How to isolate fire with alpha?

[Zakkorn]

As you read on the title, how can I isolate a fire from an image to process later?
I render in png with alpha but in alpha I get only the objects sources of the fire.

There is no fire at all.

I render with VrayAtmosphere as an element and still a similar result. The fire is only front of the source objects and where is no object there is no fire as well.



Stupid question I know but I have no idea what else to do

[Ivaylo Katev]

by default the fire rendering mode is "fully opaque" (the name is a bit misleading, perhaps we have to reconsider it) , change it to some other, "use smoke opacity" or "use own opacity"
the first one is the physically correct mode, but is harder to manage, because it locks the smoke and the fire alpha.

[Zakkorn]

You mean there is no way to isolate fire and post process it?

[Svetlin.Nikolov]

There is a way - you have to switch to "Use Own Opacity" mode, raise the fire multiplier to about 8-10, and drop the opacity multiplier to about 0.05-0.1 - this will get you close to the look you had before and you will also have alpha (it depends very much on your setup what the actual values should be, but using these two controls you will be able to replicate your result from the "fully opaque" mode).

The "Fully Opaque" mode replicates nature's way of fire - it has color, but it doesn't have alpha. You could get alpha with the "Use smoke opacity" mode, but you will have to simulate again if you don't have a smoke channel and it will generally complicate things more.