rgb2pct(1)rgb2pct(1)NAMErgb2pct - 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 colors:
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 a raster file in a GDAL supported format
with a palette.
-of format:
Format to generated (defaults to GeoTIFF). Same semantics as the
-of flag for gdal_translate. 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
GDAL Sun Dec 17 2017 rgb2pct(1)