[gdal-dev] gtiff with internal mask

[Even Rouault]

Le mardi 16 juillet 2013 12:29:37, Duarte Carreira a écrit :
> I'm trying to create gtiffs with transparent areas where there are voids
> between my original images.
> 
> I have successfully done it by using an alpha band but this process created
> 3x larger images. I think partly because of an additional 4th band and
> partly because I cannot use ycbcr to compress with jpeg. So I thought of
> using internal masks expecting to get smaller images but cannot get it to
> work.
> 
> When converting from the rgba image using -mask 4 I cannot "see" the
> transparency and get black areas:
> 
> gdal_translate -b 1 -b 2 -b 3 -ma sk 4 --config GDAL_TIFF_INTERNAL_MASK YES
> test_alpha.tif test_internalmask.tif
> 
> I tried looking at the images using qgis and paint.net.

I know QGIS doesn't use the GDALGetMaskBand() API, so no real surprise (that 
would likely be a possible QGIS enhancement). And paint.net probably doesn't 
support this feature of the TIFF format either.

MapServer does support mask bands however.

For QGIS, you could workaround that however. Imagine that you have a YCbCr 
TIFF + internal mask in.tif.

You can do : "gdal_translate -of VRT -b 1 -b 2 -b 3 -b mask in.tif out.vrt"

And QGIS should handle out.vrt as a regular RGBA dataset.

> 
> Any hints or help appreciated.
> 
> Thanks,
> Duarte
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> Duarte Carreira
> Diretor | Dep. Informa??o Geogr?fica e Cartografia
> 
> www.edia.pt<http://www.edia.pt>
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