redhat man page for pgmnorm

pgmnorm(1)						      General Commands Manual							pgmnorm(1)

NAME
       pgmnorm - normalize the contrast in a portable graymap

SYNOPSIS
       pgmnorm [-bpercent N | -bvalue N] [-wpercent N | -wvalue N] [pgmfile]

DESCRIPTION
       Reads  a portable graymap as input.  Normalizes the contrast by forcing the lightest pixels to white, the darkest pixels to black, and lin-
       early rescaling the ones in between; and produces a portable graymap as output.

OPTIONS
       By default, the darkest 2 percent of all pixels are mapped to black, and the lightest 1 percent are mapped  to  white.	You  can  override
       these  percentages  by using the -bpercent and -wpercent flags, or you can specify the exact pixel values to be mapped by using the -bvalue
       and -wvalue flags.  Appropriate numbers for the flags can be gotten from the pgmhist tool.  If you just want to enhance the contrast,  then
       choose  values  at  elbows in the histogram; e.g. if value 29 represents 3% of the image but value 30 represents 20%, choose 30 for bvalue.
       If you want to lighten the image, then set bvalue to 0 and just fiddle with wvalue; similarly, to darken the image, set	wvalue	to  maxval
       and play with bvalue.

       All flags can be abbreviated to their shortest unique prefix.

SEE ALSO
       pgmhist(1), ppmnorm(1), pgm(5)

AUTHOR
       Partially based on the fbnorm filter in Michael Mauldin's "Fuzzy Pixmap" package.

       Copyright (C) 1989 by Jef Poskanzer.

								 28 February 1989							pgmnorm(1)