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       pnmhistmap - draw a histogram for a PGM or PPM file


       pnmhistmap [-black] [-white] [-max N] [-verbose] [pnmfile]


       Reads  a  portable  anymap as input, although bitmap (PBM) input produces an error message
       and no image.  Produces an image showing a histogram of the color (or gray) values in  the
       input.   A  graymap  (PGM)  input produces a bitmap output.  A pixmap (PPM) input produces
       pixmap 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.  The output is fixed in size: 256
       pixels wide by 200 pixels high.


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

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

       The -black and -white options, which can be used seperately 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 pixmap inputs,  these
       options  apply  to all colors; if, for example, 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.

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

       All flags can be abbreviated to their shortest unique prefix.


       Assumes  maxval is always 255.  Images with a smaller maxval will only use the lower-value
       side of the histogram.  This can be overcome either by piping the input through  "pnmdepth
       255"  or  by  cutting  and  scaling  the  lower-value side of the histogram.  Neither is a
       particularly elegant solution.

       Should allow the output size to be specified.


       pgmhist(1), ppmhist(1), pgm(5), ppm(5)


       Wilson H. Bent. Jr. (

                                         25 October 1993                            pnmhistmap(1)