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Smoke Alpha Channel

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Can anyone shed light on how to get a good alpha channel on smoke rendering?

Attached is a set of images showing what we mean. All the images are 32 bit Tiffs with samples set to 24.  

We're getting some dark edges on the side of the alpha channel. Attached is an image showing what i mean. 

We've tried changing the alpha channel from normal to straight which makes the smoke render a lighter colour and changes the dark edge to a light edge. 

Any help much appreciated!!






CyclesPhone+VFX_Still Alpha test 2 (0-00-00-00).jpg

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If you're using After Effects to view your renders, you can go to "Interpret Footage" and set the alpha to "Premultiplied - Matted With Color" to black, which will be the default for C4D renders. Otherwise, your straight alpha render is how the smoke looks against that lighter background if the alpha interpretation is set to "Straight - Unmatted"

If you're finding the smoke still doesn't look "right", it might be worth checking your renders against a similar colour background to the one you'll be compositing against, and dial in the look you want with different lighting and/or smoke colours or density. Or you can get more advanced and render a smoke pass as a separate render with a "holdout" shader applied to the non-smoke objects, then you can lighten or darken or even recolour the smoke in post as you see fit. Obviously render out your objects with no smoke as a separate pass too

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