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Pnmhistmap User Manual(0)                            Pnmhistmap User Manual(0)



NAME
       pnmhistmap - draw a histogram for a PGM or PPM file


SYNOPSIS
       pnmhistmap

       [-red] [-green] [-blue]

       [-black] [-white]

       [-max N]

       [-lval] [-rval]

       [-height] [-width]

       [-dots]

       [-verbose]

       [pnmfile]

       Minimum  unique  abbreviation  of option is acceptable.  You may use double hyphens instead of single hyphen to
       denote options.  You may use white space in place of the equals sign to separate an option name from its value.


DESCRIPTION
       This program is part of Netpbm(1).

       pnmhistmap  reads  a PNM image as input and produces an image showing a histogram of the color (or gray) values
       in the input.  A PGM input results in a PBM output.  A PPM input results in a PPM output  with  three  overlaid
       histograms: a red one for the red input, a green one for the green input, and a blue one for the blue input.

       For example, from the following image produces the following histogram:

       image histogram from image

       If the input is PBM, pnmhistmap produces an error message and no output image.


OPTIONS
       -red

       -green

       -blue  Include  the  indicated color component in the output.  If you specify none of these, pnmhistmap include
              all three.

              These options are meaningless if the input is PGM.

              These options were new in Netpbm 10.26 (January 2005).  Before  that,  pnmhistmap  always  included  all
              three color components.


       -dots  Plot the histogram as dots.  By default, pnmhistmap plots bars.

              Example of dots:.B -dots example

              This option was new in Netpbm 10.26 (January 2005).  Before that, pnmhistmap always plotted bars.


       -lval minpixval

       -rval maxpixval
              These  options  specify  the  range of intensity values to include.  pnmhistmap ignores intensities less
              than minpixval and greater than maxpixval.  So the left side of the histogram corresponds  to  minpixval
              and the right side corresponds to maxpixval.

              By default, pnmhistmap plots the entire possible range: zero to the maxval.

              These options were new in Netpbm 10.26 (January 2005).  Before that, pnmhistmap always plotted from zero
              to the maxval.


       -height

       -width These options specify the dimensions, in pixels of the histogram image.

              The default height is 200 pixels.

              The default width is one pixel for each plotted intensity value (so it's controlled by the maxval of the
              image and the -lval and -rval options).  The 'count buckets' in the histogram are always one pixel wide.
              If you specify a width less than the number of plotted intensity values, a bucket represents  more  than
              one  intensity  value.  If you specify a width greater that the number of plotted intensity values, some
              buckets represent no color (the count is zero).

              This option was new in Netpbm 10.26 (January 2005).  Before that, the dimensions were  always  what  the
              default is today.


       -black Ignore the count of black pixels when scaling the histogram.


       -white Ignore the count of white pixels when scaling the histogram.

              The  -black  and  -white options, which can be used separately or together, are useful for images with a
              large percentage of pixels whose value is zero or 255, which can cause the remaining histogram  data  to
              become  unreadbaly small.  Note that, for color inputs, these options apply to all colors; if, for exam-
              ple, the input has a large number of bright-red areas, you will probably want to use the -white  option.


       -max N Force  the scaling of the histogram to use N as the largest-count value.  This is useful for inputs with
              a large percentage of single-color pixels which are not black or white.


       -verbose
              Report the progress of making the histogram, including the largest-count value used to scale the output.





LIMITATIONS
       pnmhistmap  assumes  maxval  is always 255.  Images with a smaller maxval will only use the lower-value side of
       the histogram.  You can overcome this either by piping the input through pamdepth or by cutting and scaling the
       lower-value side of the histogram.  Neither is a particularly elegant solution to the problem.


SEE ALSO
       pgmhist(1), ppmhist(1), pgm(1), ppm(1)


AUTHOR
       Wilson H. Bent. Jr. (whbATusc.edu).



netpbm documentation             13 July 2009        Pnmhistmap User Manual(0)