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.TH "RGB2PCT" "1" "Aug 18, 2026" "" "GDAL"
.SH NAME
rgb2pct \- Convert a 24bit RGB image to 8bit paletted.
.SH SYNOPSIS
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.sp
.EX
rgb2pct [\-\-help] [\-\-help\-general] [\-\-creation\-option OPTION]
           [\-n colors | \-pct palette_file] [\-of format] <source_file> <dest_file>
.EE
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.SH DESCRIPTION
.sp
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.
.sp
\fBNOTE:\fP
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rgb2pct is a Python utility, and is only available if GDAL Python bindings are available.
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.sp
\fBTIP:\fP
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Equivalent in new \(dqgdal\(dq command line interface:
.sp
See \fI\%gdal raster rgb\-to\-palette\fP\&.
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.TP
.B \-\-help
Show this help message and exit
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.TP
.B \-\-help\-general
Gives a brief usage message for the generic GDAL commandline options and exit.
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.TP
.B \-n <color>
Select the number of colors in the generated
color table.  Defaults to 256.  Must be between 2 and 256.
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.TP
.B \-\-creation\-option OPTION
Optional creation parameters for the GeoTIFF driver,
for example \(dqCOMPRESS=LZW\(dq. Can be specified multiple times.
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.TP
.B \-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).
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.TP
.B \-of <format>
Select the output format. If not specified, the format is guessed from the
extension. Use the short format name. Only output formats
supporting pseudo\-color tables should be used.
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.TP
.B <source_file>
The input RGB file.
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.TP
.B <dest_file>
The output pseudo\-colored file that will be created.
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.SH RETURN STATUS CODE
.sp
The program returns status code 0 in case of success, and non\-zero in case of
error (non\-blocking errors emitted as warnings are considered as a successful
execution).
.SH EXAMPLE
.sp
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.
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.sp
.EX
$ rgb2pct \-pct palette.vrt rgb.tif pseudo\-colored.tif
$ more < palette.vrt
<VRTDataset rasterXSize=\(dq226\(dq rasterYSize=\(dq271\(dq>
    <VRTRasterBand dataType=\(dqByte\(dq band=\(dq1\(dq>
        <ColorInterp>Palette</ColorInterp>
        <ColorTable>
        <Entry c1=\(dq238\(dq c2=\(dq238\(dq c3=\(dq238\(dq c4=\(dq255\(dq/>
        <Entry c1=\(dq237\(dq c2=\(dq237\(dq c3=\(dq237\(dq c4=\(dq255\(dq/>
        <Entry c1=\(dq236\(dq c2=\(dq236\(dq c3=\(dq236\(dq c4=\(dq255\(dq/>
        <Entry c1=\(dq229\(dq c2=\(dq229\(dq c3=\(dq229\(dq c4=\(dq255\(dq/>
        </ColorTable>
    </VRTRasterBand>
</VRTDataset>
.EE
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.SH AUTHOR
Frank Warmerdam <warmerdam@pobox.com>
.SH COPYRIGHT
1998-2026
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