[gdal-dev] About palette/color table expansion

Matt Wilkie matt.wilkie at gov.yk.ca
Wed Aug 6 17:56:41 EDT 2008

Thanks Even!

This perfectly matches a task I have, and lets me cast half a dozen 
scripts I've created with the pctrgb workaround into the compost bin. :)

matt wilkie
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Information Management and Technology,
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax

Even Rouault wrote:
> Folks,
> just a few words to advertize the new capability of color table expansion that 
> has been added recently to GDAL trunk (1.6.0dev).
> A new option of gdal_translate, -expand rgb|rgba, enables the user to ask for 
> the expansion of a single band dataset with a color table and its translation 
> to a 3 or 4 band dataset with the R,G,B,A components. Usefull for output 
> drivers such as JPEG, JPEG2000, MrSID, ECW that don’t support color indexed 
> datasets.
> That capability relies on an extension of the VRTComplexSource that adds an 
> extra optionnal attribute  
> <ColorTableComponent>num_of_the_component</ColorTableComponent>.
> You can use color table expansion to warp color indexed datasets with 
> resampling methods more sophisticated than simple nearest neighbour, without 
> an intermediate file that would have been produced by pct2rgb for example.
> For example :
> gdal_translate -of VRT -expand rgb color_indexed.tif color_expanded.vrt
> gdalwarp -t_srs EPSG:32631 color_expanded.vrt color_expanded_warped.tif
> Regards.
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