On Mon, 2004-05-10 at 17:42, David Christian Berg wrote:
Hi guys,
I'm using the build from 6th of May... and the export of gradient with transparency is somewhat messed up when you make excessive use of it... it works fine, if you have a background color to export. picture one is with white as bg color exported, picture two is with the background filled in gimp.
Looks like we're exporting PNGs with premultiplied alphas. Bad.
As I recall, we were having problems with similar glitches happening when rendering <images>. The problem is that the libnr renderer can only do image compositing to premultiplied destination buffers.
We switched to using premultiplied alpha for the export buffer and that fixed that problem -- but created this one. I should have seen it coming...
At the moment I think the best we can do is un-premultiply the alphas in the buffer before writing the PNG. We'll have lost some precision (with resultant banding), but I think that's the best fix on short order.
Does anybody have the same problem or can reproduce it?
Haven't tried yet. That's my guess from memory.
-mental