NAME

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

SYNOPSIS

          rgb2pct.py [-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.

       -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

       1998-2021

                                           Dec 27, 2021                                RGB2PCT(1)