Comping 2D particles properly

[robtheg]

Hi all. I did several smoke particles with Combustion but don't look right because always have a dark edge and I tried to color correct, but the dark edge is always there. I tried all kind of comp tricks but doesn't look right. How can I get a photorealistic smoke with the Combustion particles?

Thank's.

[dlm]

Hi,

Put your particles onto transparent layers and use the SCREEN transfer mode in the layer composite options. This should get rid of the black edges.

Hope this helps.

Regards
Grant

DISCREET EMEA

[robtheg]

Yes, this is a good option but I don't want to use screen because the bright changes over darker objects, and looks different to my render.
I tried different options and, by far, the best option to keep the particles close to the original look is to render the particles over a black frame (solid, not transparent) without alpha and comp this result using luma key and cc. The edges disappear and you have a nice control over the result.

Thank's.

[robtheg]

Thank's, I tried all your solutions but the problem remains. If I apply a particle operator to one layer in Combustion and I design, track and comp that particle INSIDE the particle operator, everyting works fine and the look is right. But if I render only that particle and I try to comp this new layer as an individual layer with his own alpha, never looks the same.

Thank's.

[joojaa]

There are 2 kiinds of alpha.

Premultiplied wich is the defuault in videolike media work. (thsis is probably a historiccal fact form times when every processing time counted, but its not less precice than straight just different)

And straight wich is for instace what photoshop uses.

MOST comp apps have a option to work with either or theese modes. Consult your manual on alpha interpretation and changings the settings for it.

And yes even photoshop can do it its under the defringe menu off sellections. Just as a example.

[george-stankevich]

Yeah I've had probs comping particles in Comb too.

You can either pull a luma-key off your particle layer and use that as the alpha, or use Additive mixing instead of Normal.

Or as Joojaa said, use pre-multiplied renders.

[marcosissler]

Actually - it may be "Premutiply ON" that is causing the problem.

If you render out with Premutiply ON - your FILL will be keyed over your background (black - I'm guessing!) Then when you go to key it over something else, the edges (and the black) will layered over the BG, hence black edges.

Turn Premutiply OFF, and see if the edges don't go away...

Also, never use premult when you are exporting matte and fill for other programs to use.

Good luck,

Kim