[Bf-committers] Is alpha within Blender totally broken?

[Mats Holmberg]

You are on the right tracks, Troy. The alpha issue is something we've been pondering about at Studio Lumikuu also. If you composite within Blender there really are no issues, but, in my case, using After Effects gives very weird results.

I've always used premultiplied png -files before, as nothing else ever seemed to work, but from feedback I understood that this is plain wrong (the results were fine though, which tells me that Blender does it wrong). Anyways, I'm not able to look into this at the moment and produce any examples - I could check and report my results tomorrow. But just to let you know, I agree completely that there is something _seriously_ wrong about how Blender handles alpha channels.

Cheers,
-mats

On 17.7.2011, at 6.06, Reuben Martin wrote:

> On Saturday, July 16, 2011 02:37:57 PM Troy Sobotka wrote:
>> So far, I've been experimenting with several files and uptake tools
>> using Blender in conjunction with Nuke. I have yet to be able to find
>> a pattern that delivers proper alpha channels.Perhaps someone here can
>> shed some light on the matter.
> 
> I can't speak for Nuke, but if blender has a bug concerning alpha channels when rendering, then it also has the same bug in the compositer, because I've never had issues keying anything.
> 
> The first two images look like what happens when trying to key a pre-multiplied image with a white background that isn't properly removing the matte. The second two look like trying to 
> key with the matte being removed, but not useing linear color space blending in the compositing. But I don't know what your actual settings are.
> 
> Straight-keyed Alpha, CM on, rendered to Half-Exr, Composited with CM on. (in blender) http://img692.imageshack.us/img692/779/compositescreencap.png
> 
> -Reuben
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