1Pgmhist User Manual(0)                                  Pgmhist User Manual(0)
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NAME

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

10       pgmhist
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12       [-median, -quartile, -decile]
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14       [-forensic]
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16       [-machine]
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18       [pgmfile]
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DESCRIPTION

22       This program is part of Netpbm(1).
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24       pgmhist  reads  a PGM image as input and prints a histogram of the gray
25       values or other gray value distribution metrics.
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27       If you specify none of -median, -quartile, or -decile, pgmhist prints a
28       complete  histogram showing how many pixels of each possible gray value
29       exist in the image.  Along with each gray value, it tells you how  many
30       pixels are at lest as black as it and how many are at least as white.
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32       -median,  -quartile, and -decile options cause pgmhist instead to print
33       the indicated quantiles.  Each quantile is a gray value  that  actually
34       appears  in  the  image (as opposed to fractional values that are some‐
35       times used for quantiles).  The 3rd quartile is the  least  gray  value
36       for  which  at  least  75% of the pixels are as dark or darker than it.
37       The 4th quartile is the brightest gray value that appears in the image.
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OPTIONS

42       In addition to the options common to all programs  based  on  libnetpbm
43       (most notably -quiet, see
44        Common  Options  ⟨index.html#commonoptions⟩  ), pgmhist recognizes the
45       following command line options:
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47       You may specify at most one of -median,  -quartile,  and  -decile.   If
48       none of these is specified pgmhist prints a histogram of gray values.
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52       -median
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54              This option causes pgmhist to print the median gray value.
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56              This option was new in Netpbm 10.61 (December 2012).
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59       -quartile
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61              This  option causes pgmhist to print the four quartile gray val‐
62              ues.
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64              This option was new in Netpbm 10.61 (December 2012).
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67       -decile
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69              This option causes pgmhist to print the ten decile gray values.
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71              This option was new in Netpbm 10.61 (December 2012).
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74       -forensic
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76              With this option, pgmhist works on images that  contain  invalid
77              gray values.  Normally, like most Netpbm programs, pgmhist fails
78              if it encounters a gray value greater than the maxval  that  the
79              image declares.  The presence of such a value means the image is
80              invalid, so the pixels have no  meaning.   But  with  -forensic,
81              pgmhist  produces  a histogram of the actual gray values without
82              regard to maxval.  It issues messages  summarizing  the  invalid
83              pixels if there are any.
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85              One  use for this is to diagnose the problem that caused the in‐
86              valid Netpbm image to exist.
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88              There is a small exception to the ability of pgmhist to  process
89              invalid  pixels even with -forensic: it can never process a gray
90              value greater than 65535.  Note that in the  rarely  used  Plain
91              PGM format, it is possible for a number greater than that to ap‐
92              pear where a gray value belongs.
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94              This option was new in Netpbm 10.66 (March  2014).   But  Netpbm
95              older than 10.66 does not properly reject invalid sample values,
96              so the effect is very similar to -forensic.
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99       -machine
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101              This option causes pgmhist to print the  information  in  a  way
102              easily digestible by a machine as opposed to a human.
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104              For  the  quantiles, there is one line per quantile, in quantile
105              order, and it consists of the gray value of the quantile in dec‐
106              imal with no leading zeroes.
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108              For  the full histogram output, it consists of one line per pos‐
109              sible gray value (whether that value appears  in  the  image  or
110              not), in order of the gray values.  The line consists of two to‐
111              kens separated by a space.  The first is  the  gray  value;  the
112              second  is the number of pixels in the image that have that gray
113              value.  Both are decimal numbers without leading zeroes.
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115              This option was new in Netpbm 10.61 (December 2012).
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SEE ALSO

122       pnmnorm(1), ppmhist(1), pgm(1)
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AUTHOR

126       Copyright (C) 1989 by Jef Poskanzer.
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DOCUMENT SOURCE

129       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
130       source.  The master documentation is at
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132              http://netpbm.sourceforge.net/doc/pgmhist.html
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134netpbm documentation           18 December 2021         Pgmhist User Manual(0)
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