[gdal-dev] Is Internal JPEG compression allowed on RGBA GeoTIFF?

[Daniele Romagnoli]

Dear all,
I was always thinking that JPEG doesn't support transparency so that it
would not be possible to convert a 4 bands GeoTIFF using JPEG compression
(without using internal binary mask).

However, I just did a gdal_translate -ot byte -scale -CO COMPRESS=JPEG
4bands.tif rgba_jpeg.tif and it "worked".

The gdalinfo output on the new file reports 4 bands dataset with
Gray,Green,Blue,Alpha colors.

Does the TIFF specification allows that?
I still have to read it again to check if/how alpha and JPEG compression
are related, but I'm wondering if you have any feedback on this topic in
order to understand if a "standard" GeoTIFF reader should be able to deal
with that or not and how to deal with the Alpha band (which at this point
would be a Lossy band, containing artifacts).

Feedbacks are welcome.
Regards,
Daniele










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Regards,
Daniele Romagnoli
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