Manual: pgmhist

Pgmhist User Manual(1)				   General Commands Manual			      Pgmhist User Manual(1)

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 met‐
       rics.

       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 quan‐
       tiles).	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  ),
       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 his‐
       togram 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	pro‐
	      grams, pgmhist fails if it encounters a gray value greater than the maxval that the image declares.  The pres‐
	      ence  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 in‐
	      valid 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

netpbm documentation				      18 December 2021				      Pgmhist User Manual(1)