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)