pgmnorm man page on DigitalUNIX

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pgmnorm(1)							    pgmnorm(1)

       pgmnorm - normalize the contrast in a portable graymap

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

       Reads  a portable graymap as input.  Normalizes the contrast 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 out‐

       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.

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

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

       Copyright (C) 1989 by Jef Poskanzer.

			       28 February 1989			    pgmnorm(1)

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