composting smoke trail?

#1

I am trying to create a rocket trail using Combustion’s particle operator. The problem that I am running into is that it is not a clean composite. A soft black border is surrounding the smoke making it look pretty fake. I created a composite in Combustion and brought my background file into one layer and put the particle operator onto that. I am pretty new to combustion, never used it for particles before so I didn’t know if this was common or if there is some way around this. I attached a pic below of a test frame to kind of get the idea of what I am running into. If any one could help I would greatly appreciate it. I am using Combustion 2.0 on a mac OSX. Thanks for any help.
Ryan

#2

Look into the mode with which Combustion is interpreting the alpha channel for that layer and those particle sprites. It should be Pre-Multiplied. I’ve never had a problem with the particle-op and the alpha mode so I’m not sure that it’s even an issue. You might also try changing the compositing mode for the particle-op to be Add or Screen. Add will drop out any black in the layer you’re comping on top, since black pixels do not add any value to a shot.

As a side note, you said it looks unrealistic, but you’re not likely to get very realistic results with the shot you have set up there. If the rocket is supposed to be coming from the characters in the background there, then there is a move in the Z-axis, which 2D particles cannot replicate properly. What you could try to do would be to warp the size of the particles so that they’re smaller as they are near the character and grow in size as they approach the camera (basic perspective rules). But that’s just assuming that was your goal in the first place.

#3

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