RGB2PCT(1) GDAL RGB2PCT(1)
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 dif-
fusion) to maximize output image visual quality.
-n <color>
Select the number of colors in the generated color table. De-
faults 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 speci-
fied, the format is guessed from the extension (previously was
GTiff). Use the short format name. Only output formats support-
ing 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 cre-
ated 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)
Generated by dwww version 1.14 on Fri Jan 24 06:27:43 CET 2025.