Hi there,
We have been creating a node structure in the compositor for the conversion of blender vector pass output to RSMB vector pass (its a after effects plugin for motion blur) in this thread -- http://blenderartists.org/forum/showthread.php?265887 ... I have created the node structure, but have come across a strange bug...
the alpha output of the image should be 1.0 as the combine rgba node has alpha set at 1.0... even if i hook in the original alpha into the alpha slot, the alpha channel is still messed up. It seems that this only happens at render time... the viewer node reports it correctly but not when you hit f12
I have attached the example file & screenshot
Regards
Carlo
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This is a known issue in Blender's viewers and it's already in the color TODO.
Viewers and 3D views are currently expecting unassociated (not premultiplied) alpha for RGBA images.
This can be particularly misleading if you need associated (premultiplied) alpha in the output but you didn't multiply that alpha in your compositing tree. The viewer set in RGBA shows the correct appearance but the RGB and the output look wrong.
This is not a bug, but a missing feature (alpha consistency accross viewers). As I mentioned above, it's already in the developers TODO.
I'll coment your BA thread with a possible solution.
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Hey again,
Is there a problem with the set Alpha node then? this node does not seem to work either...
The way i am currently overriding it is by using the alpha socket on the composite node... this seems to work fine.
Cheers for following it up
Carlo
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Carlo: Please disregard my previous comment. When I replied I didn't see your screenshot and when I rendered without baking the cloth in 2.63a it looked right (or maybe I overlooked the preview during render).
Now that I saw the screenshot and could reproduce the problem I can confirm it's something completely different, and it's a bug.
Blender is indeed showing a weird alpha when rendering, and that weird alpha is saved when you export animations, no matter what you do.
It looks as if the operations in your node tree create a weird alpha value that survives all the compositing and can't be overriden by any of the alpha setting operations available.
Sorry for the noise. I misjudged your report.
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The issue here is that somehow there's a connection to Alpha socket of Composite node. If you'll remove this connection by dragging it off deom socket or deleting node and adding it again -- everything would be fine with alpha.
The question is -- how you managed to run into such a configuration and are you able to reproduce it again? If it's not reproduceable we can't fix original issue..
Lukas, maybe you've got some clues here (maybe something to do with copy-paste or maybe it was fixed already)?
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The compositor node in the file has something attached to the alpha channel. if you remove this (just click on the Alpha socket of the compositor node) you will see that everything works fine.
Closing the bug for now.
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Hey All,
I cant remember how I did it, I didnt realise that the composite node had a stray connection into the alpha. If I come across this problem again i will reopen / submit a bug request with the procedure.
Thanks for your time!