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pgmnorm.1
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pgmnorm(1) USER COMMANDS pgmnorm(1)
NAME
pgmnorm - normalize the contrast in a portable graymap
SYNOPSIS
pgmnorm [-bpercent _✓N | -bvalue _✓N] [-wpercent _✓N | -wvalue _✓N]
[_✓p_✓g_✓m_✓f_✓i_✓l_✓e]
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
_✓p_✓g_✓m_✓h_✓i_✓s_✓t 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 _✓b_✓v_✓a_✓l_✓u_✓e. If you want to lighten the image,
then set _✓b_✓v_✓a_✓l_✓u_✓e to 0 and just fiddle with _✓w_✓v_✓a_✓l_✓u_✓e; similarly,
to darken the image, set _✓w_✓v_✓a_✓l_✓u_✓e to maxval and play with
_✓b_✓v_✓a_✓l_✓u_✓e.
All flags can be abbreviated to their shortest unique pre-
fix.
SEE ALSO
pgmhist(1), pgm(5)
AUTHOR
Partially based on the fbnorm filter in Michael Mauldin's
"Fuzzy Pixmap" package.
Copyright (C) 1989 by Jef Poskanzer.
Sun Release 4.0 Last change: 28 February 1989 1