#4733 closed defect (fixed)
GTiff: Use EXTRASAMPLE_UNASSALPHA by default (behaviour change w.r.t. previous GDAL versions)
Reported by: | Even Rouault | Owned by: | warmerdam |
---|---|---|---|
Priority: | normal | Milestone: | 1.10.0 |
Component: | GDAL_Raster | Version: | unspecified |
Severity: | normal | Keywords: | gtiff alpha |
Cc: |
Description
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)
r24653 /trunk/gdal/frmts/gtiff/geotiff.cpp: GTiff: Use EXTRASAMPLE_UNASSALPHA by default (behaviour change w.r.t. previous GDAL versions) (#4733)
r24654 /trunk/autotest/gcore/data/ (3 files): Update test images to use EXTRASAMPLE_UNASSALPHA (#4733)