ppmnorm

 

---

 ppmnorm(1)                                             ppmnorm(1)
 
 
 
NAME
        ppmnorm - normalize the contrast in a portable pixmap
 
SYNOPSIS
        ppmnorm  [-bpercent  N | -bvalue N] [-wpercent N | -wvalue
        N] [ppmfile]
 
DESCRIPTION
        Reads a portable pixmap as input.  Normalizes the contrast
        by  forcing the lightest pixels to white, the darkest pix­
        els 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 lev­
        els.   Note  that  this is different from using pgmnorm on
        the individual red, green, and blue greymaps (as  produced
        by ppmtorgb3) and recombining them.
 
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  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 bvalue.
 
        All flags can be abbreviated to their shortest unique pre­
        fix.
 
SEE ALSO
        pgmnorm(1), ppmhist(1), ppm(5)
 
AUTHOR
        Wilson H. Bent. Jr. (whb@usc.edu), heavily  based  on  the
        pgmnorm filter by Jef Poskanzer.
 
 
 
                           7 October 1993               ppmnorm(1)

---