Black alpha channels being replaced with white

Oct 7, 2014 at 7:12 PM
I am using Compress and SaveToDDS to batch convert a number of .TGA images to BC3. The images have glossiness in the alpha channel. Images that come in with completely black alpha channels are being saved with white alpha channels. If I add a single pixel of gray to the alpha they will compress correctly. It seems as if this is an optimization gone wrong, Is there any way to prevent this behavior?
Coordinator
Oct 21, 2014 at 5:13 AM
Edited Oct 21, 2014 at 7:33 AM
I'm not exactly sure what's happening here, but if you are using Resize or Convert on the image as part of this process, you may be hitting the 'premultiplied alpha' behavior of WIC. The texconv tool has a -sepalpha switch and the filter flag TEX_FILTER_SEPARATE_ALPHA both avoid this problem.

Otherwise, can you provide a repro example using texconv?