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pgmnorm(1)					     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  con-
       trast by forcing the lightest pixels to white, the darkest
       pixels to  black,  and  linearly 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 pre-
       fix.

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			1

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