resource.Resources:
-		return items, nil
-	case []interface{}:
-		groups := make(resource.Resources, len(items))
-		for i, v := range items {
-			g, ok := v.(resource.Resource)
-			if !ok {
-				return nil, fmt.Errorf("type %T is not a Resource", v)
-			}
-			groups[i] = g
-		}
-		return groups, nil
-	default:
-		return nil, fmt.Errorf("invalid slice type %T", items)
-	}
+func (l *genericResource) String() string {
+	return fmt.Sprintf("Resource(%s: %s)", l.resourceType, l.name)
 }
 
-func (l *genericResource) initHash() error {
-	var err error
-	l.hashInit.Do(func() {
-		var hash string
-		var f hugio.ReadSeekCloser
-		f, err = l.ReadSeekCloser()
-		if err != nil {
-			err = errors.Wrap(err, "failed to open source file")
-			return
-		}
-		defer f.Close()
+// Path is stored with Unix style slashes.
+func (l *genericResource) TargetPath() string {
+	return l.relTargetDirFile.path()
+}
 
-		hash, err = helpers.MD5FromFileFast(f)
-		if err != nil {
-			return
-		}
-		l.hash = hash
+func (l *genericResource) Title() string {
+	return l.title
+}
 
-	})
+func (l *genericResource) createBasePath(rel string, isURL bool) string {
+	if l.targetPathBuilder == nil {
+		return rel
+	}
+	tp := l.targetPathBuilder()
 
-	return err
+	if isURL {
+		return path.Join(tp.SubResourceBaseLink, rel)
+	}
+
+	// TODO(bep) path
+	return path.Join(filepath.ToSlash(tp.SubResourceBaseTarget), rel)
 }
 
 func (l *genericResource) initContent() error {
@@ -484,102 +298,143 @@
 		}
 
 		l.content = string(b)
-
 	})
 
 	return err
 }
 
-func (l *genericResource) getSourceFs() afero.Fs {
-	return l.sourceFs
+func (l *genericResource) setName(name string) {
+	l.name = name
 }
 
-func (l *genericResource) publishIfNeeded() {
-	if l.publishOnce != nil {
-		l.publishOnce.publish(l)
-	}
+func (l *genericResource) getResourcePaths() *resourcePathDescriptor {
+	return l.resourcePathDescriptor
 }
 
-func (l *genericResource) Permalink() string {
-	l.publishIfNeeded()
-	return l.spec.PermalinkForBaseURL(l.relPermalinkForRel(l.relTargetDirFile.path(), true), l.spec.BaseURL.HostURL())
+func (l *genericResource) getSpec() *Spec {
+	return l.spec
 }
 
-func (l *genericResource) RelPermalink() string {
-	l.publishIfNeeded()
-	return l.relPermalinkFor(l.relTargetDirFile.path())
+func (l *genericResource) getTargetFilenames() []string {
+	paths := l.relTargetPaths()
+	for i, p := range paths {
+		paths[i] = filepath.Clean(p)
+	}
+	return paths
 }
 
-func (l *genericResource) Key() string {
-	return l.relTargetDirFile.path()
+func (l *genericResource) setTitle(title string) {
+	l.title = title
 }
 
-func (l *genericResource) relPermalinkFor(target string) string {
-	return l.relPermalinkForRel(target, false)
-
+func (r *genericResource) tryTransformedFileCache(key string, u *transformationUpdate) io.ReadCloser {
+	fi, f, meta, found := r.spec.ResourceCache.getFromFile(key)
+	if !found {
+		return nil
+	}
+	u.sourceFilename = &fi.Name
+	mt, _ := r.spec.MediaTypes.GetByType(meta.MediaTypeV)
+	u.mediaType = mt
+	u.data = meta.MetaData
+	u.targetPath = meta.Target
+	return f
 }
-func (l *genericResource) permalinkFor(target string) string {
-	return l.spec.PermalinkForBaseURL(l.relPermalinkForRel(target, true), l.spec.BaseURL.HostURL())
 
+func (r *genericResource) mergeData(in map[string]interface{}) {
+	if len(in) == 0 {
+		return
+	}
+	if r.data == nil {
+		r.data = make(map[string]interface{})
+	}
+	for k, v := range in {
+		if _, found := r.data[k]; !found {
+			r.data[k] = v
+		}
+	}
 }
-func (l *genericResource) relTargetPathsFor(target string) []string {
-	return l.relTargetPathsForRel(target)
-}
 
-func (l *genericResource) relTargetPaths() []string {
-	return l.relTargetPathsForRel(l.TargetPath())
-}
+func (rc *genericResource) cloneWithUpdates(u *transformationUpdate) (baseResource, error) {
+	r := rc.clone()
 
-func (l *genericResource) Name() string {
-	return l.name
-}
+	if u.content != nil {
+		r.contentInit.Do(func() {
+			r.content = *u.content
+			r.openReadSeekerCloser = func() (hugio.ReadSeekCloser, error) {
+				return hugio.NewReadSeekerNoOpCloserFromString(r.content), nil
+			}
+		})
+	}
 
-func (l *genericResource) Title() string {
-	return l.title
-}
+	r.mediaType = u.mediaType
 
-func (l *genericResource) Params() map[string]interface{} {
-	return l.params
-}
+	if u.sourceFilename != nil {
+		r.setSourceFilename(*u.sourceFilename)
+	}
 
-func (l *genericResource) setTitle(title string) {
-	l.title = title
+	if u.sourceFs != nil {
+		r.setSourceFs(u.sourceFs)
+	}
+
+	if u.targetPath == "" {
+		return nil, errors.New("missing targetPath")
+	}
+
+	fpath, fname := path.Split(u.targetPath)
+	r.resourcePathDescriptor.relTargetDirFile = dirFile{dir: fpath, file: fname}
+
+	r.mergeData(u.data)
+
+	return r, nil
 }
 
-func (l *genericResource) setName(name string) {
-	l.name = name
+func (l genericResource) clone() *genericResource {
+	gi := *l.resourceFileInfo
+	rp := *l.resourcePathDescriptor
+	l.resourceFileInfo = &gi
+	l.resourcePathDescriptor = &rp
+	l.resourceContent = &resourceContent{}
+	return &l
 }
 
-func (l *genericResource) updateParams(params map[string]interface{}) {
-	if l.params == nil {
-		l.params = params
-		return
-	}
+// returns an opened file or nil if nothing to write.
+func (l *genericResource) openDestinationsForWriting() (io.WriteCloser, error) {
+	targetFilenames := l.getTargetFilenames()
+	var changedFilenames []string
 
-	// Sets the params not already set
-	for k, v := range params {
-		if _, found := l.params[k]; !found {
-			l.params[k] = v
+	// Fast path:
+	// This is a processed version of the original;
+	// check if it already existis at the destination.
+	for _, targetFilename := range targetFilenames {
+		if _, err := l.getSpec().BaseFs.PublishFs.Stat(targetFilename); err == nil {
+			continue
 		}
+		changedFilenames = append(changedFilenames, targetFilename)
 	}
+
+	if len(changedFilenames) == 0 {
+		return nil, nil
+	}
+
+	return helpers.OpenFilesForWriting(l.getSpec().BaseFs.PublishFs, changedFilenames...)
 }
 
-func (l *genericResource) relPermalinkForRel(rel string, isAbs bool) string {
-	return l.spec.PathSpec.URLizeFilename(l.relTargetPathForRel(rel, false, isAbs, true))
+func (r *genericResource) openPublishFileForWriting(relTargetPath string) (io.WriteCloser, error) {
+	return helpers.OpenFilesForWriting(r.spec.BaseFs.PublishFs, r.relTargetPathsFor(relTargetPath)...)
 }
 
-func (l *genericResource) relTargetPathsForRel(rel string) []string {
-	if len(l.baseTargetPathDirs) == 0 {
-		return []string{l.relTargetPathForRelAndBasePath(rel, "", false, false)}
-	}
+func (l *genericResource) permalinkFor(target string) string {
+	return l.spec.PermalinkForBaseURL(l.relPermalinkForRel(target, true), l.spec.BaseURL.HostURL())
+}
 
-	var targetPaths = make([]string, len(l.baseTargetPathDirs))
-	for i, dir := range l.baseTargetPathDirs {
-		targetPaths[i] = l.relTargetPathForRelAndBasePath(rel, dir, false, false)
-	}
-	return targetPaths
+func (l *genericResource) relPermalinkFor(target string) string {
+	return l.relPermalinkForRel(target, false)
 }
 
+func (l *genericResource) relPermalinkForRel(rel string, isAbs bool) string {
+	return l.spec.PathSpec.URLizeFilename(l.relTargetPathForRel(rel, false, isAbs, true))
+}
+
 func (l *genericResource) relTargetPathForRel(rel string, addBaseTargetPath, isAbs, isURL bool) string {
 	if addBaseTargetPath && len(l.baseTargetPathDirs) > 1 {
 		panic("multiple baseTargetPathDirs")
@@ -592,20 +447,6 @@
 	return l.relTargetPathForRelAndBasePath(rel, basePath, isAbs, isURL)
 }
 
-func (l *genericResource) createBasePath(rel string, isURL bool) string {
-	if l.targetPathBuilder == nil {
-		return rel
-	}
-	tp := l.targetPathBuilder()
-
-	if isURL {
-		return path.Join(tp.SubResourceBaseLink, rel)
-	}
-
-	// TODO(bep) path
-	return path.Join(filepath.ToSlash(tp.SubResourceBaseTarget), rel)
-}
-
 func (l *genericResource) relTargetPathForRelAndBasePath(rel, basePath string, isAbs, isURL bool) string {
 	rel = l.createBasePath(rel, isURL)
 
@@ -631,117 +472,153 @@
 	return rel
 }
 
-func (l *genericResource) ResourceType() string {
-	return l.resourceType
+func (l *genericResource) relTargetPaths() []string {
+	return l.relTargetPathsForRel(l.TargetPath())
 }
 
-func (l *genericResource) String() string {
-	return fmt.Sprintf("Resource(%s: %s)", l.resourceType, l.name)
+func (l *genericResource) relTargetPathsFor(target string) []string {
+	return l.relTargetPathsForRel(target)
 }
 
-func (l *genericResource) Publish() error {
-	fr, err := l.ReadSeekCloser()
-	if err != nil {
-		return err
+func (l *genericResource) relTargetPathsForRel(rel string) []string {
+	if len(l.baseTargetPathDirs) == 0 {
+		return []string{l.relTargetPathForRelAndBasePath(rel, "", false, false)}
 	}
-	defer fr.Close()
 
-	fw, err := helpers.OpenFilesForWriting(l.spec.BaseFs.PublishFs, l.targetFilenames()...)
-	if err != nil {
-		return err
+	targetPaths := make([]string, len(l.baseTargetPathDirs))
+	for i, dir := range l.baseTargetPathDirs {
+		targetPaths[i] = l.relTargetPathForRelAndBasePath(rel, dir, false, false)
 	}
-	defer fw.Close()
-
-	_, err = io.Copy(fw, fr)
-	return err
+	return targetPaths
 }
 
-// Path is stored with Unix style slashes.
-func (l *genericResource) TargetPath() string {
-	return l.relTargetDirFile.path()
-}
+func (l *genericResource) updateParams(params map[string]interface{}) {
+	if l.params == nil {
+		l.params = params
+		return
+	}
 
-func (l *genericResource) targetFilenames() []string {
-	paths := l.relTargetPaths()
-	for i, p := range paths {
-		paths[i] = filepath.Clean(p)
+	// Sets the params not already set
+	for k, v := range params {
+		if _, found := l.params[k]; !found {
+			l.params[k] = v
+		}
 	}
-	return paths
 }
 
-// TODO(bep) clean up below
-func (r *Spec) newGenericResource(sourceFs afero.Fs,
-	targetPathBuilder func() page.TargetPaths,
-	osFileInfo os.FileInfo,
-	sourceFilename,
-	baseFilename string,
-	mediaType media.Type) *genericResource {
-	return r.newGenericResourceWithBase(
-		sourceFs,
-		false,
-		nil,
-		nil,
-		targetPathBuilder,
-		osFileInfo,
-		sourceFilename,
-		baseFilename,
-		mediaType,
-	)
+type targetPather interface {
+	TargetPath() string
+}
 
+type permalinker interface {
+	targetPather
+	permalinkFor(target string) string
+	relPermalinkFor(target string) string
+	relTargetPaths() []string
+	relTargetPathsFor(target string) []string
 }
 
-func (r *Spec) newGenericResourceWithBase(
-	sourceFs afero.Fs,
-	lazyPublish bool,
-	openReadSeekerCloser resource.OpenReadSeekCloser,
-	targetPathBaseDirs []string,
-	targetPathBuilder func() page.TargetPaths,
-	osFileInfo os.FileInfo,
-	sourceFilename,
-	baseFilename string,
-	mediaType media.Type) *genericResource {
+type resourceContent struct {
+	content     string
+	contentInit sync.Once
+}
 
-	if osFileInfo != nil && osFileInfo.IsDir() {
-		panic(fmt.Sprintf("dirs not supported resource types: %v", osFileInfo))
-	}
+type resourceFileInfo struct {
+	// Will be set if this resource is backed by something other than a file.
+	openReadSeekerCloser resource.OpenReadSeekCloser
 
-	// This value is used both to construct URLs and file paths, but start
-	// with a Unix-styled path.
-	baseFilename = helpers.ToSlashTrimLeading(baseFilename)
-	fpath, fname := path.Split(baseFilename)
+	// This may be set to tell us to look in another filesystem for this resource.
+	// We, by default, use the sourceFs filesystem in the spec below.
+	sourceFs afero.Fs
 
-	var resourceType string
-	if mediaType.MainType == "image" {
-		resourceType = mediaType.MainType
-	} else {
-		resourceType = mediaType.SubType
-	}
+	// Absolute filename to the source, including any content folder path.
+	// Note that this is absolute in relation to the filesystem it is stored in.
+	// It can be a base path filesystem, and then this filename will not match
+	// the path to the file on the real filesystem.
+	sourceFilename string
 
-	pathDescriptor := resourcePathDescriptor{
-		baseTargetPathDirs: helpers.UniqueStringsReuse(targetPathBaseDirs),
-		targetPathBuilder:  targetPathBuilder,
-		relTargetDirFile:   dirFile{dir: fpath, file: fname},
+	fi os.FileInfo
+
+	// A hash of the source content. Is only calculated in caching situations.
+	h *resourceHash
+}
+
+func (fi *resourceFileInfo) ReadSeekCloser() (hugio.ReadSeekCloser, error) {
+	if fi.openReadSeekerCloser != nil {
+		return fi.openReadSeekerCloser()
 	}
 
-	var po *publishOnce
-	if lazyPublish {
-		po = &publishOnce{logger: r.Logger}
+	f, err := fi.getSourceFs().Open(fi.getSourceFilename())
+	if err != nil {
+		return nil, err
 	}
+	return f, nil
+}
 
-	return &genericResource{
-		openReadSeekerCloser:   openReadSeekerCloser,
-		publishOnce:            po,
-		resourcePathDescriptor: pathDescriptor,
-		sourceFs:               sourceFs,
-		osFileInfo:             osFileInfo,
-		sourceFilename:         sourceFilename,
-		mediaType:              mediaType,
-		resourceType:           resourceType,
-		spec:                   r,
-		params:                 make(map[string]interface{}),
-		name:                   baseFilename,
-		title:                  baseFilename,
-		resourceContent:        &resourceContent{},
-		resourceHash:           &resourceHash{},
+func (fi *resourceFileInfo) getSourceFilename() string {
+	return fi.sourceFilename
+}
+
+func (fi *resourceFileInfo) setSourceFilename(s string) {
+	// Make sure it's always loaded by sourceFilename.
+	fi.openReadSeekerCloser = nil
+	fi.sourceFilename = s
+}
+
+func (fi *resourceFileInfo) getSourceFs() afero.Fs {
+	return fi.sourceFs
+}
+
+func (fi *resourceFileInfo) setSourceFs(fs afero.Fs) {
+	fi.sourceFs = fs
+}
+
+func (fi *resourceFileInfo) hash() (string, error) {
+	var err error
+	fi.h.init.Do(func() {
+		var hash string
+		var f hugio.ReadSeekCloser
+		f, err = fi.ReadSeekCloser()
+		if err != nil {
+			err = errors.Wrap(err, "failed to open source file")
+			return
+		}
+		defer f.Close()
+
+		hash, err = helpers.MD5FromFileFast(f)
+		if err != nil {
+			return
+		}
+		fi.h.value = hash
+	})
+
+	return fi.h.value, err
+}
+
+func (fi *resourceFileInfo) size() int {
+	if fi.fi == nil {
+		return 0
 	}
+
+	return int(fi.fi.Size())
+}
+
+type resourceHash struct {
+	value string
+	init  sync.Once
+}
+
+type resourcePathDescriptor struct {
+	// The relative target directory and filename.
+	relTargetDirFile dirFile
+
+	// Callback used to construct a target path relative to its owner.
+	targetPathBuilder func() page.TargetPaths
+
+	// This will normally be the same as above, but this will only apply to publishing
+	// of resources. It may be mulltiple values when in multihost mode.
+	baseTargetPathDirs []string
+
+	// baseOffset is set when the output format's path has a offset, e.g. for AMP.
+	baseOffset string
 }
--- a/resources/resource/resourcetypes.go
+++ b/resources/resource/resourcetypes.go
@@ -23,7 +23,7 @@
 // Cloner is an internal template and not meant for use in the templates. It
 // may change without notice.
 type Cloner interface {
-	WithNewBase(base string) Resource
+	Clone() Resource
 }
 
 // Resource represents a linkable resource, i.e. a content page, image etc.
@@ -35,6 +35,20 @@
 	ResourceDataProvider
 }
 
+// Image represents an image resource.
+type Image interface {
+	Resource
+	ImageOps
+}
+
+type ImageOps interface {
+	Height() int
+	Width() int
+	Fill(spec string) (Image, error)
+	Fit(spec string) (Image, error)
+	Resize(spec string) (Image, error)
+}
+
 type ResourceTypesProvider interface {
 	// MediaType is this resource's MIME type.
 	MediaType() media.Type
@@ -117,6 +131,10 @@
 // ReadSeekCloserResource is a Resource that supports loading its content.
 type ReadSeekCloserResource interface {
 	MediaType() media.Type
+	ReadSeekCloserProvider
+}
+
+type ReadSeekCloserProvider interface {
 	ReadSeekCloser() (hugio.ReadSeekCloser, error)
 }
 
--- a/resources/resource_cache.go
+++ b/resources/resource_cache.go
@@ -281,7 +281,7 @@
 
 	for k := range c.cache {
 		clear := false
-		for p, _ := range partitionsSet {
+		for p := range partitionsSet {
 			if strings.Contains(k, p) {
 				// There will be some false positive, but that's fine.
 				clear = true
--- a/resources/resource_metadata.go
+++ b/resources/resource_metadata.go
@@ -29,9 +29,15 @@
 )
 
 var (
-	_ metaAssigner = (*genericResource)(nil)
+	_ metaAssigner         = (*genericResource)(nil)
+	_ metaAssigner         = (*imageResource)(nil)
+	_ metaAssignerProvider = (*resourceAdapter)(nil)
 )
 
+type metaAssignerProvider interface {
+	getMetaAssigner() metaAssigner
+}
+
 // metaAssigner allows updating metadata in resources that supports it.
 type metaAssigner interface {
 	setTitle(title string)
@@ -50,8 +56,15 @@
 	counters := make(map[string]int)
 
 	for _, r := range resources {
-		if _, ok := r.(metaAssigner); !ok {
-			continue
+		var ma metaAssigner
+		mp, ok := r.(metaAssignerProvider)
+		if ok {
+			ma = mp.getMetaAssigner()
+		} else {
+			ma, ok = r.(metaAssigner)
+			if !ok {
+				continue
+			}
 		}
 
 		var (
@@ -61,7 +74,6 @@
 			resourceSrcKey                      = strings.ToLower(r.Name())
 		)
 
-		ma := r.(metaAssigner)
 		for _, meta := range metadata {
 			src, found := meta["src"]
 			if !found {
--- a/resources/resource_metadata_test.go
+++ b/resources/resource_metadata_test.go
@@ -24,7 +24,7 @@
 
 func TestAssignMetadata(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 
 	var foo1, foo2, foo3, logo1, logo2, logo3 resource.Resource
 	var resources resource.Resources
--- /dev/null
+++ b/resources/resource_spec.go
@@ -1,0 +1,304 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package resources
+
+import (
+	"errors"
+	"fmt"
+	"mime"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"github.com/gohugoio/hugo/helpers"
+
+	"github.com/gohugoio/hugo/cache/filecache"
+	"github.com/gohugoio/hugo/common/loggers"
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/output"
+	"github.com/gohugoio/hugo/resources/images"
+	"github.com/gohugoio/hugo/resources/page"
+	"github.com/gohugoio/hugo/resources/resource"
+	"github.com/gohugoio/hugo/tpl"
+	"github.com/spf13/afero"
+)
+
+func NewSpec(
+	s *helpers.PathSpec,
+	fileCaches filecache.Caches,
+	logger *loggers.Logger,
+	outputFormats output.Formats,
+	mimeTypes media.Types) (*Spec, error) {
+
+	imgConfig, err := images.DecodeConfig(s.Cfg.GetStringMap("imaging"))
+	if err != nil {
+		return nil, err
+	}
+
+	imaging := &images.ImageProcessor{Cfg: imgConfig}
+
+	if logger == nil {
+		logger = loggers.NewErrorLogger()
+	}
+
+	permalinks, err := page.NewPermalinkExpander(s)
+	if err != nil {
+		return nil, err
+	}
+
+	rs := &Spec{PathSpec: s,
+		Logger:        logger,
+		imaging:       imaging,
+		MediaTypes:    mimeTypes,
+		OutputFormats: outputFormats,
+		Permalinks:    permalinks,
+		FileCaches:    fileCaches,
+		imageCache: newImageCache(
+			fileCaches.ImageCache(),
+
+			s,
+		)}
+
+	rs.ResourceCache = newResourceCache(rs)
+
+	return rs, nil
+
+}
+
+type Spec struct {
+	*helpers.PathSpec
+
+	MediaTypes    media.Types
+	OutputFormats output.Formats
+
+	Logger *loggers.Logger
+
+	TextTemplates tpl.TemplateParseFinder
+
+	Permalinks page.PermalinkExpander
+
+	// Holds default filter settings etc.
+	imaging *images.ImageProcessor
+
+	imageCache    *imageCache
+	ResourceCache *ResourceCache
+	FileCaches    filecache.Caches
+}
+
+func (r *Spec) New(fd ResourceSourceDescriptor) (resource.Resource, error) {
+	return r.newResourceFor(fd)
+}
+
+func (r *Spec) CacheStats() string {
+	r.imageCache.mu.RLock()
+	defer r.imageCache.mu.RUnlock()
+
+	s := fmt.Sprintf("Cache entries: %d", len(r.imageCache.store))
+
+	count := 0
+	for k := range r.imageCache.store {
+		if count > 5 {
+			break
+		}
+		s += "\n" + k
+		count++
+	}
+
+	return s
+}
+
+func (r *Spec) ClearCaches() {
+	r.imageCache.clear()
+	r.ResourceCache.clear()
+}
+
+func (r *Spec) DeleteCacheByPrefix(prefix string) {
+	r.imageCache.deleteByPrefix(prefix)
+}
+
+// TODO(bep) unify
+func (r *Spec) IsInImageCache(key string) bool {
+	// This is used for cache pruning. We currently only have images, but we could
+	// imagine expanding on this.
+	return r.imageCache.isInCache(key)
+}
+
+func (s *Spec) String() string {
+	return "spec"
+}
+
+// TODO(bep) clean up below
+func (r *Spec) newGenericResource(sourceFs afero.Fs,
+	targetPathBuilder func() page.TargetPaths,
+	osFileInfo os.FileInfo,
+	sourceFilename,
+	baseFilename string,
+	mediaType media.Type) *genericResource {
+	return r.newGenericResourceWithBase(
+		sourceFs,
+		nil,
+		nil,
+		targetPathBuilder,
+		osFileInfo,
+		sourceFilename,
+		baseFilename,
+		mediaType,
+	)
+
+}
+
+func (r *Spec) newGenericResourceWithBase(
+	sourceFs afero.Fs,
+	openReadSeekerCloser resource.OpenReadSeekCloser,
+	targetPathBaseDirs []string,
+	targetPathBuilder func() page.TargetPaths,
+	osFileInfo os.FileInfo,
+	sourceFilename,
+	baseFilename string,
+	mediaType media.Type) *genericResource {
+
+	if osFileInfo != nil && osFileInfo.IsDir() {
+		panic(fmt.Sprintf("dirs not supported resource types: %v", osFileInfo))
+	}
+
+	// This value is used both to construct URLs and file paths, but start
+	// with a Unix-styled path.
+	baseFilename = helpers.ToSlashTrimLeading(baseFilename)
+	fpath, fname := path.Split(baseFilename)
+
+	var resourceType string
+	if mediaType.MainType == "image" {
+		resourceType = mediaType.MainType
+	} else {
+		resourceType = mediaType.SubType
+	}
+
+	pathDescriptor := &resourcePathDescriptor{
+		baseTargetPathDirs: helpers.UniqueStringsReuse(targetPathBaseDirs),
+		targetPathBuilder:  targetPathBuilder,
+		relTargetDirFile:   dirFile{dir: fpath, file: fname},
+	}
+
+	gfi := &resourceFileInfo{
+		fi:                   osFileInfo,
+		openReadSeekerCloser: openReadSeekerCloser,
+		sourceFs:             sourceFs,
+		sourceFilename:       sourceFilename,
+		h:                    &resourceHash{},
+	}
+
+	g := &genericResource{
+		resourceFileInfo:       gfi,
+		resourcePathDescriptor: pathDescriptor,
+		mediaType:              mediaType,
+		resourceType:           resourceType,
+		spec:                   r,
+		params:                 make(map[string]interface{}),
+		name:                   baseFilename,
+		title:                  baseFilename,
+		resourceContent:        &resourceContent{},
+	}
+
+	return g
+
+}
+
+func (r *Spec) newResource(sourceFs afero.Fs, fd ResourceSourceDescriptor) (resource.Resource, error) {
+	fi := fd.FileInfo
+	var sourceFilename string
+
+	if fd.OpenReadSeekCloser != nil {
+	} else if fd.SourceFilename != "" {
+		var err error
+		fi, err = sourceFs.Stat(fd.SourceFilename)
+		if err != nil {
+			if os.IsNotExist(err) {
+				return nil, nil
+			}
+			return nil, err
+		}
+		sourceFilename = fd.SourceFilename
+	} else {
+		sourceFilename = fd.SourceFile.Filename()
+	}
+
+	if fd.RelTargetFilename == "" {
+		fd.RelTargetFilename = sourceFilename
+	}
+
+	ext := strings.ToLower(filepath.Ext(fd.RelTargetFilename))
+	mimeType, found := r.MediaTypes.GetFirstBySuffix(strings.TrimPrefix(ext, "."))
+	// TODO(bep) we need to handle these ambigous types better, but in this context
+	// we most likely want the application/xml type.
+	if mimeType.Suffix() == "xml" && mimeType.SubType == "rss" {
+		mimeType, found = r.MediaTypes.GetByType("application/xml")
+	}
+
+	if !found {
+		// A fallback. Note that mime.TypeByExtension is slow by Hugo standards,
+		// so we should configure media types to avoid this lookup for most
+		// situations.
+		mimeStr := mime.TypeByExtension(ext)
+		if mimeStr != "" {
+			mimeType, _ = media.FromStringAndExt(mimeStr, ext)
+		}
+	}
+
+	gr := r.newGenericResourceWithBase(
+		sourceFs,
+		fd.OpenReadSeekCloser,
+		fd.TargetBasePaths,
+		fd.TargetPaths,
+		fi,
+		sourceFilename,
+		fd.RelTargetFilename,
+		mimeType)
+
+	if mimeType.MainType == "image" {
+		imgFormat, ok := images.ImageFormatFromExt(ext)
+		if ok {
+			ir := &imageResource{
+				Image:        images.NewImage(imgFormat, r.imaging, nil, gr),
+				baseResource: gr,
+			}
+			return newResourceAdapter(gr.spec, fd.LazyPublish, ir), nil
+		}
+
+	}
+
+	return newResourceAdapter(gr.spec, fd.LazyPublish, gr), nil
+
+}
+
+func (r *Spec) newResourceFor(fd ResourceSourceDescriptor) (resource.Resource, error) {
+	if fd.OpenReadSeekCloser == nil {
+		if fd.SourceFile != nil && fd.SourceFilename != "" {
+			return nil, errors.New("both SourceFile and AbsSourceFilename provided")
+		} else if fd.SourceFile == nil && fd.SourceFilename == "" {
+			return nil, errors.New("either SourceFile or AbsSourceFilename must be provided")
+		}
+	}
+
+	if fd.RelTargetFilename == "" {
+		fd.RelTargetFilename = fd.Filename()
+	}
+
+	if len(fd.TargetBasePaths) == 0 {
+		// If not set, we publish the same resource to all hosts.
+		fd.TargetBasePaths = r.MultihostTargetBasePaths
+	}
+
+	return r.newResource(fd.Fs, fd)
+}
--- a/resources/resource_test.go
+++ b/resources/resource_test.go
@@ -32,7 +32,7 @@
 
 func TestGenericResource(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 
 	r := spec.newGenericResource(nil, nil, nil, "/a/foo.css", "foo.css", media.CSSType)
 
@@ -44,7 +44,7 @@
 
 func TestGenericResourceWithLinkFacory(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 
 	factory := newTargetPaths("/foo")
 
@@ -58,7 +58,7 @@
 
 func TestNewResourceFromFilename(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 
 	writeSource(t, spec.Fs, "content/a/b/logo.png", "image")
 	writeSource(t, spec.Fs, "content/a/b/data.json", "json")
@@ -79,14 +79,11 @@
 	c.Assert(r, qt.Not(qt.IsNil))
 	c.Assert(r.ResourceType(), qt.Equals, "json")
 
-	cloned := r.(resource.Cloner).WithNewBase("aceof")
-	c.Assert(cloned.ResourceType(), qt.Equals, r.ResourceType())
-	c.Assert(cloned.RelPermalink(), qt.Equals, "/aceof/a/b/data.json")
 }
 
 func TestNewResourceFromFilenameSubPathInBaseURL(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpecForBaseURL(c, "https://example.com/docs")
+	spec := newTestResourceSpec(specDescriptor{c: c, baseURL: "https://example.com/docs"})
 
 	writeSource(t, spec.Fs, "content/a/b/logo.png", "image")
 	bfs := afero.NewBasePathFs(spec.Fs.Source, "content")
@@ -99,8 +96,6 @@
 	c.Assert(r.ResourceType(), qt.Equals, "image")
 	c.Assert(r.RelPermalink(), qt.Equals, "/docs/a/b/logo.png")
 	c.Assert(r.Permalink(), qt.Equals, "https://example.com/docs/a/b/logo.png")
-	img := r.(*Image)
-	c.Assert(img.targetFilenames()[0], qt.Equals, filepath.FromSlash("/a/b/logo.png"))
 
 }
 
@@ -108,7 +103,7 @@
 
 func TestResourcesByType(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	resources := resource.Resources{
 		spec.newGenericResource(nil, nil, nil, "/a/foo1.css", "foo1.css", media.CSSType),
 		spec.newGenericResource(nil, nil, nil, "/a/logo.png", "logo.css", pngType),
@@ -122,7 +117,7 @@
 
 func TestResourcesGetByPrefix(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	resources := resource.Resources{
 		spec.newGenericResource(nil, nil, nil, "/a/foo1.css", "foo1.css", media.CSSType),
 		spec.newGenericResource(nil, nil, nil, "/a/logo1.png", "logo1.png", pngType),
@@ -151,7 +146,7 @@
 
 func TestResourcesGetMatch(t *testing.T) {
 	c := qt.New(t)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	resources := resource.Resources{
 		spec.newGenericResource(nil, nil, nil, "/a/foo1.css", "foo1.css", media.CSSType),
 		spec.newGenericResource(nil, nil, nil, "/a/logo1.png", "logo1.png", pngType),
@@ -213,7 +208,7 @@
 // my own curiosity.
 func BenchmarkResourcesMatchA100(b *testing.B) {
 	c := qt.New(b)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	a100 := strings.Repeat("a", 100)
 	pattern := "a*a*a*a*a*a*a*a*b"
 
@@ -228,7 +223,7 @@
 
 func benchResources(b *testing.B) resource.Resources {
 	c := qt.New(b)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	var resources resource.Resources
 
 	for i := 0; i < 30; i++ {
@@ -252,7 +247,7 @@
 
 func BenchmarkAssignMetadata(b *testing.B) {
 	c := qt.New(b)
-	spec := newTestResourceSpec(c)
+	spec := newTestResourceSpec(specDescriptor{c: c})
 
 	for i := 0; i < b.N; i++ {
 		b.StopTimer()
--- /dev/null
+++ b/resources/resource_transformers/htesting/testhelpers.go
@@ -1,0 +1,80 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package htesting
+
+import (
+	"path/filepath"
+
+	"github.com/gohugoio/hugo/cache/filecache"
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/output"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/spf13/afero"
+	"github.com/spf13/viper"
+)
+
+func NewTestResourceSpec() (*resources.Spec, error) {
+	cfg := viper.New()
+	cfg.Set("baseURL", "https://example.org")
+	cfg.Set("publishDir", "public")
+
+	imagingCfg := map[string]interface{}{
+		"resampleFilter": "linear",
+		"quality":        68,
+		"anchor":         "left",
+	}
+
+	cfg.Set("imaging", imagingCfg)
+
+	fs := hugofs.NewMem(cfg)
+
+	s, err := helpers.NewPathSpec(fs, cfg, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	filecaches, err := filecache.NewCaches(s)
+	if err != nil {
+		return nil, err
+	}
+
+	spec, err := resources.NewSpec(s, filecaches, nil, output.DefaultFormats, media.DefaultTypes)
+	return spec, err
+}
+
+func NewResourceTransformer(filename, content string) (resources.ResourceTransformer, error) {
+	spec, err := NewTestResourceSpec()
+	if err != nil {
+		return nil, err
+	}
+	return NewResourceTransformerForSpec(spec, filename, content)
+}
+
+func NewResourceTransformerForSpec(spec *resources.Spec, filename, content string) (resources.ResourceTransformer, error) {
+	filename = filepath.FromSlash(filename)
+
+	fs := spec.Fs.Source
+	if err := afero.WriteFile(fs, filename, []byte(content), 0777); err != nil {
+		return nil, err
+	}
+
+	r, err := spec.New(resources.ResourceSourceDescriptor{Fs: fs, SourceFilename: filename})
+	if err != nil {
+		return nil, err
+	}
+
+	return r.(resources.ResourceTransformer), nil
+}
--- a/resources/resource_transformers/integrity/integrity.go
+++ b/resources/resource_transformers/integrity/integrity.go
@@ -23,6 +23,8 @@
 	"html/template"
 	"io"
 
+	"github.com/gohugoio/hugo/resources/internal"
+
 	"github.com/pkg/errors"
 
 	"github.com/gohugoio/hugo/resources"
@@ -46,8 +48,8 @@
 	algo string
 }
 
-func (t *fingerprintTransformation) Key() resources.ResourceTransformationKey {
-	return resources.NewResourceTransformationKey("fingerprint", t.algo)
+func (t *fingerprintTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("fingerprint", t.algo)
 }
 
 // Transform creates a MD5 hash of the Resource content and inserts that hash before
@@ -59,7 +61,17 @@
 		return err
 	}
 
-	io.Copy(io.MultiWriter(h, ctx.To), ctx.From)
+	var w io.Writer
+	if rc, ok := ctx.From.(io.ReadSeeker); ok {
+		// This transformation does not change the content, so try to
+		// avoid writing to To if we can.
+		defer rc.Seek(0, 0)
+		w = h
+	} else {
+		w = io.MultiWriter(h, ctx.To)
+	}
+
+	io.Copy(w, ctx.From)
 	d, err := digest(h)
 	if err != nil {
 		return err
@@ -91,15 +103,12 @@
 // the base64-encoded Subresource Integrity hash, so you will have to stay away from
 // md5 if you plan to use both.
 // See https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
-func (c *Client) Fingerprint(res resource.Resource, algo string) (resource.Resource, error) {
+func (c *Client) Fingerprint(res resources.ResourceTransformer, algo string) (resource.Resource, error) {
 	if algo == "" {
 		algo = defaultHashAlgo
 	}
 
-	return c.rs.Transform(
-		res,
-		&fingerprintTransformation{algo: algo},
-	)
+	return res.Transform(&fingerprintTransformation{algo: algo})
 }
 
 func integrity(algo string, sum []byte) template.HTMLAttr {
--- a/resources/resource_transformers/integrity/integrity_test.go
+++ b/resources/resource_transformers/integrity/integrity_test.go
@@ -14,9 +14,13 @@
 package integrity
 
 import (
+	"html/template"
 	"testing"
 
+	"github.com/gohugoio/hugo/resources/resource"
+
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/resources/resource_transformers/htesting"
 )
 
 func TestHashFromAlgo(t *testing.T) {
@@ -45,4 +49,24 @@
 
 		})
 	}
+}
+
+func TestTransform(t *testing.T) {
+	c := qt.New(t)
+
+	spec, err := htesting.NewTestResourceSpec()
+	c.Assert(err, qt.IsNil)
+	client := New(spec)
+
+	r, err := htesting.NewResourceTransformerForSpec(spec, "hugo.txt", "Hugo Rocks!")
+	c.Assert(err, qt.IsNil)
+
+	transformed, err := client.Fingerprint(r, "")
+
+	c.Assert(err, qt.IsNil)
+	c.Assert(transformed.RelPermalink(), qt.Equals, "/hugo.a5ad1c6961214a55de53c1ce6e60d27b6b761f54851fa65e33066460dfa6a0db.txt")
+	c.Assert(transformed.Data(), qt.DeepEquals, map[string]interface{}{"Integrity": template.HTMLAttr("sha256-pa0caWEhSlXeU8HObmDSe2t2H1SFH6ZeMwZkYN+moNs=")})
+	content, err := transformed.(resource.ContentProvider).Content()
+	c.Assert(err, qt.IsNil)
+	c.Assert(content, qt.Equals, "Hugo Rocks!")
 }
--- a/resources/resource_transformers/minifier/minify.go
+++ b/resources/resource_transformers/minifier/minify.go
@@ -16,6 +16,7 @@
 import (
 	"github.com/gohugoio/hugo/minifiers"
 	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/internal"
 	"github.com/gohugoio/hugo/resources/resource"
 )
 
@@ -37,8 +38,8 @@
 	m  minifiers.Client
 }
 
-func (t *minifyTransformation) Key() resources.ResourceTransformationKey {
-	return resources.NewResourceTransformationKey("minify")
+func (t *minifyTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("minify")
 }
 
 func (t *minifyTransformation) Transform(ctx *resources.ResourceTransformationCtx) error {
@@ -49,11 +50,10 @@
 	return nil
 }
 
-func (c *Client) Minify(res resource.Resource) (resource.Resource, error) {
-	return c.rs.Transform(
-		res,
-		&minifyTransformation{
-			rs: c.rs,
-			m:  c.m},
-	)
+func (c *Client) Minify(res resources.ResourceTransformer) (resource.Resource, error) {
+	return res.Transform(&minifyTransformation{
+		rs: c.rs,
+		m:  c.m,
+	})
+
 }
--- /dev/null
+++ b/resources/resource_transformers/minifier/minify_test.go
@@ -1,0 +1,43 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package minifier
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/resources/resource"
+
+	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/resources/resource_transformers/htesting"
+)
+
+func TestTransform(t *testing.T) {
+	c := qt.New(t)
+
+	spec, err := htesting.NewTestResourceSpec()
+	c.Assert(err, qt.IsNil)
+	client := New(spec)
+
+	r, err := htesting.NewResourceTransformerForSpec(spec, "hugo.html", "<h1>   Hugo Rocks!   </h1>")
+	c.Assert(err, qt.IsNil)
+
+	transformed, err := client.Minify(r)
+	c.Assert(err, qt.IsNil)
+
+	c.Assert(transformed.RelPermalink(), qt.Equals, "/hugo.min.html")
+	content, err := transformed.(resource.ContentProvider).Content()
+	c.Assert(err, qt.IsNil)
+	c.Assert(content, qt.Equals, "<h1>Hugo Rocks!</h1>")
+
+}
--- a/resources/resource_transformers/postcss/postcss.go
+++ b/resources/resource_transformers/postcss/postcss.go
@@ -17,6 +17,7 @@
 	"io"
 	"path/filepath"
 
+	"github.com/gohugoio/hugo/resources/internal"
 	"github.com/spf13/cast"
 
 	"github.com/gohugoio/hugo/hugofs"
@@ -98,8 +99,8 @@
 	rs      *resources.Spec
 }
 
-func (t *postcssTransformation) Key() resources.ResourceTransformationKey {
-	return resources.NewResourceTransformationKey("postcss", t.options)
+func (t *postcssTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("postcss", t.options)
 }
 
 // Transform shells out to postcss-cli to do the heavy lifting.
@@ -187,9 +188,6 @@
 }
 
 // Process transforms the given Resource with the PostCSS processor.
-func (c *Client) Process(res resource.Resource, options Options) (resource.Resource, error) {
-	return c.rs.Transform(
-		res,
-		&postcssTransformation{rs: c.rs, options: options},
-	)
+func (c *Client) Process(res resources.ResourceTransformer, options Options) (resource.Resource, error) {
+	return res.Transform(&postcssTransformation{rs: c.rs, options: options})
 }
--- a/resources/resource_transformers/templates/execute_as_template.go
+++ b/resources/resource_transformers/templates/execute_as_template.go
@@ -17,6 +17,7 @@
 import (
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/internal"
 	"github.com/gohugoio/hugo/resources/resource"
 	"github.com/gohugoio/hugo/tpl"
 	"github.com/pkg/errors"
@@ -47,8 +48,8 @@
 	data         interface{}
 }
 
-func (t *executeAsTemplateTransform) Key() resources.ResourceTransformationKey {
-	return resources.NewResourceTransformationKey("execute-as-template", t.targetPath)
+func (t *executeAsTemplateTransform) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("execute-as-template", t.targetPath)
 }
 
 func (t *executeAsTemplateTransform) Transform(ctx *resources.ResourceTransformationCtx) error {
@@ -63,14 +64,11 @@
 	return templ.Execute(ctx.To, t.data)
 }
 
-func (c *Client) ExecuteAsTemplate(res resource.Resource, targetPath string, data interface{}) (resource.Resource, error) {
-	return c.rs.Transform(
-		res,
-		&executeAsTemplateTransform{
-			rs:           c.rs,
-			targetPath:   helpers.ToSlashTrimLeading(targetPath),
-			textTemplate: c.textTemplate,
-			data:         data,
-		},
-	)
+func (c *Client) ExecuteAsTemplate(res resources.ResourceTransformer, targetPath string, data interface{}) (resource.Resource, error) {
+	return res.Transform(&executeAsTemplateTransform{
+		rs:           c.rs,
+		targetPath:   helpers.ToSlashTrimLeading(targetPath),
+		textTemplate: c.textTemplate,
+		data:         data,
+	})
 }
--- a/resources/resource_transformers/tocss/scss/client.go
+++ b/resources/resource_transformers/tocss/scss/client.go
@@ -18,6 +18,7 @@
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/gohugoio/hugo/hugolib/filesystems"
 	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/internal"
 	"github.com/gohugoio/hugo/resources/resource"
 	"github.com/spf13/afero"
 
@@ -68,7 +69,7 @@
 	to scss.Options
 }
 
-func (c *Client) ToCSS(res resource.Resource, opts Options) (resource.Resource, error) {
+func (c *Client) ToCSS(res resources.ResourceTransformer, opts Options) (resource.Resource, error) {
 	internalOptions := options{
 		from: opts,
 	}
@@ -83,10 +84,7 @@
 		internalOptions.to.Precision = 8
 	}
 
-	return c.rs.Transform(
-		res,
-		&toCSSTransformation{c: c, options: internalOptions},
-	)
+	return res.Transform(&toCSSTransformation{c: c, options: internalOptions})
 }
 
 type toCSSTransformation struct {
@@ -94,8 +92,8 @@
 	options options
 }
 
-func (t *toCSSTransformation) Key() resources.ResourceTransformationKey {
-	return resources.NewResourceTransformationKey("tocss", t.options.from)
+func (t *toCSSTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("tocss", t.options.from)
 }
 
 func DecodeOptions(m map[string]interface{}) (opts Options, err error) {
--- a/resources/smartcrop.go
+++ /dev/null
@@ -1,77 +1,0 @@
-// Copyright 2019 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package resources
-
-import (
-	"image"
-
-	"github.com/disintegration/imaging"
-	"github.com/muesli/smartcrop"
-)
-
-const (
-	// Do not change.
-	smartCropIdentifier = "smart"
-
-	// This is just a increment, starting on 1. If Smart Crop improves its cropping, we
-	// need a way to trigger a re-generation of the crops in the wild, so increment this.
-	smartCropVersionNumber = 1
-)
-
-// Needed by smartcrop
-type imagingResizer struct {
-	filter imaging.ResampleFilter
-}
-
-func (r imagingResizer) Resize(img image.Image, width, height uint) image.Image {
-	return imaging.Resize(img, int(width), int(height), r.filter)
-}
-
-func newSmartCropAnalyzer(filter imaging.ResampleFilter) smartcrop.Analyzer {
-	return smartcrop.NewAnalyzer(imagingResizer{filter: filter})
-}
-
-func smartCrop(img image.Image, width, height int, anchor imaging.Anchor, filter imaging.ResampleFilter) (*image.NRGBA, error) {
-
-	if width <= 0 || height <= 0 {
-		return &image.NRGBA{}, nil
-	}
-
-	srcBounds := img.Bounds()
-	srcW := srcBounds.Dx()
-	srcH := srcBounds.Dy()
-
-	if srcW <= 0 || srcH <= 0 {
-		return &image.NRGBA{}, nil
-	}
-
-	if srcW == width && srcH == height {
-		return imaging.Clone(img), nil
-	}
-
-	smart := newSmartCropAnalyzer(filter)
-
-	rect, err := smart.FindBestCrop(img, width, height)
-
-	if err != nil {
-		return nil, err
-	}
-
-	b := img.Bounds().Intersect(rect)
-
-	cropped := imaging.Crop(img, b)
-
-	return imaging.Resize(cropped, width, height, filter), nil
-
-}
--- a/resources/testhelpers_test.go
+++ b/resources/testhelpers_test.go
@@ -4,8 +4,6 @@
 	"path/filepath"
 	"testing"
 
-	"github.com/gohugoio/hugo/htesting/hqt"
-
 	"image"
 	"io"
 	"io/ioutil"
@@ -28,8 +26,10 @@
 	"github.com/spf13/viper"
 )
 
-func newTestResourceSpec(c *qt.C) *Spec {
-	return newTestResourceSpecForBaseURL(c, "https://example.com/")
+type specDescriptor struct {
+	baseURL string
+	c       *qt.C
+	fs      afero.Fs
 }
 
 func createTestCfg() *viper.Viper {
@@ -54,7 +54,20 @@
 
 }
 
-func newTestResourceSpecForBaseURL(c *qt.C, baseURL string) *Spec {
+func newTestResourceSpec(desc specDescriptor) *Spec {
+
+	baseURL := desc.baseURL
+	if baseURL == "" {
+		baseURL = "https://example.com/"
+	}
+
+	afs := desc.fs
+	if afs == nil {
+		afs = afero.NewMemMapFs()
+	}
+
+	c := desc.c
+
 	cfg := createTestCfg()
 	cfg.Set("baseURL", baseURL)
 
@@ -66,7 +79,8 @@
 
 	cfg.Set("imaging", imagingCfg)
 
-	fs := hugofs.NewMem(cfg)
+	fs := hugofs.NewFrom(afs, cfg)
+	fs.Destination = hugofs.NewCreateCountingFs(fs.Destination)
 
 	s, err := helpers.NewPathSpec(fs, cfg, nil)
 	c.Assert(err, qt.IsNil)
@@ -117,19 +131,23 @@
 
 }
 
-func fetchSunset(c *qt.C) *Image {
+func fetchSunset(c *qt.C) resource.Image {
 	return fetchImage(c, "sunset.jpg")
 }
 
-func fetchImage(c *qt.C, name string) *Image {
-	spec := newTestResourceSpec(c)
+func fetchImage(c *qt.C, name string) resource.Image {
+	spec := newTestResourceSpec(specDescriptor{c: c})
 	return fetchImageForSpec(spec, c, name)
 }
-
-func fetchImageForSpec(spec *Spec, c *qt.C, name string) *Image {
+func fetchImageForSpec(spec *Spec, c *qt.C, name string) resource.Image {
 	r := fetchResourceForSpec(spec, c, name)
-	c.Assert(r, hqt.IsSameType, &Image{})
-	return r.(*Image)
+
+	img := r.(resource.Image)
+
+	c.Assert(img, qt.Not(qt.IsNil))
+	c.Assert(img.(specProvider).getSpec(), qt.Not(qt.IsNil))
+
+	return img
 }
 
 func fetchResourceForSpec(spec *Spec, c *qt.C, name string) resource.ContentResource {
--- a/resources/transform.go
+++ b/resources/transform.go
@@ -15,45 +15,63 @@
 
 import (
 	"bytes"
+	"fmt"
+	"io"
 	"path"
-	"strconv"
 	"strings"
+	"sync"
 
-	"github.com/pkg/errors"
+	"github.com/spf13/afero"
 
-	"github.com/gohugoio/hugo/common/collections"
+	bp "github.com/gohugoio/hugo/bufferpool"
+
+	"github.com/gohugoio/hugo/resources/internal"
+
 	"github.com/gohugoio/hugo/common/herrors"
 	"github.com/gohugoio/hugo/common/hugio"
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/gohugoio/hugo/resources/resource"
-	"github.com/mitchellh/hashstructure"
 
-	"fmt"
-	"io"
-	"sync"
-
 	"github.com/gohugoio/hugo/media"
-
-	bp "github.com/gohugoio/hugo/bufferpool"
 )
 
 var (
-	_ resource.ContentResource        = (*transformedResource)(nil)
-	_ resource.ReadSeekCloserResource = (*transformedResource)(nil)
-	_ collections.Slicer              = (*transformedResource)(nil)
-	_ resource.Identifier             = (*transformedResource)(nil)
+	_ resource.ContentResource        = (*resourceAdapter)(nil)
+	_ resource.ReadSeekCloserResource = (*resourceAdapter)(nil)
+	_ resource.Resource               = (*resourceAdapter)(nil)
+	_ resource.Source                 = (*resourceAdapter)(nil)
+	_ resource.Identifier             = (*resourceAdapter)(nil)
+	_ resource.ResourceMetaProvider   = (*resourceAdapter)(nil)
 )
 
-func (s *Spec) Transform(r resource.Resource, t ResourceTransformation) (resource.Resource, error) {
-	if r == nil {
-		return nil, errors.New("got nil Resource in transformation. Make sure you check with 'with' or 'if' when you get a resource, e.g. with resources.Get.")
+// These are transformations that need special support in Hugo that may not
+// be available when building the theme/site so we write the transformation
+// result to disk and reuse if needed for these,
+var transformationsToCacheOnDisk = map[string]bool{
+	"postcss": true,
+	"tocss":   true,
+}
+
+func newResourceAdapter(spec *Spec, lazyPublish bool, target transformableResource) *resourceAdapter {
+	var po *publishOnce
+	if lazyPublish {
+		po = &publishOnce{}
 	}
+	return &resourceAdapter{
+		resourceTransformations: &resourceTransformations{},
+		resourceAdapterInner: &resourceAdapterInner{
+			spec:        spec,
+			publishOnce: po,
+			target:      target,
+		},
+	}
+}
 
-	return &transformedResource{
-		Resource:                    r,
-		transformation:              t,
-		transformedResourceMetadata: transformedResourceMetadata{MetaData: make(map[string]interface{})},
-		cache:                       s.ResourceCache}, nil
+// ResourceTransformation is the interface that a resource transformation step
+// needs to implement.
+type ResourceTransformation interface {
+	Key() internal.ResourceTransformationKey
+	Transform(ctx *ResourceTransformationCtx) error
 }
 
 type ResourceTransformationCtx struct {
@@ -95,20 +113,6 @@
 	ctx.OutPath = ctx.addPathIdentifier(ctx.InPath, identifier)
 }
 
-func (ctx *ResourceTransformationCtx) addPathIdentifier(inPath, identifier string) string {
-	dir, file := path.Split(inPath)
-	base, ext := helpers.PathAndExt(file)
-	return path.Join(dir, (base + identifier + ext))
-}
-
-// ReplaceOutPathExtension transforming InPath to OutPath replacing the file
-// extension, e.g. ".scss"
-func (ctx *ResourceTransformationCtx) ReplaceOutPathExtension(newExt string) {
-	dir, file := path.Split(ctx.InPath)
-	base, _ := helpers.PathAndExt(file)
-	ctx.OutPath = path.Join(dir, (base + newExt))
-}
-
 // PublishSourceMap writes the content to the target folder of the main resource
 // with the ".map" extension added.
 func (ctx *ResourceTransformationCtx) PublishSourceMap(content string) error {
@@ -122,240 +126,198 @@
 	return err
 }
 
-// ResourceTransformationKey are provided by the different transformation implementations.
-// It identifies the transformation (name) and its configuration (elements).
-// We combine this in a chain with the rest of the transformations
-// with the target filename and a content hash of the origin to use as cache key.
-type ResourceTransformationKey struct {
-	name     string
-	elements []interface{}
+// ReplaceOutPathExtension transforming InPath to OutPath replacing the file
+// extension, e.g. ".scss"
+func (ctx *ResourceTransformationCtx) ReplaceOutPathExtension(newExt string) {
+	dir, file := path.Split(ctx.InPath)
+	base, _ := helpers.PathAndExt(file)
+	ctx.OutPath = path.Join(dir, (base + newExt))
 }
 
-// NewResourceTransformationKey creates a new ResourceTransformationKey from the transformation
-// name and elements. We will create a 64 bit FNV hash from the elements, which when combined
-// with the other key elements should be unique for all practical applications.
-func NewResourceTransformationKey(name string, elements ...interface{}) ResourceTransformationKey {
-	return ResourceTransformationKey{name: name, elements: elements}
+func (ctx *ResourceTransformationCtx) addPathIdentifier(inPath, identifier string) string {
+	dir, file := path.Split(inPath)
+	base, ext := helpers.PathAndExt(file)
+	return path.Join(dir, (base + identifier + ext))
 }
 
-// Do not change this without good reasons.
-func (k ResourceTransformationKey) key() string {
-	if len(k.elements) == 0 {
-		return k.name
-	}
+type publishOnce struct {
+	publisherInit sync.Once
+	publisherErr  error
+}
 
-	sb := bp.GetBuffer()
-	defer bp.PutBuffer(sb)
+type resourceAdapter struct {
+	commonResource
+	*resourceTransformations
+	*resourceAdapterInner
+}
 
-	sb.WriteString(k.name)
-	for _, element := range k.elements {
-		hash, err := hashstructure.Hash(element, nil)
-		if err != nil {
-			panic(err)
-		}
-		sb.WriteString("_")
-		sb.WriteString(strconv.FormatUint(hash, 10))
+func (r *resourceAdapter) Content() (interface{}, error) {
+	r.init(false, true)
+	if r.transformationsErr != nil {
+		return nil, r.transformationsErr
 	}
+	return r.target.Content()
+}
 
-	return sb.String()
+func (r *resourceAdapter) Data() interface{} {
+	r.init(false, false)
+	return r.target.Data()
 }
 
-// ResourceTransformation is the interface that a resource transformation step
-// needs to implement.
-type ResourceTransformation interface {
-	Key() ResourceTransformationKey
-	Transform(ctx *ResourceTransformationCtx) error
+func (r *resourceAdapter) Fill(spec string) (resource.Image, error) {
+	return r.getImageOps().Fill(spec)
 }
 
-// We will persist this information to disk.
-type transformedResourceMetadata struct {
-	Target     string                 `json:"Target"`
-	MediaTypeV string                 `json:"MediaType"`
-	MetaData   map[string]interface{} `json:"Data"`
+func (r *resourceAdapter) Fit(spec string) (resource.Image, error) {
+	return r.getImageOps().Fit(spec)
 }
 
-type transformedResource struct {
-	commonResource
+func (r *resourceAdapter) Height() int {
+	return r.getImageOps().Height()
+}
 
-	cache *ResourceCache
+func (r *resourceAdapter) Key() string {
+	r.init(false, false)
+	return r.target.(resource.Identifier).Key()
+}
 
-	// This is the filename inside resources/_gen/assets
-	sourceFilename string
+func (r *resourceAdapter) MediaType() media.Type {
+	r.init(false, false)
+	return r.target.MediaType()
+}
 
-	linker permalinker
+func (r *resourceAdapter) Name() string {
+	r.init(false, false)
+	return r.target.Name()
+}
 
-	// The transformation to apply.
-	transformation ResourceTransformation
+func (r *resourceAdapter) Params() map[string]interface{} {
+	r.init(false, false)
+	return r.target.Params()
+}
 
-	// We apply the tranformations lazily.
-	transformInit sync.Once
-	transformErr  error
+func (r *resourceAdapter) Permalink() string {
+	r.init(true, false)
+	return r.target.Permalink()
+}
 
-	// We delay publishing until either .RelPermalink or .Permalink
-	// is invoked.
-	publishInit sync.Once
-	published   bool
+func (r *resourceAdapter) Publish() error {
+	r.init(false, false)
 
-	// The transformed values
-	content     string
-	contentInit sync.Once
-	transformedResourceMetadata
+	return r.target.Publish()
+}
 
-	// The source
-	resource.Resource
+func (r *resourceAdapter) ReadSeekCloser() (hugio.ReadSeekCloser, error) {
+	r.init(false, false)
+	return r.target.ReadSeekCloser()
 }
 
-func (r *transformedResource) ReadSeekCloser() (hugio.ReadSeekCloser, error) {
-	if err := r.initContent(); err != nil {
-		return nil, err
-	}
-	return hugio.NewReadSeekerNoOpCloserFromString(r.content), nil
+func (r *resourceAdapter) RelPermalink() string {
+	r.init(true, false)
+	return r.target.RelPermalink()
 }
 
-func (r *transformedResource) transferTransformedValues(another *transformedResource) {
-	if another.content != "" {
-		r.contentInit.Do(func() {
-			r.content = another.content
-		})
-	}
-	r.transformedResourceMetadata = another.transformedResourceMetadata
+func (r *resourceAdapter) Resize(spec string) (resource.Image, error) {
+	return r.getImageOps().Resize(spec)
 }
 
-func (r *transformedResource) tryTransformedFileCache(key string) io.ReadCloser {
-	fi, f, meta, found := r.cache.getFromFile(key)
-	if !found {
-		return nil
-	}
-	r.transformedResourceMetadata = meta
-	r.sourceFilename = fi.Name
-
-	return f
+func (r *resourceAdapter) ResourceType() string {
+	r.init(false, false)
+	return r.target.ResourceType()
 }
 
-func (r *transformedResource) Content() (interface{}, error) {
-	if err := r.initTransform(true, false); err != nil {
-		return nil, err
-	}
-	if err := r.initContent(); err != nil {
-		return "", err
-	}
-	return r.content, nil
+func (r *resourceAdapter) String() string {
+	return r.Name()
 }
 
-func (r *transformedResource) Data() interface{} {
-	if err := r.initTransform(false, false); err != nil {
-		return noData
-	}
-	return r.MetaData
+func (r *resourceAdapter) Title() string {
+	r.init(false, false)
+	return r.target.Title()
 }
 
-func (r *transformedResource) MediaType() media.Type {
-	if err := r.initTransform(false, false); err != nil {
-		return media.Type{}
+func (r resourceAdapter) Transform(t ...ResourceTransformation) (ResourceTransformer, error) {
+	r.resourceTransformations = &resourceTransformations{
+		transformations: append(r.transformations, t...),
 	}
-	m, _ := r.cache.rs.MediaTypes.GetByType(r.MediaTypeV)
-	return m
-}
 
-func (r *transformedResource) Key() string {
-	if err := r.initTransform(false, false); err != nil {
-		return ""
+	r.resourceAdapterInner = &resourceAdapterInner{
+		spec:        r.spec,
+		publishOnce: &publishOnce{},
+		target:      r.target,
 	}
-	return r.linker.relPermalinkFor(r.Target)
+
+	return &r, nil
 }
 
-func (r *transformedResource) Permalink() string {
-	if err := r.initTransform(false, true); err != nil {
-		return ""
-	}
-	return r.linker.permalinkFor(r.Target)
+func (r *resourceAdapter) Width() int {
+	return r.getImageOps().Width()
 }
 
-func (r *transformedResource) RelPermalink() string {
-	if err := r.initTransform(false, true); err != nil {
-		return ""
+func (r *resourceAdapter) getImageOps() resource.ImageOps {
+	img, ok := r.target.(resource.ImageOps)
+	if !ok {
+		panic(fmt.Sprintf("%T is not an image", r.target))
 	}
-	return r.linker.relPermalinkFor(r.Target)
+	r.init(false, false)
+	return img
 }
 
-func (r *transformedResource) initContent() error {
-	var err error
-	r.contentInit.Do(func() {
-		var b []byte
-		_, b, err = r.cache.fileCache.GetBytes(r.sourceFilename)
-		if err != nil {
-			return
-		}
-		r.content = string(b)
-	})
-	return err
+func (r *resourceAdapter) getMetaAssigner() metaAssigner {
+	return r.target
 }
 
-func (r *transformedResource) openPublishFileForWriting(relTargetPath string) (io.WriteCloser, error) {
-	return helpers.OpenFilesForWriting(r.cache.rs.PublishFs, r.linker.relTargetPathsFor(relTargetPath)...)
+func (r *resourceAdapter) getSpec() *Spec {
+	return r.spec
 }
 
-func (r *transformedResource) transform(setContent, publish bool) (err error) {
+func (r *resourceAdapter) publish() {
+	if r.publishOnce == nil {
+		return
+	}
 
-	// This can be the last resource in a chain.
-	// Rewind and create a processing chain.
-	var chain []resource.Resource
-	current := r
-	for {
-		rr := current.Resource
-		chain = append(chain[:0], append([]resource.Resource{rr}, chain[0:]...)...)
-		if tr, ok := rr.(*transformedResource); ok {
-			current = tr
-		} else {
-			break
+	r.publisherInit.Do(func() {
+		r.publisherErr = r.target.Publish()
+
+		if r.publisherErr != nil {
+			r.spec.Logger.ERROR.Printf("Failed to publish Resource: %s", r.publisherErr)
 		}
-	}
+	})
 
-	// Append the current transformer at the end
-	chain = append(chain, r)
+}
 
-	first := chain[0]
+func (r *resourceAdapter) transform(publish, setContent bool) error {
+	cache := r.spec.ResourceCache
 
 	// Files with a suffix will be stored in cache (both on disk and in memory)
-	// partitioned by their suffix. There will be other files below /other.
-	// This partition is also how we determine what to delete on server reloads.
-	var key, base string
-	for _, element := range chain {
-		switch v := element.(type) {
-		case *transformedResource:
-			key = key + "_" + v.transformation.Key().key()
-		case permalinker:
-			r.linker = v
-			p := v.TargetPath()
-			if p == "" {
-				panic("target path needed for key creation")
-			}
-			base = ResourceCacheKey(p)
-		default:
-			return fmt.Errorf("transformation not supported for type %T", element)
-		}
+	// partitioned by their suffix.
+	var key string
+	for _, tr := range r.transformations {
+		key = key + "_" + tr.Key().Value()
 	}
 
-	key = r.cache.cleanKey(base) + "_" + helpers.MD5String(key)
+	base := ResourceCacheKey(r.target.TargetPath())
 
-	cached, found := r.cache.get(key)
+	key = cache.cleanKey(base) + "_" + helpers.MD5String(key)
+
+	cached, found := cache.get(key)
+
 	if found {
-		r.transferTransformedValues(cached.(*transformedResource))
-		return
+		r.resourceAdapterInner = cached.(*resourceAdapterInner)
+		return nil
 	}
 
 	// Acquire a write lock for the named transformation.
-	r.cache.nlocker.Lock(key)
+	cache.nlocker.Lock(key)
 	// Check the cache again.
-	cached, found = r.cache.get(key)
+	cached, found = cache.get(key)
 	if found {
-		r.transferTransformedValues(cached.(*transformedResource))
-		r.cache.nlocker.Unlock(key)
-		return
+		r.resourceAdapterInner = cached.(*resourceAdapterInner)
+		cache.nlocker.Unlock(key)
+		return nil
 	}
 
-	defer r.cache.nlocker.Unlock(key)
-	defer r.cache.set(key, r)
+	defer cache.nlocker.Unlock(key)
+	defer cache.set(key, r.resourceAdapterInner)
 
 	b1 := bp.GetBuffer()
 	b2 := bp.GetBuffer()
@@ -363,68 +325,77 @@
 	defer bp.PutBuffer(b2)
 
 	tctx := &ResourceTransformationCtx{
-		Data:                  r.transformedResourceMetadata.MetaData,
-		OpenResourcePublisher: r.openPublishFileForWriting,
+		Data:                  make(map[string]interface{}),
+		OpenResourcePublisher: r.target.openPublishFileForWriting,
 	}
 
-	tctx.InMediaType = first.MediaType()
-	tctx.OutMediaType = first.MediaType()
+	tctx.InMediaType = r.target.MediaType()
+	tctx.OutMediaType = r.target.MediaType()
 
-	contentrc, err := contentReadSeekerCloser(first)
+	startCtx := *tctx
+	updates := &transformationUpdate{startCtx: startCtx}
+
+	var contentrc hugio.ReadSeekCloser
+
+	contentrc, err := contentReadSeekerCloser(r.target)
 	if err != nil {
 		return err
 	}
+
 	defer contentrc.Close()
 
 	tctx.From = contentrc
 	tctx.To = b1
 
-	if r.linker != nil {
-		tctx.InPath = r.linker.TargetPath()
-		tctx.SourcePath = tctx.InPath
-	}
+	tctx.InPath = r.target.TargetPath()
+	tctx.SourcePath = tctx.InPath
 
 	counter := 0
+	writeToFileCache := false
 
 	var transformedContentr io.Reader
 
-	for _, element := range chain {
-		tr, ok := element.(*transformedResource)
-		if !ok {
-			continue
-		}
-		counter++
-		if counter != 1 {
+	for i, tr := range r.transformations {
+		if i != 0 {
 			tctx.InMediaType = tctx.OutMediaType
 		}
-		if counter%2 == 0 {
-			tctx.From = b1
-			b2.Reset()
-			tctx.To = b2
-		} else {
-			if counter != 1 {
-				// The first reader is the file.
-				tctx.From = b2
+
+		if !writeToFileCache {
+			writeToFileCache = transformationsToCacheOnDisk[tr.Key().Name]
+		}
+
+		if i > 0 {
+			hasWrites := tctx.To.(*bytes.Buffer).Len() > 0
+			if hasWrites {
+				counter++
+				// Switch the buffers
+				if counter%2 == 0 {
+					tctx.From = b2
+					b1.Reset()
+					tctx.To = b1
+				} else {
+					tctx.From = b1
+					b2.Reset()
+					tctx.To = b2
+				}
 			}
-			b1.Reset()
-			tctx.To = b1
 		}
 
-		if err := tr.transformation.Transform(tctx); err != nil {
-
-			if err == herrors.ErrFeatureNotAvailable {
+		if err = tr.Transform(tctx); err != nil {
+			if writeToFileCache && err == herrors.ErrFeatureNotAvailable {
 				// This transformation is not available in this
 				// Hugo installation (scss not compiled in, PostCSS not available etc.)
 				// If a prepared bundle for this transformation chain is available, use that.
-				f := r.tryTransformedFileCache(key)
+				f := r.target.tryTransformedFileCache(key, updates)
 				if f == nil {
 					errMsg := err.Error()
-					if tr.transformation.Key().name == "postcss" {
+					if tr.Key().Name == "postcss" {
 						errMsg = "PostCSS not found; install with \"npm install postcss-cli\". See https://gohugo.io/hugo-pipes/postcss/"
 					}
-					return fmt.Errorf("%s: failed to transform %q (%s): %s", strings.ToUpper(tr.transformation.Key().name), tctx.InPath, tctx.InMediaType.Type(), errMsg)
+					return fmt.Errorf("%s: failed to transform %q (%s): %s", strings.ToUpper(tr.Key().Name), tctx.InPath, tctx.InMediaType.Type(), errMsg)
 				}
 				transformedContentr = f
+				updates.sourceFs = cache.fileCache.Fs
 				defer f.Close()
 
 				// The reader above is all we need.
@@ -442,34 +413,35 @@
 	}
 
 	if transformedContentr == nil {
-		r.Target = tctx.InPath
-		r.MediaTypeV = tctx.OutMediaType.Type()
+		updates.updateFromCtx(tctx)
 	}
 
 	var publishwriters []io.WriteCloser
 
 	if publish {
-		publicw, err := r.openPublishFileForWriting(r.Target)
+		publicw, err := r.target.openPublishFileForWriting(updates.targetPath)
 		if err != nil {
-			r.transformErr = err
 			return err
 		}
-		defer publicw.Close()
-
 		publishwriters = append(publishwriters, publicw)
 	}
 
 	if transformedContentr == nil {
-		// Also write it to the cache
-		fi, metaw, err := r.cache.writeMeta(key, r.transformedResourceMetadata)
-		if err != nil {
-			return err
+		if writeToFileCache {
+			// Also write it to the cache
+			fi, metaw, err := cache.writeMeta(key, updates.toTransformedResourceMetadata())
+			if err != nil {
+				return err
+			}
+			updates.sourceFilename = &fi.Name
+			updates.sourceFs = cache.fileCache.Fs
+			publishwriters = append(publishwriters, metaw)
 		}
-		r.sourceFilename = fi.Name
 
-		publishwriters = append(publishwriters, metaw)
-
-		if counter > 0 {
+		// Any transofrmations reading from From must also write to To.
+		// This means that if the target buffer is empty, we can just reuse
+		// the original reader.
+		if b, ok := tctx.To.(*bytes.Buffer); ok && b.Len() > 0 {
 			transformedContentr = tctx.To.(*bytes.Buffer)
 		} else {
 			transformedContentr = contentrc
@@ -479,6 +451,8 @@
 	// Also write it to memory
 	var contentmemw *bytes.Buffer
 
+	setContent = setContent || !writeToFileCache
+
 	if setContent {
 		contentmemw = bp.GetBuffer()
 		defer bp.PutBuffer(contentmemw)
@@ -486,65 +460,111 @@
 	}
 
 	publishw := hugio.NewMultiWriteCloser(publishwriters...)
-	_, r.transformErr = io.Copy(publishw, transformedContentr)
+	_, err = io.Copy(publishw, transformedContentr)
+	if err != nil {
+		return err
+	}
 	publishw.Close()
 
 	if setContent {
-		r.contentInit.Do(func() {
-			r.content = contentmemw.String()
-		})
+		s := contentmemw.String()
+		updates.content = &s
 	}
 
+	newTarget, err := r.target.cloneWithUpdates(updates)
+	if err != nil {
+		return err
+	}
+	r.target = newTarget
+
 	return nil
 }
 
-func (r *transformedResource) initTransform(setContent, publish bool) error {
-	r.transformInit.Do(func() {
-		r.published = publish
-		if err := r.transform(setContent, publish); err != nil {
-			r.transformErr = err
-			r.cache.rs.Logger.ERROR.Println("error: failed to transform resource:", err)
+func (r *resourceAdapter) init(publish, setContent bool) {
+	r.initTransform(publish, setContent)
+}
+
+func (r *resourceAdapter) initTransform(publish, setContent bool) {
+	r.transformationsInit.Do(func() {
+		if len(r.transformations) == 0 {
+			// Nothing to do.
+			return
 		}
 
+		if publish {
+			// The transformation will write the content directly to
+			// the destination.
+			r.publishOnce = nil
+		}
+
+		r.transformationsErr = r.transform(publish, setContent)
+		if r.transformationsErr != nil {
+			r.spec.Logger.ERROR.Printf("Transformation failed: %s", r.transformationsErr)
+		}
 	})
 
-	if !publish {
-		return r.transformErr
+	if publish && r.publishOnce != nil {
+		r.publish()
 	}
+}
 
-	r.publishInit.Do(func() {
-		if r.published {
-			return
-		}
+type resourceAdapterInner struct {
+	target transformableResource
 
-		r.published = true
+	spec *Spec
 
-		// Copy the file from cache to /public
-		_, src, err := r.cache.fileCache.Get(r.sourceFilename)
-		if src == nil {
-			panic(fmt.Sprintf("[BUG] resource cache file not found: %q", r.sourceFilename))
-		}
+	// Handles publishing (to /public) if needed.
+	*publishOnce
+}
 
-		if err == nil {
-			defer src.Close()
+type resourceTransformations struct {
+	transformationsInit sync.Once
+	transformationsErr  error
+	transformations     []ResourceTransformation
+}
 
-			var dst io.WriteCloser
-			dst, err = r.openPublishFileForWriting(r.Target)
-			if err == nil {
-				defer dst.Close()
-				io.Copy(dst, src)
-			}
-		}
+type transformableResource interface {
+	baseResourceInternal
 
-		if err != nil {
-			r.transformErr = err
-			r.cache.rs.Logger.ERROR.Println("error: failed to publish resource:", err)
-			return
-		}
+	resource.ContentProvider
+	resource.Resource
+}
 
-	})
+type transformationUpdate struct {
+	content        *string
+	sourceFilename *string
+	sourceFs       afero.Fs
+	targetPath     string
+	mediaType      media.Type
+	data           map[string]interface{}
 
-	return r.transformErr
+	startCtx ResourceTransformationCtx
+}
+
+func (u *transformationUpdate) isContenChanged() bool {
+	return u.content != nil || u.sourceFilename != nil
+}
+
+func (u *transformationUpdate) toTransformedResourceMetadata() transformedResourceMetadata {
+	return transformedResourceMetadata{
+		MediaTypeV: u.mediaType.Type(),
+		Target:     u.targetPath,
+		MetaData:   u.data,
+	}
+}
+
+func (u *transformationUpdate) updateFromCtx(ctx *ResourceTransformationCtx) {
+	u.targetPath = ctx.OutPath
+	u.mediaType = ctx.OutMediaType
+	u.data = ctx.Data
+	u.targetPath = ctx.InPath
+}
+
+// We will persist this information to disk.
+type transformedResourceMetadata struct {
+	Target     string                 `json:"Target"`
+	MediaTypeV string                 `json:"MediaType"`
+	MetaData   map[string]interface{} `json:"Data"`
 }
 
 // contentReadSeekerCloser returns a ReadSeekerCloser if possible for a given Resource.
--- a/resources/transform_test.go
+++ b/resources/transform_test.go
@@ -14,23 +14,427 @@
 package resources
 
 import (
+	"encoding/base64"
+	"fmt"
+	"io"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"sync"
 	"testing"
 
+	"github.com/gohugoio/hugo/htesting"
+
+	"github.com/gohugoio/hugo/common/herrors"
+	"github.com/gohugoio/hugo/hugofs"
+
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/resources/internal"
+
+	"github.com/gohugoio/hugo/helpers"
+
+	"github.com/gohugoio/hugo/resources/resource"
+	"github.com/spf13/afero"
+
 	qt "github.com/frankban/quicktest"
 )
 
-type testStruct struct {
-	Name string
-	V1   int64
-	V2   int32
-	V3   int
-	V4   uint64
-}
+const gopher = `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`
 
-func TestResourceTransformationKey(t *testing.T) {
-	// We really need this key to be portable across OSes.
-	key := NewResourceTransformationKey("testing",
-		testStruct{Name: "test", V1: int64(10), V2: int32(20), V3: 30, V4: uint64(40)})
+func gopherPNG() io.Reader { return base64.NewDecoder(base64.StdEncoding, strings.NewReader(gopher)) }
+
+func TestTransform(t *testing.T) {
 	c := qt.New(t)
-	c.Assert("testing_518996646957295636", qt.Equals, key.key())
+
+	createTransformer := func(spec *Spec, filename, content string) Transformer {
+		filename = filepath.FromSlash(filename)
+		fs := spec.Fs.Source
+		afero.WriteFile(fs, filename, []byte(content), 0777)
+		r, _ := spec.New(ResourceSourceDescriptor{Fs: fs, SourceFilename: filename})
+		return r.(Transformer)
+	}
+
+	createContentReplacer := func(name, old, new string) ResourceTransformation {
+		return &testTransformation{
+			name: name,
+			transform: func(ctx *ResourceTransformationCtx) error {
+				in := helpers.ReaderToString(ctx.From)
+				in = strings.Replace(in, old, new, 1)
+				ctx.AddOutPathIdentifier("." + name)
+				fmt.Fprint(ctx.To, in)
+				return nil
+			},
+		}
+	}
+
+	// Verify that we publish the same file once only.
+	assertNoDuplicateWrites := func(c *qt.C, spec *Spec) {
+		c.Helper()
+		d := spec.Fs.Destination.(hugofs.DuplicatesReporter)
+		c.Assert(d.ReportDuplicates(), qt.Equals, "")
+	}
+
+	assertShouldExist := func(c *qt.C, spec *Spec, filename string, should bool) {
+		c.Helper()
+		exists, _ := helpers.Exists(filepath.FromSlash(filename), spec.Fs.Destination)
+		c.Assert(exists, qt.Equals, should)
+	}
+
+	c.Run("All values", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		transformation := &testTransformation{
+			name: "test",
+			transform: func(ctx *ResourceTransformationCtx) error {
+				// Content
+				in := helpers.ReaderToString(ctx.From)
+				in = strings.Replace(in, "blue", "green", 1)
+				fmt.Fprint(ctx.To, in)
+
+				// Media type
+				ctx.OutMediaType = media.CSVType
+
+				// Change target
+				ctx.ReplaceOutPathExtension(".csv")
+
+				// Add some data to context
+				ctx.Data["mydata"] = "Hugo Rocks!"
+
+				return nil
+			},
+		}
+
+		r := createTransformer(spec, "f1.txt", "color is blue")
+
+		tr, err := r.Transform(transformation)
+		c.Assert(err, qt.IsNil)
+		content, err := tr.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+
+		c.Assert(content, qt.Equals, "color is green")
+		c.Assert(tr.MediaType(), eq, media.CSVType)
+		c.Assert(tr.RelPermalink(), qt.Equals, "/f1.csv")
+		assertShouldExist(c, spec, "public/f1.csv", true)
+
+		data := tr.Data().(map[string]interface{})
+		c.Assert(data["mydata"], qt.Equals, "Hugo Rocks!")
+
+		assertNoDuplicateWrites(c, spec)
+	})
+
+	c.Run("Meta only", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		transformation := &testTransformation{
+			name: "test",
+			transform: func(ctx *ResourceTransformationCtx) error {
+				// Change media type only
+				ctx.OutMediaType = media.CSVType
+				ctx.ReplaceOutPathExtension(".csv")
+
+				return nil
+			},
+		}
+
+		r := createTransformer(spec, "f1.txt", "color is blue")
+
+		tr, err := r.Transform(transformation)
+		c.Assert(err, qt.IsNil)
+		content, err := tr.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+
+		c.Assert(content, qt.Equals, "color is blue")
+		c.Assert(tr.MediaType(), eq, media.CSVType)
+
+		// The transformed file should only be published if RelPermalink
+		// or Permalink is called.
+		n := htesting.RandIntn(3)
+		shouldExist := true
+		switch n {
+		case 0:
+			tr.RelPermalink()
+		case 1:
+			tr.Permalink()
+		default:
+			shouldExist = false
+		}
+
+		assertShouldExist(c, spec, "public/f1.csv", shouldExist)
+		assertNoDuplicateWrites(c, spec)
+	})
+
+	c.Run("Memory-cached transformation", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		// Two transformations with same id, different behaviour.
+		t1 := createContentReplacer("t1", "blue", "green")
+		t2 := createContentReplacer("t1", "color", "car")
+
+		for i, transformation := range []ResourceTransformation{t1, t2} {
+			r := createTransformer(spec, "f1.txt", "color is blue")
+			tr, _ := r.Transform(transformation)
+			content, err := tr.(resource.ContentProvider).Content()
+			c.Assert(err, qt.IsNil)
+			c.Assert(content, qt.Equals, "color is green", qt.Commentf("i=%d", i))
+
+			assertShouldExist(c, spec, "public/f1.t1.txt", false)
+		}
+
+		assertNoDuplicateWrites(c, spec)
+	})
+
+	c.Run("File-cached transformation", func(c *qt.C) {
+		c.Parallel()
+
+		fs := afero.NewMemMapFs()
+
+		for i := 0; i < 2; i++ {
+			spec := newTestResourceSpec(specDescriptor{c: c, fs: fs})
+
+			r := createTransformer(spec, "f1.txt", "color is blue")
+
+			var transformation ResourceTransformation
+
+			if i == 0 {
+				// There is currently a hardcoded list of transformations that we
+				// persist to disk (tocss, postcss).
+				transformation = &testTransformation{
+					name: "tocss",
+					transform: func(ctx *ResourceTransformationCtx) error {
+						in := helpers.ReaderToString(ctx.From)
+						in = strings.Replace(in, "blue", "green", 1)
+						ctx.AddOutPathIdentifier("." + "cached")
+						ctx.OutMediaType = media.CSVType
+						ctx.Data = map[string]interface{}{
+							"Hugo": "Rocks!",
+						}
+						fmt.Fprint(ctx.To, in)
+						return nil
+					},
+				}
+			} else {
+				// Force read from file cache.
+				transformation = &testTransformation{
+					name: "tocss",
+					transform: func(ctx *ResourceTransformationCtx) error {
+						return herrors.ErrFeatureNotAvailable
+					},
+				}
+			}
+
+			msg := qt.Commentf("i=%d", i)
+
+			tr, _ := r.Transform(transformation)
+			c.Assert(tr.RelPermalink(), qt.Equals, "/f1.cached.txt", msg)
+			content, err := tr.(resource.ContentProvider).Content()
+			c.Assert(err, qt.IsNil)
+			c.Assert(content, qt.Equals, "color is green", msg)
+			c.Assert(tr.MediaType(), eq, media.CSVType)
+			c.Assert(tr.Data(), qt.DeepEquals, map[string]interface{}{
+				"Hugo": "Rocks!",
+			})
+
+			assertNoDuplicateWrites(c, spec)
+			assertShouldExist(c, spec, "public/f1.cached.txt", true)
+
+		}
+	})
+
+	c.Run("Access RelPermalink first", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		t1 := createContentReplacer("t1", "blue", "green")
+
+		r := createTransformer(spec, "f1.txt", "color is blue")
+
+		tr, _ := r.Transform(t1)
+
+		relPermalink := tr.RelPermalink()
+
+		content, err := tr.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+
+		c.Assert(relPermalink, qt.Equals, "/f1.t1.txt")
+		c.Assert(content, qt.Equals, "color is green")
+		c.Assert(tr.MediaType(), eq, media.TextType)
+
+		assertNoDuplicateWrites(c, spec)
+		assertShouldExist(c, spec, "public/f1.t1.txt", true)
+	})
+
+	c.Run("Content two", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		t1 := createContentReplacer("t1", "blue", "green")
+		t2 := createContentReplacer("t1", "color", "car")
+
+		r := createTransformer(spec, "f1.txt", "color is blue")
+
+		tr, _ := r.Transform(t1, t2)
+		content, err := tr.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+
+		c.Assert(content, qt.Equals, "car is green")
+		c.Assert(tr.MediaType(), eq, media.TextType)
+
+		assertNoDuplicateWrites(c, spec)
+	})
+
+	c.Run("Content two chained", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		t1 := createContentReplacer("t1", "blue", "green")
+		t2 := createContentReplacer("t2", "color", "car")
+
+		r := createTransformer(spec, "f1.txt", "color is blue")
+
+		tr1, _ := r.Transform(t1)
+		tr2, _ := tr1.Transform(t2)
+
+		content1, err := tr1.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+		content2, err := tr2.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+
+		c.Assert(content1, qt.Equals, "color is green")
+		c.Assert(content2, qt.Equals, "car is green")
+
+		assertNoDuplicateWrites(c, spec)
+	})
+
+	c.Run("Content many", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		const count = 26 // A-Z
+
+		transformations := make([]ResourceTransformation, count)
+		for i := 0; i < count; i++ {
+			transformations[i] = createContentReplacer(fmt.Sprintf("t%d", i), fmt.Sprint(i), string(i+65))
+		}
+
+		var countstr strings.Builder
+		for i := 0; i < count; i++ {
+			countstr.WriteString(fmt.Sprint(i))
+		}
+
+		r := createTransformer(spec, "f1.txt", countstr.String())
+
+		tr, _ := r.Transform(transformations...)
+		content, err := tr.(resource.ContentProvider).Content()
+		c.Assert(err, qt.IsNil)
+
+		c.Assert(content, qt.Equals, "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
+
+		assertNoDuplicateWrites(c, spec)
+	})
+
+	c.Run("Image", func(c *qt.C) {
+		c.Parallel()
+
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		transformation := &testTransformation{
+			name: "test",
+			transform: func(ctx *ResourceTransformationCtx) error {
+				ctx.AddOutPathIdentifier(".changed")
+				return nil
+			},
+		}
+
+		r := createTransformer(spec, "gopher.png", helpers.ReaderToString(gopherPNG()))
+
+		tr, err := r.Transform(transformation)
+		c.Assert(err, qt.IsNil)
+		c.Assert(tr.MediaType(), eq, media.PNGType)
+
+		img, ok := tr.(resource.Image)
+		c.Assert(ok, qt.Equals, true)
+
+		c.Assert(img.Width(), qt.Equals, 75)
+		c.Assert(img.Height(), qt.Equals, 60)
+
+		// RelPermalink called.
+		resizedPublished1, err := img.Resize("40x40")
+		c.Assert(err, qt.IsNil)
+		c.Assert(resizedPublished1.Height(), qt.Equals, 40)
+		c.Assert(resizedPublished1.RelPermalink(), qt.Equals, "/gopher.changed_hu2e827f5a78333ebc04166dd643235dea_1462_40x40_resize_linear_2.png")
+		assertShouldExist(c, spec, "public/gopher.changed_hu2e827f5a78333ebc04166dd643235dea_1462_40x40_resize_linear_2.png", true)
+
+		// Permalink called.
+		resizedPublished2, err := img.Resize("30x30")
+		c.Assert(err, qt.IsNil)
+		c.Assert(resizedPublished2.Height(), qt.Equals, 30)
+		c.Assert(resizedPublished2.Permalink(), qt.Equals, "https://example.com/gopher.changed_hu2e827f5a78333ebc04166dd643235dea_1462_30x30_resize_linear_2.png")
+		assertShouldExist(c, spec, "public/gopher.changed_hu2e827f5a78333ebc04166dd643235dea_1462_30x30_resize_linear_2.png", true)
+
+		// Not published because none of RelPermalink or Permalink was called.
+		resizedNotPublished, err := img.Resize("50x50")
+		c.Assert(err, qt.IsNil)
+		c.Assert(resizedNotPublished.Height(), qt.Equals, 50)
+		//c.Assert(resized.RelPermalink(), qt.Equals, "/gopher.changed_hu2e827f5a78333ebc04166dd643235dea_1462_50x50_resize_linear_2.png")
+		assertShouldExist(c, spec, "public/gopher.changed_hu2e827f5a78333ebc04166dd643235dea_1462_50x50_resize_linear_2.png", false)
+
+		assertNoDuplicateWrites(c, spec)
+
+	})
+
+	c.Run("Concurrent", func(c *qt.C) {
+		spec := newTestResourceSpec(specDescriptor{c: c})
+
+		transformers := make([]Transformer, 10)
+		transformations := make([]ResourceTransformation, 10)
+
+		for i := 0; i < 10; i++ {
+			transformers[i] = createTransformer(spec, fmt.Sprintf("f%d.txt", i), fmt.Sprintf("color is %d", i))
+			transformations[i] = createContentReplacer("test", strconv.Itoa(i), "blue")
+		}
+
+		var wg sync.WaitGroup
+
+		for i := 0; i < 13; i++ {
+			wg.Add(1)
+			go func(i int) {
+				defer wg.Done()
+				for j := 0; j < 23; j++ {
+					id := (i + j) % 10
+					tr, err := transformers[id].Transform(transformations[id])
+					c.Assert(err, qt.IsNil)
+					content, err := tr.(resource.ContentProvider).Content()
+					c.Assert(err, qt.IsNil)
+					c.Assert(content, qt.Equals, "color is blue")
+					c.Assert(tr.RelPermalink(), qt.Equals, fmt.Sprintf("/f%d.test.txt", id))
+				}
+			}(i)
+		}
+		wg.Wait()
+
+		assertNoDuplicateWrites(c, spec)
+	})
+}
+
+type testTransformation struct {
+	name      string
+	transform func(ctx *ResourceTransformationCtx) error
+}
+
+func (t *testTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey(t.name)
+}
+
+func (t *testTransformation) Transform(ctx *ResourceTransformationCtx) error {
+	return t.transform(ctx)
 }
--- a/tpl/resources/resources.go
+++ b/tpl/resources/resources.go
@@ -22,7 +22,9 @@
 	_errors "github.com/pkg/errors"
 
 	"github.com/gohugoio/hugo/deps"
+	"github.com/gohugoio/hugo/resources"
 	"github.com/gohugoio/hugo/resources/resource"
+
 	"github.com/gohugoio/hugo/resources/resource_factories/bundler"
 	"github.com/gohugoio/hugo/resources/resource_factories/create"
 	"github.com/gohugoio/hugo/resources/resource_transformers/integrity"
@@ -174,7 +176,7 @@
 	}
 	data := args[1]
 
-	r, ok := args[2].(resource.Resource)
+	r, ok := args[2].(resources.ResourceTransformer)
 	if !ok {
 		return nil, fmt.Errorf("type %T not supported in Resource transformations", args[2])
 	}
@@ -201,9 +203,9 @@
 		}
 	}
 
-	r, ok := args[resIdx].(resource.Resource)
+	r, ok := args[resIdx].(resources.ResourceTransformer)
 	if !ok {
-		return nil, fmt.Errorf("%T is not a Resource", args[resIdx])
+		return nil, fmt.Errorf("%T can not be transformed", args[resIdx])
 	}
 
 	return ns.integrityClient.Fingerprint(r, algo)
@@ -211,7 +213,7 @@
 
 // Minify minifies the given Resource using the MediaType to pick the correct
 // minifier.
-func (ns *Namespace) Minify(r resource.Resource) (resource.Resource, error) {
+func (ns *Namespace) Minify(r resources.ResourceTransformer) (resource.Resource, error) {
 	return ns.minifyClient.Minify(r)
 }
 
@@ -219,7 +221,7 @@
 // object or a target path (string) as first argument.
 func (ns *Namespace) ToCSS(args ...interface{}) (resource.Resource, error) {
 	var (
-		r          resource.Resource
+		r          resources.ResourceTransformer
 		m          map[string]interface{}
 		targetPath string
 		err        error
@@ -266,7 +268,7 @@
 }
 
 // We allow string or a map as the first argument in some cases.
-func (ns *Namespace) resolveIfFirstArgIsString(args []interface{}) (resource.Resource, string, bool) {
+func (ns *Namespace) resolveIfFirstArgIsString(args []interface{}) (resources.ResourceTransformer, string, bool) {
 	if len(args) != 2 {
 		return nil, "", false
 	}
@@ -275,19 +277,19 @@
 	if !ok1 {
 		return nil, "", false
 	}
-	v2, ok2 := args[1].(resource.Resource)
+	v2, ok2 := args[1].(resources.ResourceTransformer)
 
 	return v2, v1, ok2
 }
 
 // This roundabout way of doing it is needed to get both pipeline behaviour and options as arguments.
-func (ns *Namespace) resolveArgs(args []interface{}) (resource.Resource, map[string]interface{}, error) {
+func (ns *Namespace) resolveArgs(args []interface{}) (resources.ResourceTransformer, map[string]interface{}, error) {
 	if len(args) == 0 {
 		return nil, nil, errors.New("no Resource provided in transformation")
 	}
 
 	if len(args) == 1 {
-		r, ok := args[0].(resource.Resource)
+		r, ok := args[0].(resources.ResourceTransformer)
 		if !ok {
 			return nil, nil, fmt.Errorf("type %T not supported in Resource transformations", args[0])
 		}
@@ -294,7 +296,7 @@
 		return r, nil, nil
 	}
 
-	r, ok := args[1].(resource.Resource)
+	r, ok := args[1].(resources.ResourceTransformer)
 	if !ok {
 		return nil, nil, fmt.Errorf("type %T not supported in Resource transformations", args[0])
 	}