NAME

       ppmhist - print a histogram of the colors in a PPM image

SYNOPSIS

       ppmhist [-map | -nomap] [-hexcolor | -float | -colorname] [-noheader] [-sort={frequency,rgb}] [-forensic]
       [ppmfile]

DESCRIPTION

       This program is part of Netpbm(1).

       ppmhist  reads  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.

   Output Format
       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 readable by humans too.

       Human Report

       You get this format by specifying (or defaulting to) the -nomap option.

       The format is one line for each color in the input image.

       By default, there are two lines of column header and a summary at the top.  Use the -noheader  option  to
       suppress those lines.

       The  summary  tells  you  whether  black  or  white are present and how many shades of gray and color are
       present.  The summary was new in Netpbm 10.82 (March 2018).

       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 1.

       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.

       PPM Output

       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.

       The function of PPM output is essentially the same as the output of pnmcolormap  all.   ppmhist  is  much
       older than pnmcolormap.

OPTIONS

       In  addition  to  the options common to all programs based on libnetpbm (most notably -quiet, see  Common
       Options ), ppmhist recognizes the following command line options:

       -sort={frequency,rgb}
              The -sort option determines the order in which the colors are listed in the output.  rgb means  to
              sort them first by the intensity of the red component of the color, then of the green, then of the
              blue,  with  the least intense first.  frequency means to list them in order of how many pixels in
              the input image have the color, with the most represented colors first.   Among  colors  with  the
              same frequency, the order is the same as with rgb.

              The default is frequency.

              Before Netpbm 10.88 (September 2019), with -sort=frequency, the order of colors that have the same
              frequency is arbitrary.

       -hexcolor
              Print the color components in hexadecimal.  See output format .

              You may not specify this option along with -float or map.

       -float Print  the  color components and the luminosity as floating point numbers in the range [0,1].  See
              output format .

              You may not specify this option along with -hexcolor or map.

              This option was added in Netpbm 10.19 (November 2003).

       -map   Generates a PPM file of the colormap for the image, with the color  histogram  as  comments.   See
              output format .

              You may not specify this option along with -float or hexcolor.

       -nomap Generates the histogram for human reading.  This is the default.

       -colorname
              Add  the  color  name  to the output.  This is the name from the system color dictionary .  If the
              exact color is not in the color dictionary, it is an asterisk followed by the name of the  closest
              color that is in the dictionary.  If you don't have a system color dictionary, the program fails.

              This option was added in Netpbm 10.10 (October 2002).

       -noheader
              Do not print the column headings.

       -forensic

              With this option, ppmhist works on images that contain invalid sample values.  Normally, like most
              Netpbm  programs,  ppmhist  fails if it encounters a sample value greater than the maxval that the
              image declares.  The presence of such a value means the image is invalid, so the  pixels  have  no
              meaning.   But  with  -forensic,  ppmhist produces a histogram of the actual sample values without
              regard to maxval.  It issues messages summarizing the invalid pixels if there are any.

              One use for this is to diagnose the problem that caused the invalid Netpbm image to exist.

              There is a small exception to  the  ability  of  ppmhist  to  process  invalid  pixels  even  with
              -forensic:  it  can never process a sample value greater than 65535.  Note that in the rarely used
              Plain PPM format, it is possible for a number greater than that to appear  where  a  sample  value
              belongs.

              This  option  was new in Netpbm 10.66 (March 2014).  But Netpbm older than 10.66 does not properly
              reject invalid sample values, so the effect is very similar to -forensic.

SEE ALSO

       ppm(1), pgmhist(1), pnmcolormap(1), pnmhistmap(1), ppmchange(1)

AUTHOR

       Copyright (C) 1989 by Jef Poskanzer.

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master  documentation
       is at

              http://netpbm.sourceforge.net/doc/ppmhist.html

netpbm documentation                             24 August 2019                           Ppmhist User Manual(1)