harvey/sys/src/cmd/postscript/postmd

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.