Motion Blur and Alpha

[yogiparish]

Hi,

I am not sure, where I am doing this wrong.

I want to render out an animated scene with motion blur and compose it onto another render.
But I don't seem to get a clean alpha, but an ugly white fringe.

In the octane settings I have checked: alphachannel
keepenvironment on or off doesn't make a difference.

And in the regular "save" options of C4d I use Alpha Channel and Straight Alpha.

The scene has no objects or sky in the background.

Any tips?

Thanks a lot!
yp

[aoktar]

Hi,
check also prem. alpha.

[yogiparish]

Hi,

thanks for your answer. I guess you mean the premultiply alpha button under the "Camera Imager" tab in Settings?
That didn't help either

I've attached two screen-grabs

If anybody has a file of a simple setup with working alpha and motionblur for After Effects import it would be greatly appreciated. I am a bit confused by all those different alpha settings, I have the feeling that I missed one important button somewhere...

thx
yp

[atome451]

In the regular "Save" options, check only Alpha channel. Not Straight alpha.
Test the premultiplied alpha if the result isn't good enough like this.

Keep environment makes big difference with blur, matte, etc, on colored environment. You'll see the colored environment in the blur and the matte.

EDIT: for me the result if better without premultiplied alpha. But you'll see the real result in visualizer only in alpha channel, the color channel create curious but correct things once combined with alpha channel.