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

       ppmbrighten - change a PPM image's Saturation and Value

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

       All options can be abbreviated to their shortest unique prefix.

       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 much total light intensity is in the color, relative to some specified maximum (the
       PPM format is also defined in terms of a specified maximum intensity -- For the purposes of this program,  they
       are  the  same).   In  particular, it is the intensity of the most intense primary color component of the color
       divided by the maximum intensity possible for a component.  Zero Value means black.  White has full Value.

       Hue is an indication of the secondary color with the same intensity 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 satu-
       ration 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 simply to increase  the  intensity  of  each
       pixel  by a specified per centage, clipping each RGB component where the calculated intensity would exceed full
       intensity.  Thus, the brightest colors in the image would change chromaticity in addition to  not  getting  the
       specified intensity 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 cen-
       tage closer to white.  This increases the value and saturation.

       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

       -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.

              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  -normal-
              ize.  If it isn't, the program fails with a bogus error message.

       pgmnorm(1), ppmdim(1), pamfunc(1), ppmflash(1), pamdepth(1), pnmgamma(1), ppmhist(1), ppm(1)

       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  copy-
       right  notice and this permission notice appear in supporting documentation.  This software is provided 'as is'
       without express or implied warranty.

netpbm documentation            09 January 2003     Ppmbrighten User Manual(0)