pambrighten - change a PPM image's Saturation and Value
pambrighten [
-saturation=[
+|
-]
saturation_percent] [
-value=[
+|
-]
value_percent] [
netpbmfile]
Minimum unique abbreviation of option is acceptable. You may use double 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.
This program is part of
Netpbm(1).
pambrighten increases or decreases the Saturation and Value (from the HSV
color space) of each pixel of a Netpbm image. You specify the percentage
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.
The input image is from the file named
netpbmfile, or Standard Input if
netpbmfile is not specified.
The output format is the same as the input format and any extra channels, such
as transparency, are passed through.
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 specified
maximum (the Netpbm formats are 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 indicated 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 Saturation 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%),
pambrighten 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%),
pambrighten increases it to full Saturation instead.
For a simpler kind of brightening, you can use
pamfunc -multiplier simply
to increase the brightness of each pixel by a specified percentage, 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
pambrighten.
ppmflash does another kind of brightening. It changes the color of each
pixel to bring it a specified percentage closer to white. This increases the
value and saturation.
pambrighten is meant to replace
ppmbrighten. It is the same as
ppmbrighten, except that it recognizes the various Netpbm image formats
rather than treating them all as PPM. The output format is the same as the
input format and extra channels in a PAM image (such as a transparency
channel) get passed through.
If you want to modify the hues in the image, use
pamhue.
To double the Value of each pixel:
pambrighten -value=100
To double the Saturation and halve the Value of each pixel:
pambrighten -saturation=+100 -value=-50
In addition to the options common to all programs based on libnetpbm (most
notably
-quiet, see
Common Options ),
pambrighten recognizes the following command line
options:
-
-value=value_percent
- This option specifies the amount, as a percentage, by which
you want to increase the Value of each pixel. It may be negative.
The default is zero.
-
-saturation=value_percent
- This option specifies the amount, as a percentage, by which
you want to increase the Saturation of each pixel. It may be negative.
The default is zero.
pnmnorm(1),
ppmdim(1),
pamfunc(1),
ppmflash(1),
pamaltsat(1),
pamdepth(1),
pnmgamma(1),
pamhue(1),
ppmhist(1),
ppm(1)
pambrighten was new in Netphm 10.86 (March 2019). It was a PAM conversion
of the much older
ppmbrighten.
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, provided that
the above copyright notice appear in all copies and that both that copyright
notice and this permission notice appear in supporting documentation. This
software is provided "as is" without express or implied warranty.
This manual page was generated by the Netpbm tool 'makeman' from HTML source.
The master documentation is at
- http://netpbm.sourceforge.net/doc/pambrighten.html