pgmnorm (1)
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
"contrast normalization"
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.
pgmhist
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
AUTHOR
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