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



Table Of Contents


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


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


OPTION USAGE
       All options can be abbreviated to their shortest  unique
       prefix.


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 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 maxi-
       mum 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 compo-
       nent.  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 com-
       ponent 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 sat-
       uration.


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  cent-
              age,  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  cent-
              age,  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 remap-
              ping.

              Before Netpbm 10.14 (March 2003), your input must
              be from a seekable file (not a pipe) to use -nor-
              malize.  If it isn't, the program  fails  with  a
              bogus error message.




SEE ALSO
       pgmnorm(1),    ppmdim(1),    pamfunc(1),    ppmflash(1),
       pnmdepth(1), pnmgamma(1), ppmhist(1), ppm(1)


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.



netpbm documentation    09 January 20Ppmbrighten User Manual(0)
