[Gdal-dev] Reducing geotiff colors to a standard LUT

Zhonghai Wang zhonghaiw at gmail.com
Wed Jul 5 02:50:43 EDT 2006

Hi Jed,

I've got the same problem with my TIFFs, but in my case they are 24bit RGB
images. I tried to adjust the colors and then merge them. I even convert
them to 8bit images with LUTs, but I failed.

AFAIK, you can merge them together under the RGB model with the GDAL
commands like:

1. pct2rgb.py
2. gdal_merge.py
3. rgb2pct.py

but I don't know if this really works. IMO, you may get some troubles with
the command rgb2pct.py.

help this can help.


On 7/4/06, Jed O. Kaplan <jed.kaplan at ips.unibe.ch> wrote:
> Hello all,
> I have a series of geotiff files that are 8-bit paletted pseudocolor
> images. Unfortunately each separate image file has a different color
> table, though they are a sort of DRGs so the original scans have
> approximately all the same colors.
> I would like to convert all the images to have a standard color
> table, so that, e.g., I can merge the files into a single image,
> perform GIS operations, etc.
> Is there any way using GDAL tools or the API that I can give all of
> my individual images the same color table?  The image files are large
> (ca. 2000x3000 pixels), but I can convert them temporarily to full
> color rgb images and then reduce the colors.  I have a standard color
> table in another geotiff file.
> I have tried to do this using the imagemagick tool: convert -map
> <file> <infile> <outfile> but this process is impossibly slow.
> Any suggestions for (standardized, semi-automated) color reduction
> for DRG's would be much appreciated.
> Thanks,
> Jed Kaplan
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> Gdal-dev at lists.maptools.org
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