Ppmbrighten User Manual(0) Ppmbrighten User Manual(0)NAMEppmbrighten - change a PPM image's Saturation and Value
SYNOPSISppmbrighten [-normalize] [-saturation [+|-saturation_percent]] [-value
[+|-value_percent]] ppmfile
Minimum unique abbreviation of option is acceptable. You may use dou‐
ble hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name from
its value.
DESCRIPTION
This program is part of Netpbm(1)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 meaning.
Value is a measure of how bright the color is, relative to some speci‐
fied maximum (the PPM format is also defined in terms of a specified
maximum brightness -- For the purposes of this program, they are the
same). In particular, it is the brightness of the brightest primary
color component of the color divided by the maximum brightness possible
for a component. Zero Value means black. White has full Value.
Hue is an indication of the secondary color with the same brightness
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 Satura‐
tion 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 sim‐
ply to increase the brightness of each pixel by a specified per cent‐
age, clipping each RGB component where the calculated brightness would
exceed full brightness. Thus, the brightest colors in the image would
change chromaticity in addition to not getting the specified brightness
boost. For decreasing brightness, pamfunc should do the same thing as
ppmbrighten.
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.
EXAMPLES
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
OPTIONS-value value_percent
This option specifies the amount, as a per centage, by which you
want to change the Value of each pixel. It may be negative.
-saturation value_percent
This option specifies the amount, as a per centage, by which you
want to change the Saturation of each pixel. It may be nega‐
tive.
-normalize
This option causes ppmbrighten to linearly remap the Values of
the pixels to cover the range 0 to 1. The option name is wrong
-- this operation is not normalization (it was named in error
and the name has been kept for backward compatibility).
ppmbrighten applies the brightening that you specify with the
-value option after the remapping.
Before Netpbm 10.14 (March 2003), your input must be from a
seekable file (not a pipe) to use -normalize. If it isn't, the
program fails with a bogus error message.
SEE ALSOpnmnorm(1) , ppmdim(1) , pamfunc(1) , ppmflash(1) , pamdepth(1) ,
pnmgamma(1) , ppmhist(1) , ppm(1)AUTHOR
Copyright (C) 1990 by Brian Moffet. Copyright (C) 1989 by Jef
Poskanzer.
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 26 October 2012 Ppmbrighten User Manual(0)
