pnmhistmap(1)                                       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 out-
       put.  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  seper-
       ately or together, are useful for images with a large per-
       centage 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 num-
       ber 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 pre-
       fix.

BUGS
       Assumes  maxval is always 255.  Images with a smaller max-
       val 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                        1