[gdal-dev] Color-palette file for use in rgb2pct

[Frank Warmerdam]

Luuk Schaminee wrote:
> Hi,
> 
> I am trying to convert a 24 bit RGB TIFF file to a 8 bit TIFF file. Without the –pct option this works perfectly but I want to control the created colors with a palette file. So I tried the following command:
> rgb2pct -pct c:\color_file.txt c:\image.tif e:\new_image.tif.
...
> So now my question. What format must the palette file be in? and can you give me a working example.

Luuk,

The palette must be in a GDAL supported raster file format (ie. TIFF,
PNG, GIF, etc).  Likely the easiest format for you to prepare manually
would be VRT format.  The following VRT is one with a small color table
and no actual raster data:


<VRTDataset rasterXSize="226" rasterYSize="271">
   <Metadata/>
   <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>

The c1/c2/c3/c4 entries are the red, green, blue and alpha components
of color entries.  You can have up to 256 entries in a normal file.

Best regards,
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