ppmbrighten(1) - phpMan

Ppmbrighten User Manual(0) Ppmbrighten User Manual(0)

NAME
ppmbrighten - change a PPM image's Saturation and Value

SYNOPSIS
ppmbrighten [-normalize] [-saturation [+|-saturation_percent]] [-value [+|-value_percent]]
ppmfile

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.

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 parame-
ters.

You can also remap the colors of the pixels so their Values cover the full range of possi-
ble 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 capital-
ize 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 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 com-
ponent. 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%), 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 Sat-
uration instead.

For a simpler kind of brightening, you can use pamfunc -multiplier simply to increase the
brightness of each pixel by a specified per centage, 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 negative.

-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 mes-
sage.

SEE ALSO
pnmnorm(1), ppmdim(1), pamfunc(1), ppmflash(1), pamdepth(1), pnmgamma(1), ppmhist(1),
ppm(1)

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.

DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master
documentation is at

http://netpbm.sourceforge.net/doc/ppmbrighten.html

netpbm documentation 26 October 2012 Ppmbrighten User Manual(0)

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