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 ppm-
       brighten.

       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),	  pamdepth(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)