Black outlines when exporting images


I’m getting these black outlines on any exported image channel as if the application is just masking the rendered window with its black background. How can I get rid of these?

Premuliplied alpha can cause this. Another workaround, which is probably the best and most commont solution, is to change the render background color to grey to match the smoke:

Thanks, I’m assuming this is the only setting to set the alpha?

I’ll give that a shot with the grey background but then it will create whiter outlines for the shadows especially while rendering direct lighting. Is there no other solution to render images with transparent background?

It shouldn’t create white outlines if you match the colors. If you see that, post a screenshot. Straight Alpha is a bit bugged right now too so that could affect things.