GTiff: Use EXTRASAMPLE_UNASSALPHA by default (behaviour change w.r.t. previous GDAL versions)
|Reported by:||Even Rouault||Owned by:||warmerdam|
This was discussed in this email http://lists.osgeo.org/pipermail/gdal-dev/2012-May/032968.html and the subsequent thread.
The new behaviour is the following : when before, EXTRASAMPLE_ASSALPHA (=premultiplied) was used, we will now write EXTRASAMPLE_UNASSALPHA (=non-premultiplied), which better reflects the expected behaviour of writting applications.
This can however be altered by setting the ALPHA creation option to PREMULTIPLIED.
The ALPHA creation option now accepts :
- YES : EXTRASAMPLE_UNASSALPHA (was EXTRASAMPLE_ASSALPHA in GDAL < 2.0)
- PREMULTIPLIED: EXTRASAMPLE_ASSALPHA
- NON-PREMULTIPLIED: EXTRASAMPLE_UNASSALPHA
- UNSPECIFIED or NO : EXTRASAMPLE_UNSPECIFIED
This is only a change in writting mode. There is no change in reading mode (and in particular, there is no special processing of premultiplied)