ppmbrighten [-normalize] [-saturation [+|-saturation_percent]] [-value
All options can be abbreviated to their shortest unique prefix.
This program is part of Netpbm.
ppmbrighten increases or decreases the Saturation and Value (from the
HSV color space) of each pixel of a PPM image. You specify the per
centage change for each of those parameters.
You can also remap the colors of the pixels so their Values cover the
full range of possible Values.
Hue-Saturation-Value, or HSV, is one way to represent a color, like
the more well-known RGB. Hue, Saturation, and Value are numbers in
the range from 0 to 1. We always capitalize them in this document
when we mean the number from the HSV color space, especially since
"value" as a conventional English word has a much more abstract mean-
Value is a measure of how much total light intensity is in the color,
relative to some specified maximum (the PPM format is also defined in
terms of a specified maximum intensity -- For the purposes of this
program, they are the same). In particular, it is the intensity of
the most intense primary color component of the color divided by the
maximum intensity possible for a component. Zero Value means black.
White has full Value.
Hue is an indication of the secondary color with the same intensity
that most closely approximates the color. A secondary color is made
of a combination of at most two of the primary colors.
Saturation is a measure of how close the color is to the color indi-
cated by the Hue and Value. A lower number means more light of the
third primary color must be added to get the exact color. Full Satu-
ration means the color is a secondary color. Zero Saturation means
the color is gray (or black or white). Decreasing the saturation of a
color tends to make it washed out.
If it is impossible to increase the Value of a pixel by the amount you
specify (e.g. the Value is .5 and you specify +200%), ppmbrighten
increases it to full Value instead.
If it is impossible to increase the Saturation of a pixel by the
amount you specify (e.g. it is already half saturated and you specify
+200%), ppmbrighten increases it to full Saturation instead.
For a simpler kind of brightening, you can use pamfunc -multiplier
simply to increase the intensity of each pixel by a specified per cen-
tage, clipping each RGB component where the calculated intensity would
exceed full intensity. Thus, the brightest colors in the image would
change chromaticity in addition to not getting the specified intensity
boost. For decreasing brightness, pamfunc should do the same thing as
ppmflash does another kind of brightening. It changes the color of
each pixel to bring it a specified per centage closer to white. This
increases the value and saturation.
To double the Value of each pixel:
ppmbrighten -v 100
To double the Saturation and halve the value of each pixel:
ppmbrighten -s 100 -v -50
pgmnorm, ppmdim, pamfunc, ppmflash, pamdepth,
pnmgamma, ppmhist, ppm
Copyright (C) 1990 by Brian Moffet. Copyright (C) 1989 by Jef
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted, pro-
vided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in sup-
porting documentation. This software is provided 'as is' without
express or implied warranty.
netpbm documentation 09 January 2003 Ppmbrighten User Manual(0)