NAME

       pambrighten - change a PPM image's Saturation and Value

SYNOPSIS

       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.

DESCRIPTION

       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.

EXAMPLES

       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

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common Options ⟨index.html#commonoptions⟩ ), 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.

SEE ALSO

       pnmnorm(1), ppmdim(1), pamfunc(1), ppmflash(1),  pamaltsat(1),  pamdepth(1),  pnmgamma(1),
       pamhue(1), ppmhist(1), ppm(1)

HISTORY

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

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, 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/pambrighten.html