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NAME

       pnmhistmap - draw a histogram for a PGM or PPM file

SYNOPSIS

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

DESCRIPTION

       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.

OPTIONS

       -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.

       -verbose
              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.

BUGS

       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.

SEE ALSO

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

AUTHOR

       Wilson H. Bent. Jr. (whb@usc.edu).

                                25 October 1993                  pnmhistmap(1)