man > ppmhist(1)

Ppmhist User Manual(1)                 General Commands Manual                Ppmhist User Manual(1)

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


SYNOPSIS
       ppmhist [-hexcolor | -float | -colorname | -map] [-nomap] [-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 rep‐
              resented 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 com‐
              ments.  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 the closest color that is  in
              the dictionary and is preceded by a '*'.  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.  Nor‐
              mally, 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 pro‐
              duces 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 ap‐
              pear 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)