1Pnmhistmap User Manual(0)                            Pnmhistmap User Manual(0)
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NAME

6       pnmhistmap - draw a histogram for a PGM or PPM file
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SYNOPSIS

10       pnmhistmap
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12       [-red] [-green] [-blue]
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14       [-black] [-white]
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16       [-max N]
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18       [-lval] [-rval]
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20       [-height] [-width]
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22       [-dots]
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24       [-verbose]
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26       [pnmfile]
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28       Minimum  unique abbreviation of option is acceptable.  You may use dou‐
29       ble hyphens instead of single hyphen to denote options.   You  may  use
30       white space in place of the equals sign to separate an option name from
31       its value.
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DESCRIPTION

35       This program is part of Netpbm(1).
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37       pnmhistmap reads a PNM image as input and produces an image  showing  a
38       histogram  of  the  color  (or  gray) values in the input.  A PGM input
39       results in a PBM output.  A PPM input results  in  a  PPM  output  with
40       three overlaid histograms: a red one for the red input, a green one for
41       the green input, and a blue one for the blue input.
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43       For example, from the following image produces the following histogram:
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45       image histogram from image
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47       If the input is PBM, pnmhistmap produces an error message and no output
48       image.
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OPTIONS

52       -red
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54       -green
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56       -blue  Include  the  indicated  color  component in the output.  If you
57              specify none of these, pnmhistmap include all three.
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59              These options are meaningless if the input is PGM.
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61              These options were new in Netpbm 10.26 (January  2005).   Before
62              that, pnmhistmap always included all three color components.
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65       -dots  Plot the histogram as dots.  By default, pnmhistmap plots bars.
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67              Example of dots:.B -dots example
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69              This  option  was  new  in  Netpbm 10.26 (January 2005).  Before
70              that, pnmhistmap always plotted bars.
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73       -lval minpixval
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75       -rval maxpixval
76              These options specify the range of intensity values to  include.
77              pnmhistmap  ignores  intensities less than minpixval and greater
78              than maxpixval.  So the left side of the  histogram  corresponds
79              to minpixval and the right side corresponds to maxpixval.
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81              By  default, pnmhistmap plots the entire possible range: zero to
82              the maxval.
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84              These options were new in Netpbm 10.26 (January  2005).   Before
85              that, pnmhistmap always plotted from zero to the maxval.
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88       -height
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90       -width These options specify the dimensions, in pixels of the histogram
91              image.
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93              The default height is 200 pixels.
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95              The default width is one pixel for each plotted intensity  value
96              (so it's controlled by the maxval of the image and the -lval and
97              -rval options).  The 'count buckets' in the histogram are always
98              one  pixel wide.  If you specify a width less than the number of
99              plotted intensity values, a  bucket  represents  more  than  one
100              intensity value.  If you specify a width greater that the number
101              of plotted intensity values, some  buckets  represent  no  color
102              (the count is zero).
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104              This  option  was  new  in  Netpbm 10.26 (January 2005).  Before
105              that, the dimensions were always what the default is today.
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108       -black Ignore the count of black pixels when scaling the histogram.
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111       -white Ignore the count of white pixels when scaling the histogram.
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113              The -black and -white options, which can be used  separately  or
114              together,  are useful for images with a large percentage of pix‐
115              els whose value is zero or 255, which can  cause  the  remaining
116              histogram data to become unreadbaly small.  Note that, for color
117              inputs, these options apply to all colors; if, for example,  the
118              input  has a large number of bright-red areas, you will probably
119              want to use the -white option.
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122       -max N Force the scaling of the histogram to use N as the largest-count
123              value.   This  is  useful  for inputs with a large percentage of
124              single-color pixels which are not black or white.
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127       -verbose
128              Report the progress  of  making  the  histogram,  including  the
129              largest-count value used to scale the output.
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LIMITATIONS

136       pnmhistmap  assumes maxval is always 255.  Images with a smaller maxval
137       will only use the lower-value side of the histogram.  You can  overcome
138       this  either  by  piping  the  input through pamdepth or by cutting and
139       scaling the lower-value side of the histogram.  Neither is  a  particu‐
140       larly elegant solution to the problem.
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SEE ALSO

144       pgmhist(1), ppmhist(1), pgm(1), ppm(1)
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AUTHOR

148       Wilson H. Bent. Jr. (whb@usc.edu).
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152netpbm documentation             13 July 2009        Pnmhistmap User Manual(0)