Simplistic grayscale assignment for machine generated, color images
ppmdist [-intensity|-frequency] [ppmfile]
Reads a portable pixmap as input, performs a simplistic grayscale assignment intended for use with grayscale or bitmap printers.
Often conversion from ppm to pgm will yield an image with contrast too low for good printer output. The program maximizes contrast between the gray levels output.
A ppm input of n colors is read, and a pgm of n gray levels is written. The gray levels take on the values 0..n-1, while maxval takes on n-1.
The mapping from color to stepped grayscale can be performed in order of input pixel intensity, or input pixel frequency (number of repetitions).
-frequency
Sort input colors by the number of times a color appears in the input, before mapping to evenly distributed graylevels of output. -intensity Sort input colors by their grayscale intensity, before mapping to evenly distributed graylevels of output. This is the default.
Helpful only for images with a very small number of colors. Perhaps should have been an option to ppmtopgm(1).
Copyright (C) 1993 by Dan Stromberg.