pnmhistmap(1) - man - phpMan

pnmhistmap(1)                          General Commands Manual                         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 pix‐
       els 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  im‐
       ages  with  a  large percentage of pixels whose value is zero or 255, which can cause the re‐
       maining histogram data to become unreadbaly small.  Note that, for pixmap inputs,  these  op‐
       tions 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  use‐
              ful  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 particu‐
       larly 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 AT usc.edu).



                                           25 October 1993                             pnmhistmap(1)