I have run into a problem using GDAL to read TIFF images with a alpha channels. GDAL returns the source TIFF sample values verbatim regardless of whether the alpha channel is associated (pre-multiplied) or unassociated within the TIFF image samples. (In each alpha model, the same pixel value with the same alpha value will have different sample values.)
GDAL does not appear to enforce a specific alpha model in its interface (pre-multiplied or non-pre-multiplied) and does not appear to offer any indication of which is currently being used. This creates a dead end as far as the GDAL interface goes. My system and most image formats (e.g., PNG) use the non-pre-multiplied alpha model. TIFF can use either. What is a user supposed to do about this? --------------------------+----------------------+-------------------------- Dr. Craig S. Bruce | Ph 819-771-8303 x205 | CubeWerx Inc. Senior Software Developer | Fax 819-771-8388 | Gatineau, Québec, Canada [email protected] | http://csbruce.com/ | http://www.cubewerx.com/ --------------------------+----------------------+-------------------------- "How many legs does a dog have if you call the tail a leg? Four. Calling a tail a leg doesn't make it a leg." -- Abraham Lincoln _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
