Pgmhist User Manual(0)                                  Pgmhist User Manual(0)



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 more black and more white that it.

       -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
       You must specify exactly one of the ramp type options.


       -median

              This option causes pgmhist to print the median gray value.

              You may specify at most one of -median, -quartile, and -decile.

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


       -quartile

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

              You may specify at most one of -median, -quartile, and -decile.

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


       -decile

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

              You may specify at most one of -median, -quartile, and -decile.

              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(5) ,


AUTHOR
       Copyright (C) 1989 by Jef Poskanzer.

netpbm documentation             2 March 2014           Pgmhist User Manual(0)