ref: 02d09919941c8f33f93f9e643a2aebb1fea14a91
dir: /sys/src/cmd/postscript/postmd/README/
A program that displays a matrix as a gray scale image on PostScript printers. May be useful if you have a large matrix and want a simple way to look for patterns. Expect a 600x600 matrix is an optimistic upper limit on a 300 dpi printers using 5 shades of gray and 8.5x11 inch paper. Matrix elements are a series of floating point numbers arranged in the input file in row major order. By default each matrix is assumed to be square and the number of rows (and columns) is set to the square root of the number of elements in the input file. White space, including newlines, is not used to determine the matrix dimensions. Each matrix element is mapped into an integer in the range 0 to 255 (254 by default) and PostScript's image operator maps that integer into a gray scale appropriate for the printer. The mapping from floating point matrix elements to integers is controlled by an interval list and grayscale map. The default interval list is "-1,0,1" which partitions the real line into 7 regions. The default grayscale map gets darker as the regions move from left to right along the real line. The -i option changes the interval list and the -g option modifies the grayscale mapping. Check the man page for more details.