Volumes do not appear when transparent film is enabled #42755
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Reference: blender/blender#42755
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System Information
Archlinux
Blender Version
Broken: 2.72b (
9e963ae
)Short description of error
Volumes do not appear in the final combined pass when transparent film is enabled and the image is rendered with F12. They do appear in the various other passes though (e.g. emit).
It works as expected in viewport render.
Unrelated: also, there is a strange firefly which is visible in camera view+viewport render regardless of the number of samples. As the object is only rendered with an emission shader, this doesn't seem right..
![examp369.png](https://archive.blender.org/developer/F127669/examp369.png)
Exact steps for others to reproduce the error
Changed status to: 'Open'
Added subscriber: @gandalf3
Added subscriber: @mont29
IIrc, this is expected result (a matter of premultiplied vs straight alpha…). Sergey should know for sure! :)
Changed status from 'Open' to: 'Archived'
Yes, this is exactly a difference in handling premultiplied alpha in the viewport and image editor. This is a known behavior which i'm trying to address for 2.73 release. It's a bit tricky tho, because in viewport image is for sure properly premultiplied, without any possible precision issues caused by compositor, which make it really easy to mess things up in the image editor.
Anyway, there are some more changes to be done to the way how the alpha is handled in the image editor, would address them all together.
Added subscriber: @blackdot
hi. has this issue been resolved, or can it be worked around somehow? i stumbled upon it today and found this report by websearching the problem. i'm using 2.74 (also tried the latest build for today). left is viewport rendered, and right f12 rendered.
although the volumes (in my case those cylinders) can bee seen in various passes, they dont seem to be recognized by the "alpha". regards
Added subscriber: @alexdemulder
I'm still getting this bug in 2.75, I believe it was gone in 2.74 but I'd have to check. Should this be fixed? If so I'd happily share my scene.
AFAIK this has yet to be fixed (if it was gone in 2.74, thats odd..), as it's caused by fundamental differences in alpha handling (as Sergey explained).
Added subscriber: @edisto
http://blender.stackexchange.com/questions/32900/how-to-properly-render-smoke-on-a-transparent-background
Attempt 1 works very good as a workaround.