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ppmnorm(1)									       ppmnorm(1)

       ppmnorm - normalize the contrast in a portable pixmap

       ppmnorm [-bpercent N | -bvalue N] [-wpercent N | -wvalue N] [ppmfile]

       Reads  a portable pixmap 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 pixmap as output.

       Works  by  computing  the  realtive grey-level of each pixel a'la ppmtopgm, and uses those
       values to scale the RGB levels.	Note that this is different from  using  pgmnorm  on  the
       individual red, green, and blue greymaps (as produced by ppmtorgb3) and recombining them.

       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
       ppmhist	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

       All flags can be abbreviated to their shortest unique prefix.

       pgmnorm(1), ppmhist(1), ppm(5)

       Wilson H. Bent. Jr. (whb@usc.edu), heavily based on the pgmnorm filter by Jef Poskanzer.

					  7 October 1993			       ppmnorm(1)
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