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Pnmremap User Manual(0) 						  Pnmremap User Manual(0)

NAME
       pnmremap - replace colors in a PNM image with colors from another set

SYNOPSIS
       pnmremap

       -mapfile=palettefile

       [-floyd|-fs|-nfloyd|-nofs]

       [-norandom]

       [-firstisdefault]

       [-verbose]

       [-missingcolor=color]

       [pnmfile]

       All  options  can be abbreviated to their shortest unique prefix.  You may use two hyphens
       instead of one to designate an option.  You may use either white space or an  equals  sign
       between an option name and its value.

DESCRIPTION
       This program is part of Netpbm(1)

       pnmremap  replaces  the	colors	in  an input image with those from a palette you specify.
       Where colors in the input are present in the palette, they just stay the same in the  out-
       put.   But where the input contains a color that is not in the palette, pnmremap gives you
       these choices:

       o      Choose the closest color from the palette.

       o      Choose the first color from the palette.

       o      Use a color specified by a command option (-missing).

       o      Dither.  This means rather than mapping pixel by pixel, pnmremap uses  colors  from
	      the  palette to try to make multi-pixel regions of the output have the same average
	      color as the input (for another kind of dithering, see ppmdither).

       Two reasons to use this program are: 1) you want to reduce the number  of  colors  in  the
       input  image;  and 2) you need to feed the image to something that can handle only certain
       colors.

       To reduce colors, you can generate the palette with pnmcolormap.

       By default, pnmremap maps an input color that is not in the palette to the  closest  color
       that  is  in  the palette.  Closest means with the smallest Cartesian distance in the red,
       green, blue brightness space (smallest sum of the  squares  of  the  differences  in  red,
       green, and blue ITU-R Recommendation BT.709 gamma-adjusted intensities).

       You  can  instead  specify a single default color for pnmremap to use for any color in the
       input image that is not in the palette.	Use the -missing option for this.

       You can also specify that the first color in the palette image is the  default.	 Use  the
       -firstisdefault option for this.

       The  palette  is simply a PNM image.  The colors of the pixels in the image are the colors
       in the palette.	Where the pixels appear in the image, and the dimensions  of  the  image,
       are  irrelevant.  Multiple pixels of the same color are fine.  However, a palette image is
       typically a single row with one pixel per color.

       If you specify -missing, the color you so specify is in the palette in addition	to  what-
       ever is in the palette image.

       For  historical	reasons,  Netpbm sometimes calls the palette a 'colormap.' But it doesn't
       really map anything.  pnmremap creates its own map, based on the palette,  to  map  colors
       from the input image to output colors.

   Palette/Image Type Mismatch
       In  the simple case, the palette image is of the same depth (number of planes, i.e. number
       of components in each tuple (pixel)) as the input image and pnmremap just does a straight-
       forward	search	of  the  palette for each input tuple (pixel).	In fact, pnmremap doesn't
       even care if the image is a visual image.

       But what about when the depths differ?  In that case, pnmremap converts	the  input  image
       (in its own memory) to match the palette and then proceeds as above.

       There  are only two such cases in which pnmremap knows how to do the conversion:  when one
       of them is tuple type RGB, depth 3, and the other is tuple  type  GRAYSCALE  or	BLACKAND-
       WHITE, depth 1; and vice versa.

       In any other case, pnmremap issues and error message and fails.

       Note  that  as long as your input and palette images are PNM, they'll always fall into one
       of the cases pnmremap can handle.  There's an issue only if you're using some  exotic  PAM
       image.

       Before  Netpbm  10.27  (March  2005),  pnmremap	could not handle the case of a palette of
       greater depth than the input image.  (It would issue an error message  and  fail  in  that
       case).	You can use ppmtoppm to increase the depth of the input image to work around this
       limitation.

       In any case, the output image has the same tuple type and depth as the palette image.

   Multiple Image Stream
       pnmremap handles a multiple image input stream, producing a multiple image output  stream.
       The input images need not be similar in any way.

       Before Netpbm 10.30 (October 2005), pnmremap ignored any image after the first.

   Examples
       pnmcolormap testimg.ppm 256 >palette.ppm

       pnmremap -map=palette.ppm testimg.ppm >reduced_testimg.ppm

       To  limit  colors to a certain set, a typical example is to create an image for posting on
       the World Wide Web, where different browsers know different colors.  But all browsers  are
       supposed  to  know  the 216 'web safe' colors which are essentially all the colors you can
       represent in a PPM image with a maxval of 5.  So you can do this:

       pamseq 3 5 >websafe.pam

       pnmremap -map=websafe.pam testimg.ppm >websafe_testimg.ppm

       Another useful palette is one for the 8 color IBM TTL color set, which you can create with
       pamseq 3 1 >ibmttl.pam

       If you want to quantize one image to use the colors in another one, just  use  the  second
       one  as	the  palette.	You don't have to reduce it down to only one pixel of each color,
       just use it as is.

       The output image has the same type and maxval as the palette image.

PARAMETERS
       There is one parameter, which is required: The file specification of the input PNM file.

OPTIONS
       -mapfile=palettefilename
	      This names the file that contains the palette image.

	      This option is mandatory.

       -floyd

       -fs

       -nofloyd

       -nofs  These options determine whether pnmremap does Floyd-Steinberg  dithering.   Without
	      Floyd-Steinberg, pnmremap selects the output color of a pixel based on the color of
	      only the corresponding  input  pixel.   With  Floyd-Steinberg,  pnmremap	considers
	      regions of pixels such that the average color of a region is the same in the output
	      as in the input.	The dithering effect appears as a dot pattern up close, but  from
	      a  distance,  the  dots  blend  so that you see more colors than are present in the
	      color map.

	      As an example, if your color map contains only black and white, and the input image
	      has  4 adjacent pixels of gray, pnmremap with Floyd-Steinberg would generate output
	      pixels black, white, black, white, which from a distance looks gray.   But  without
	      Floyd-Steinberg,	pnmremap  would  generate 4 white pixels, white being the single-
	      pixel approximation of gray.

	      Floyd-Steinberg gives vastly better results on images where unmodified quantization
	      has  banding  or other artifacts, especially when going to a small number of colors
	      such as the above IBM set.  However, it does take substantially more CPU time.

	      -fs is a synonym for -floyd.  -nofs is a synonym for -nofloyd.

	      The default is -nofloyd.

	      Before Netpbm 10.46 (March 2009), dithering doesn't work quite as you expect if the
	      color map has a lower maxval than the input.  pnmremap reduces the color resolution
	      to the color map's maxval before doing any dithering, so	the  dithering	does  not
	      have  the  effect  of  making the image, at a distance, appear to have the original
	      maxval.  In current Netpbm, it does.

       -norandom
	      This option affects a detail of the Floyd-Steinberg dithering process.  It  has  no
	      effect if you aren't doing Floyd-Steinberg dithering.

	      By default, pnmremap initializes the error propagation accumulator to random values
	      to avoid the appearance of unwanted patterns.  This is an extension of the original
	      Floyd-Steinberg algorithm.

	      A  drawback  of  this is that the same pnmremap on the same input produces slightly
	      different output every time, which makes comparison difficult.

	      With -norandom, pnmremap initializes the error accumulators to zero and the  output
	      is completely predictable.

	      -norandom was new in Netpbm 10.39 (June 2007).

       -firstisdefault
	      This  tells pnmremap to map any input color that is not in the palette to the first
	      color in the palette (the color of the pixel in the top left corner of the  palette
	      image)

	      See DESCRIPTION <#description> .

	      If  you  specify -firstisdefault, the maxval of your input must match the maxval of
	      your palette image.

       -missingcolor=color
	      This specifies the default color for pnmremap to map to a color in the input  image
	      that  isn't  in  the  palette.  color may or may not be in the palette image; it is
	      part of the palette regardless.

	      If you specify -missingcolor, the maxval of your input must  match  the  maxval  of
	      your palette image.

       -verbose
	      Display helpful messages about the mapping process.

SEE ALSO
       pnmcolormap(1)  ,  pamseq(1) , pnmquant(1) , ppmquantall(1) , pamdepth(1) , ppmdither(1) ,
       ppmquant(1) , ppm(1)

HISTORY
       pnmremap first appeared in Netpbm 9.23 (January 2002).	Before	that,  its  function  was
       available  only as part of the function of pnmquant (which was derived from the much older
       ppmquant).  Color quantization really has two main subfunctions, so Netpbm 9.23	split  it
       out  into  two  separate  programs: pnmcolormap and pnmremap and then Netpbm 9.24 replaced
       pnmquant with a program that simply calls pnmcolormap and pnmremap.

AUTHOR
       Copyright (C) 1989, 1991 by Jef Poskanzer.

netpbm documentation			   03 June 2009 		  Pnmremap User Manual(0)
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