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Pamrecolor User Manual(0)						Pamrecolor User Manual(0)

       pamrecolor - alter colors without affecting luminance

       pamrecolor  [--colorspace=name]	[--rmult=fraction]  [--gmult=fraction] [--bmult=fraction]
       [--targetcolor=color] [--colorfile=file] [-randomseed=integer]


       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.

       This program is part of Netpbm(1)

       pamrecolor changes an image's colors to be as close as possible to given target colors but
       with  the  constraint that the luminance not be modified.  That is, the original image and
       the target image will look identical if both are converted to grayscale	(e.g.  with  ppm-
       topgm(1)  ).   You can have pamrecolor select target colors randomly, specify a single hue
       for the entire image, or take the target colors from a target image.

       pamrecolor works on pseudo-Netpbm images based on arbitrary color spaces.  You can  define
       the color space explicitly or choose on of many that pamrecolor knows by name.

       The  output  is	a  PAM image on standard output.  Options control the exact format of the
       PAM.  If you want a PNM (PBM, PGM, or PPM) image, use pamtopnm(1)
	on the output.	There is no need to convert if you will use the image as input to a  cur-
       rent Netpbm program, but many other programs don't know what a PAM is.

	      Designate  the  color space to use for determining the contribution to luminance of
	      each of the red, green, and blue color channels.	For example, in the SMPTE-C color
	      space  an  RGB  color  is  converted to grayscale by multiplying the red channel by
	      0.2124132, the green channel by 0.7010437, and the blue channel  by  0.0865432  and
	      summing the resulting three products.

	      When  you  use this option, the input and output images are not true Netpbm images,
	      because the Netpbm image format specifies a particular color space.   Instead,  you
	      are  using  a variation on the format in which the sample values in the raster have
	      different meaning.  Many programs that ostensibly use Netpbm images actually use	a
	      variation  with  a different color space, For example, GIMP <http://www.gimp.org/>
	      uses sRGB internally and if you have GIMP generate a Netpbm image file,  it  really
	      generates a variation of the format that uses sRGB.

	      pamrecolor knows the following color spaces (name values):


	      Adobe RGB (1998) with a D65 reference white


	      Apple  RGB with a D65 reference white


	      CIE with an Illuminant E reference white


	      NTSC RGB with an Illuminant C reference white


	      PAL/SECAM with a D65 reference white


	      SMPTE-C with a D65 reference white


	      sRGB with a D65 reference white


	      Wide-gamut RGB with a D50 reference white

	      The  default  is <q>ntsc</q> because this is the color space that the Netpbm format
	      of  Netpbm  and  many  other  graphics  utilities.   As  a   counterexample,   GIMP
	      <http://www.gimp.org/>  uses sRGB as its native color space.

	      The  luminance  values  pamrecolor uses for each of the above come from Bruce Lind-
	      bloom's  Computing RGB-to-XYZ and XYZ-to-RGB matrices (1)



	      Instead of selecting a color space by name, you can specify explicitly the  contri-
	      bution  of each color channel to the overall luminance as red, green, and blue mul-
	      tipliers.  These three options must be used together, and the three fraction values
	      must  sum to 1.0.  For example, you can specify the ProPhoto (ROMM) RGB color space
	      with <q>--rmult=0.2880402 --gmult=0.7118741 --bmult=0.0000857</q>.

	      Designate color as the target color for the image.  pamrecolor will make each pixel
	      as  close  as  possible  to color subject to the constraint that the luminance must
	      stay the same as in the original image.  Specify color as in the	argument  of  the
	      ppm_parsecolor()	library routine <libppm.html#colorname>  (e.g., <q>hotpink</q> or

	      If you specify neither --targetcolor  nor  --colorfile,  pamrecolor  will  randomly
	      select a target color for each pixel of the input image.

	      You may not specify both -targetcolor and -colorfile.

	      Take per-pixel target colors from Netpbm file file instead of using a single target
	      color for the entire image.  file should be a PPM or color PAM image.  If the image
	      in the file wider or taller than the input image, pamrecolor uses only the left and
	      top part of it.  If the image is narrower  or  shorter,  pamrecolor  considers  the
	      image to be repeated in a tile pattern.

	      If  you  specify	neither  --targetcolor	nor --colorfile, pamrecolor will randomly
	      select a target color for each pixel of the input image.

	      You may not specify both -targetcolor and -colorfile.

	      This is the seed for the random number generator that generates the pixels.

	      Use this to ensure you get the same image on separate invocations.

	      By default, pamrecolor uses a seed derived from the time of  day	and  process  ID,
	      which gives you fairly uncorrelated results in multiple invocations.

	      This option was new in Netpbm 10.61 (December 2012).

       This command tints an image yellow:

	   pamrecolor --targetcolor=yellow colorpic.pam > yellowpic.pam

       This command takes the colors from colorpicture.ppm and applies them to graypicture.pgm:

	   pamrecolor --colorfile=colorpic.ppm graypic.pgm > colorizedpic.pam

       The  grayscale  version of colorizedpic.pam will look just like graypic.pgm.  Note that if
       you use a non-Netpbm tool to do the conversion to grayscale, you may additionally need  to
       specify an appropriate --colorspace value for your conversion tool.

       Here are a couple of fun special effects you can produce with pamrecolor:

       o      Specify a color file that is identical to the input image but with some large, col-
	      ored text added to it.  The text will <q>magically</q> vanish  when  the	image  is
	      converted to grayscale.

       o      Provide  a low-contrast grayscale image &mdash; perhaps a secret message written in
	      similar shades of gray &mdash; as the input file and a colorful but completely dif-
	      ferent image as the color file.  If done carefully, the grayscale image can be hid-
	      den by the colorful image.  Only people who know to convert the result to grayscale
	      can recover the original grayscale image.

       o      Use  --targetcolor=tan to make an image look like an old-timey photograph (or, more
	      precisely,		 a		   sepia-toned		       photograph
	      <http://en.wikipedia.org/wiki/Photographic_print_toning>	of the late 1800s).

       Scott Pakin wrote pamrecolor in July 2010.

       pamrecolor was new in Netpbm 10.52 (September 2010).

       Copyright (C) 2010 Scott Pakin, scott+pbm@pakin.org.







netpbm documentation			   31 July 2010 		Pamrecolor User Manual(0)
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