ppmhist [-hexcolor | -float | -colorname | -map] [-nomap] [-noheader]
This program is part of Netpbm.
ppmhistreads a PPM image as input and generates a histogram of the
colors in the image, i.e. a list of all the colors and how many pixels
of each color are in the image.
The output is in one of two basic formats: a report for humans and a
PPM image for use by programs. The PPM image is actually quite read-
able by humans too.
You get this format by specifying (or defaulting to) the -nomap
The format is one line for each color in the input image.
By default, there are two lines of column header at the top. Use the
-noheader option to suppress those lines.
In each line, ppmhist identifies the color by red, green, and blue
components. By default, it lists each of these in decimal, using the
exact values that are in the PPM input. So if the image has a maxval
of 255, the numbers in the listing range from 0 to 255. With the
-hexcolor option, you can change these numbers to hexadecimal. With
the -float option, the numbers are fractional, adjusted to a maxval of
Each line lists the luminosity of the color. It is in decimal on the
same scale as the rgb values (see above).
Each line lists the number of pixels in the image that have the color.
This is in decimal.
You get this format with the -map option.
The output file is a genuine PPM image, but it is PPM Plain format and
contains comments so that it is not a lot different from the human
report described above.
As a PPM image, it can be useful as input to other programs that need
some kind of palette. The image is a single row with one column for
each distinct color in the image.
-float Print the color components and the luminosity as floating point
-map Generates a PPM file of the colormap for the image, with the
-nomap Generates the histogram for human reading. This is the
ppm, pgmhist, pnmcolormmap, pnmhistmap, ppmchange
Copyright (C) 1989 by Jef Poskanzer.
netpbm documentation 24 June 2005 Ppmhist User Manual(0)