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PolyMangler
02-18-2003, 03:14 PM
hey guys this would be my first time droppin a thread in here and what better way to herald my arrival then with a simple question that's been bugging me.......

How do i get LW to make an alpha for a volumetric light?

I've been stuck on this all day and the manual doesn't seem to say anything about it

btw great community everyone, this place just became my new Home :buttrock:

policarpo
02-18-2003, 03:27 PM
perhaps Unmult will do what you need it to do?

http://www.ats-3d.com/#Image Filter Plugins

PolyMangler
02-18-2003, 05:06 PM
Muchos Gracious for the link Policarpo. Post Alpha is just what I was looking for.

Although it's kinda dissapointing seeing LW need a pulg in for something like that, seems like it should be in the box.

Dah well, i'm not complaining still makes for a bad arse program and i'd rather plug something like that in then a renderer *cackles*

CourtJester
02-18-2003, 05:34 PM
I just did a test with Opacity >0 on a volumetric light and got an alpha... am I missing something?

The alpha doesn't reflect shadows, however, raytraced or shadowmap.

Unmult sounds like one of the solutions for compositing lens flares, but I figured out how to do that in AfterEffects:

1. Render your layer with the flares in it.
2. Import this layer into your AfterEffects project.
3. Of course, no flares except on top of the opaque geometry. No problem! Re-import the same layer, Interpret Footage, then invert its alpha AND set its premultiply color to White (assuming a premult to Black background)
4. Add the new layer right underneath the previous one, and set the blending mode to Add. And there you are.

This will also work for volumetric lights that have no opacity.

If anybody knows how to invert the alpha and set the premult color at the Composition level instead so I don't have to re-import and re-interpret the same sequence, I'd like to know.

Rendering the flares/volumes in a separate layer is still better if you need the control in post.

RuiFeliciano
02-18-2003, 06:01 PM
CourtJester,

unless I'm misunderstanding you, if you're using LW 7.5 you now have the option of having lens flares included on the Alpha channel so compositing is easier.

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