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       [-black]
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14       [-white]
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16       [-max N]
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18       [-verbose]
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20       [pnmfile]
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DESCRIPTION

24       This program is part of Netpbm(1).
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26       pnmhistmap  reads  a PNM image as input and produces an image showing a
27       histogram of the color (or gray) values in  the  input.   A  PGM  input
28       results  in  a  PBM  output.   A PPM input results in a PPM output with
29       three overlaid histograms: a red one for the red input, a green one for
30       the green input, and a blue one for the blue input.
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32       For example, from the following image produces the following histogram:
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34       image histogram from image
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36       If the input is PBM, pnmhistmap produces an error message and no output
37       image.
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OPTIONS

41       Minimum unique abbreviation of option is acceptable.  You may use  dou‐
42       ble  hyphens  instead  of single hyphen to denote options.  You may use
43       white space in place of the equals sign to separate an option name from
44       its value.
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49       -red
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51       -green
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53       -blue  Include  the  indicated  color  component in the output.  If you
54              specify none of these, pnmhistmap include all three.
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56              These options are meaningless if the input is PGM.
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58              These options were new in Netpbm 10.26 (January  2005).   Before
59              that, pnmhistmap always included all three color components.
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62       -dots  Plot the histogram as dots.  By default, pnmhistmap plots bars.
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64              Example of dots:.B -dots example
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66              This  option  was  new  in  Netpbm 10.26 (January 2005).  Before
67              that, pnmhistmap always plotted bars.
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70       -lval minpixval
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72       -rval maxpixval
73              These options specify the range of intensity values to  include.
74              pnmhistmap  ignores  intensities less than minpixval and greater
75              than maxpixval.  So the left side of the  histogram  corresponds
76              to minpixval and the right side corresponds to maxpixval.
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78              By  default, pnmhistmap plots the entire possible range: zero to
79              the maxval.
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81              These options were new in Netpbm 10.26 (January  2005).   Before
82              that, pnmhistmap always plotted from zero to the maxval.
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85       -height
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87       -width These options specify the dimensions, in pixels of the histogram
88              image.
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90              The default height is 200 pixels.
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92              The default width is one pixel for each plotted intensity  value
93              (so it's controlled by the maxval of the image and the -lval and
94              -rval options).  The 'count buckets' in the histogram are always
95              one  pixel wide.  If you specify a width less than the number of
96              plotted intensity values, a  bucket  represents  more  than  one
97              intensity value.  If you specify a width greater that the number
98              of plotted intensity values, some  buckets  represent  no  color
99              (the count is zero).
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101              This  option  was  new  in  Netpbm 10.26 (January 2005).  Before
102              that, the dimensions were always what the default is today.
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109       -black Ignore the count of black pixels when scaling the histogram.
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112       -white Ignore the count of white pixels when scaling the histogram.
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116       The -black  and  -white  options,  which  can  be  used  separately  or
117       together, are useful for images with a large percentage of pixels whose
118       value is zero or 255, which can cause the remaining histogram  data  to
119       become  unreadbaly  small.   Note that, for color inputs, these options
120       apply to all colors; if, for example, the input has a large  number  of
121       bright-red areas, you will probably want to use the -white option.
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125       -max N Force the scaling of the histogram to use N as the largest-count
126              value.  This is useful for inputs with  a  large  percentage  of
127              single-color pixels which are not black or white.
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130       -verbose
131              Report  the  progress  of  making  the  histogram, including the
132              largest-count value used to scale the output.
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LIMITATIONS

139       pnmhistmap assumes maxval is always 255.  Images with a smaller  maxval
140       will  only use the lower-value side of the histogram.  You can overcome
141       this either by piping the input through  pamdepth  or  by  cutting  and
142       scaling  the  lower-value side of the histogram.  Neither is a particu‐
143       larly elegant solution to the problem.
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145       The program does not allow you to specify the output size.
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SEE ALSO

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

153       Wilson H. Bent. Jr. (whb@usc.edu).
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157netpbm documentation            25 October 1993      Pnmhistmap User Manual(0)