pambrighten - change a PPM image's Saturation and Value

       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 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.

       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

netpbm documentation                             18 August 2020                       PambrightenUserManual(1)

       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

pambrighten was new in Netphm 10.86 (March 2019).  It was a PAM conversion of the much older ppmbrighten.

       pambrighten - change a PPM image's Saturation and Value

       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 [-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.