[gdal-dev] Cannot set transparent color for GeoTIFFs processed by gdal_retile

Ralf Wagner rpw at globema.pl
Thu Feb 4 07:46:36 EST 2010


Thank you for your prompt answer.
Actually, I was experimenting with VRT files trying to fight this 
"transparency" problem. I have failed, but probably my way of setting 
transparency for VRT files was wrong - I had been setting 'c4' value 
(Alpha) for 'white' entry in color table in my VRT files to '0'. It 
didn't work. But if you are saying that this is way to go, I will try to 
do more experiments (and I will dig deeper into VRT format) .

Best regards,
Ralf Wagner

Chaitanya kumar CH pisze:
> Ralf,
>
> Try the -addalpha and -srcnodata options in gdalbuildvrt 
> (http://www.gdal.org/gdalbuildvrt.html) to generate a VRT file to 
> represent your files, individually or combined. Mention the RGB values 
> of the white pixels as -srcnodata values. This will add an alpha band 
> to your images and makes all white pixels transparent.
>
> Run gdal_retile.py using the vrt files.
>
> 2010/2/4 Ralf Wagner <rpw at globema.pl <mailto:rpw at globema.pl>>
>
>     Hello,
>     I am creating image pyramid from a bunch of color GeoTIFF files using
>     "gdal_retile" tool. I have managed to generate pyramid but
>     unfortunately
>     there is a problem - my GeoTIFFs maps overlap and have white margins
>     around and I am unable to force GDAL to treat white color as
>     transparent
>     to avoid covering maps by these margins. I have tried all ideas I
>     could
>     imagine but to no avail. So my question is: how to tweak "gdal_retile"
>     to get white color treated as transparent during merging?
>     I am using GDAL 1.6 on Windows. Any help will be very, very
>     appreciated
>     - thank you.
>
>     -- 
>     Ralf Wagner
>
>
>
>     _______________________________________________
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>     gdal-dev at lists.osgeo.org <mailto:gdal-dev at lists.osgeo.org>
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>
>
>
>
> -- 
> Best regards,
> Chaitanya kumar CH.
> /tʃaɪθənjə/ /kʊmɑr/
> +91-9848167848
> 17.241582N 80.142635E


-- 
Ralf Wagner



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tel. (+48) 22 848 73 13, fax (+48) 22 848 68 83
www.globema.com.pl <http://www.globema.com.pl>



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