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dr_bob
03-18-2003, 04:41 PM
Hi All

I've created a (hardware rendered) particle effect using sprites, which I want to combine with footage of a semi transparent (software rendered) object, and I was wondering if anyone out there could offer some advice on the best way to composIte them (in After Effects 5.5). The problem is exacerbated since the particles have to appear to be *emanating* from the object (ie they are created inside the object and flow outwards).

I'm guessing rendering with z-depth activated would be the best method, but I've found the documentation a little sketchy. If you could offer any suggestions it would be greatly appreciated.




Best wishes,



Steve
lostpencil
03-21-2003, 04:36 AM
Hey Steve,

Fun problem. Here is what I'd do, I think... (maybe not the best way, but I think it will work). The object that is partially transparent in my example is, say, a pipe. The particle stream is your hardware render of particles that are coming out of the partially transparent pipe. Render out the particles without the pipe in the picture and render out the pipe without the particles in it. Then in After Effects create three layers (with 1 being the top).

1) pipe (with mask) - with blend mode
2) particle stream
3) pipe (with inverse mask)

What I mean in layer 1 by "With mask - with blend mode" is the image of the pipe has a mask on it which only shows the part of the pipe that will contain the particles inside the pipe. Everything else of the pipe will be masked out. The 'With blend mode' indicates that I blend that layer with the lower layers in such a way so that it looks like anything underneath this piece of pipe is behind the pipe. Go through a few blend modes and see which one looks best - maybe lighten or overlay mode.

Layer 3 "with inverse mask" is the image of the pipe that has a mask that shows the part of the pipe that doesn't contain the transparent part and the part which the particles pass in front of....

Essentially, in this scenario, you sandwich the particle stream between two parts of the pipe. This may or may not be the solution for you, but maybe the idea will get you headed in the right direction.
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