pnmhistmap(1)

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)

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Free and Open Source Software