ppmbrighten



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



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 maximum intensity -- For the purposes of this pro-
       gram, they are the same).  In particular, it is the  intensity  of  the
       most  intense primary color component of the color divided by the maxi-
       mum 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 indi-
       cated 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 Satura-
       tion 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 Saturation instead.

       For a simpler kind of brightening, you can use pamfunc -multiplier sim-
       ply 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 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  nega-
              tive.



       -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 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,  pro-
       vided  that  the  above  copyright notice appear in all copies and that
       both that copyright notice and this permission notice  appear  in  sup-
       porting  documentation.   This  software  is  provided  ’as is’ without
       express or implied warranty.



netpbm documentation            09 January 2003     Ppmbrighten User Manual(0)

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