pnmhistmap

   Updated: 25 October 1993
   Table Of Contents

NAME

   pnmhistmap - draw a histogram for a PGM or PPM file

SYNOPSIS

   pnmhistmap [-black] [-white] [-max N] [-verbose] [pnmfile]

DESCRIPTION

   This program is part of Netpbm.

   pnmhistmap	reads  a PNM image as input and produces an image
showing a
   histogram of the color  (or	gray)  values  in  the	input.	A
graymap (PGM) input
   produces  a PBM output. A pixmap (PPM) input produces PPM out-
put 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.

   If the input is PBM, pnmhistmap produces an error message  and
no output
   image.

OPTIONS

   -black
	  Ignores the count of black pixels when scaling the his-
togram.
   -white
	  Ignores the count of white pixels when scaling the his-
togram.

   The -black and -white options, which can be used seperately or
together, are
   useful for images with a large percentage of pixels whose val-
ue 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 per-
centage of
	  single-color pixels which are not black or white.
   -verbose
	  Report  the  progress	 of  making  the  histogram,  in-
cluding the
	  largest-count value used to scale the output.

   You can abbreviate any option to its shortest unique prefix.

LIMITATIONS

   pnmhistmap assumes maxval is always 255. Images with a smaller
maxval will
   only use the lower-value side of the histogram. You can  over-
come this either
   by	piping	 the   input   through pnmdepth or by cutting and
scaling the
   lower-value	side  of the histogram. Neither is a particularly
elegant
   solution to the problem.

   The program does not allow you to specify the output size.

SEE ALSO

   pgmhist, ppmhist, pgm, ppm

AUTHOR

   Wilson H. Bent. Jr. (whb@usc.edu).
     _________________________________________________________________



Table Of Contents

     * NAME
     * SYNOPSIS
     * DESCRIPTION
     * OPTIONS
     * BUGS
     * SEE ALSO
     * AUTHOR

UNIX/Linux commands referenced on this page:

1. as
2. red
3. which
4. pnmdepth
5. pgmhist
6. ppmhist