PNMHISTMAP

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).