NAME

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

SYNOPSIS

          rgb2pct.py [--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.

       --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.

       NOTE: rgb2pct.py is a Python script, and will only work if GDAL was built with Python support.

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.py -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

                                                  Feb 08, 2024                                        RGB2PCT(1)