NAME

       rgb2pct - Convert a 24bit RGB image to 8bit paletted.

SYNOPSIS

          rgb2pct [--help] [--help-general]
                     [-n colors | -pct palette_file] [-of format] <source_file> <dest_file>

DESCRIPTION

       This  utility  will  compute  an  optimal pseudo-color table for a given RGB image using a
       median cut algorithm on a downsampled RGB histogram.   Then it converts the image  into  a
       pseudo-colored  image  using  the  color  table.  This conversion utilizes Floyd-Steinberg
       dithering (error diffusion) to maximize output image visual quality.

       NOTE:
          rgb2pct is a Python utility,  and  is  only  available  if  GDAL  Python  bindings  are
          available.

       --help Show this help message and exit

       --help-general
              Gives a brief usage message for the generic GDAL commandline options and exit.

       -n <color>
              Select  the  number of colors in the generated color table.  Defaults to 256.  Must
              be between 2 and 256.

       -pct <palette_file>
              Extract the color table from <palette_file> instead of computing it.  Can  be  used
              to  have  a  consistent color table for multiple files.  The <palette_file> must be
              either a raster file in a GDAL supported format with a palette or a color file in a
              supported format (txt, qml, qlr).

       -of <format>
              Select  the  output format. Starting with GDAL 2.3, if not specified, the format is
              guessed from the extension (previously was GTiff). Use the short format name.  Only
              output formats supporting pseudo-color tables should be used.

       <source_file>
              The input RGB file.

       <dest_file>
              The output pseudo-colored file that will be created.

EXAMPLE

       If  it  is desired to hand create the palette, likely the simplest text format is the GDAL
       VRT format.  In the following example a VRT was created in a text editor with  a  small  4
       color  palette  with the RGBA colors 238/238/238/255, 237/237/237/255, 236/236/236/255 and
       229/229/229/255.

          rgb2pct -pct palette.vrt rgb.tif pseudo-colored.tif
          more < palette.vrt
          <VRTDataset rasterXSize="226" rasterYSize="271">
              <VRTRasterBand dataType="Byte" band="1">
                  <ColorInterp>Palette</ColorInterp>
                  <ColorTable>
                  <Entry c1="238" c2="238" c3="238" c4="255"/>
                  <Entry c1="237" c2="237" c3="237" c4="255"/>
                  <Entry c1="236" c2="236" c3="236" c4="255"/>
                  <Entry c1="229" c2="229" c3="229" c4="255"/>
                  </ColorTable>
              </VRTRasterBand>
          </VRTDataset>

AUTHOR

       Frank Warmerdam <warmerdam@pobox.com>

COPYRIGHT

       1998-2024

                                           Nov 01, 2024                                RGB2PCT(1)