View Full Version : Volumetric Lights and Compositing

03-29-2004, 12:23 PM

I'm working on a scene that uses a volumetric light, like a searchlight through fog. I want to be able to render the animation once and the have the option of dropping in different backgrounds (the client wants to use the same searchlight with different promos). However, when I bring the sequence into AE only the portion of the volumetric light that was rendered with a surface somewhere behind it shows up. Areas of the light with no other object behind it are lost. Is there a way to render volumetric light effects to be used in compositing? I could re-render with each different background, but with the resolution and AA settings it takes a long time. It would be nice to just have the one rendered sequence and be able to drop in whatever background we need.



PS: It appears there is no alpha or matte info...

03-29-2004, 12:29 PM
render vol light on black background
then you can compose it on background with after effects with vol light layer setup in multiply or screen mode.
have a nice day.

03-29-2004, 12:52 PM
That got it pretty close. Unless I did it wrong. It washed out the geometry that I had in my scene. So I fixed that by adding the layer twice, the first imported as Straight and mode set to Normal. The second imported as Ignore and mode set to Overlay. It seems to work pretty well. The other option is to render the volumetric light with no geometry and render the geometry with no vol light as two separate passes. The only issue there is the light comes from behind some cut outs of geometry. I tried setting the geometry to Unseen By Camera for the light pass, but the light no longer gets shaped by the geometry. Is there a way to get around this?


03-29-2004, 01:01 PM
yes, leave your objects on but check "matte object" That will turn your object completely black and I think add it to the alpha channel. The button is on the same panel as "unseen by rays"

03-29-2004, 02:12 PM
BINGO! Perfect, excellent, thank you, thank you all!!!