NAME

       pgmhist - print a histogram of the values in a PGM image

SYNOPSIS

       pgmhist

       [-median, -quartile, -decile]

       [-forensic]

       [-machine]

       [pgmfile]

DESCRIPTION

       This program is part of Netpbm(1).

       pgmhist reads a PGM image as input and prints a histogram of the gray values or other gray
       value distribution metrics.

       If you specify none of -median, -quartile, or -decile, pgmhist prints a complete histogram
       showing  how  many pixels of each possible gray value exist in the image.  Along with each
       gray value, it tells you how many pixels are at lest as black as it and how  many  are  at
       least as white.

       -median,  -quartile,  and  -decile  options  cause  pgmhist instead to print the indicated
       quantiles.  Each quantile is a gray value that actually appears in the image  (as  opposed
       to  fractional  values  that  are  sometimes used for quantiles).  The 3rd quartile is the
       least gray value for which at least 75% of the pixels are as dark or darker than it.   The
       4th quartile is the brightest gray value that appears in the image.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common Options ⟨index.html#commonoptions⟩ ), pgmhist  recognizes  the  following  command
       line options:

       You  may  specify  at  most  one  of -median, -quartile, and -decile.  If none of these is
       specified pgmhist prints a histogram of gray values.

       -median

              This option causes pgmhist to print the median gray value.

              This option was new in Netpbm 10.61 (December 2012).

       -quartile

              This option causes pgmhist to print the four quartile gray values.

              This option was new in Netpbm 10.61 (December 2012).

       -decile

              This option causes pgmhist to print the ten decile gray values.

              This option was new in Netpbm 10.61 (December 2012).

       -forensic

              With this option, pgmhist  works  on  images  that  contain  invalid  gray  values.
              Normally,  like  most  Netpbm programs, pgmhist fails if it encounters a gray 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,
              pgmhist produces a histogram of the actual gray 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 pgmhist to process invalid pixels even
              with -forensic: it can never process a gray value greater than 65535.  Note that in
              the rarely used Plain PGM format, it is possible for a number greater than that  to
              appear where a gray 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.

       -machine

              This option causes pgmhist to print the information in a way easily digestible by a
              machine as opposed to a human.

              For the quantiles, there is one line  per  quantile,  in  quantile  order,  and  it
              consists of the gray value of the quantile in decimal with no leading zeroes.

              For  the  full  histogram  output,  it consists of one line per possible gray value
              (whether that value appears in the image or not), in order of the gray values.  The
              line consists of two tokens separated by a space.  The first is the gray value; the
              second is the number of pixels in the image that have that gray  value.   Both  are
              decimal numbers without leading zeroes.

              This option was new in Netpbm 10.61 (December 2012).

SEE ALSO

       pnmnorm(1), ppmhist(1), pgm(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/pgmhist.html