ppmdist – simplistic grayscale assignment for machine generated, color
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 repeti‐
-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 dis‐
tributed 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.
Copyright (C) 1993 by Dan Stromberg.
22 July 1992 ppmdist