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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 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 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.


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