CGTalk - Alpha gain technique....

View Full Version : Alpha gain technique....

Andrei2k

01-26-2003, 08:13 AM

I've need to composite (using a shadow render pass over footage) to make my composite of maya and footage to seem more real. When i render the shadow pass the alpha channel is all white meaning my shadow is black in after effects. I don't want to use opacity and layer efects in AFX because it doesnt look right so I hear the alpha gain is what i need to modify......my question is how can i connect the alpha gain to a value of the shadow i need without just wingin it and picking numbers and rendering trying then picking other numbers rendering , trying, etc........i know im getting into stuff a little over my head.
THanks in advance. :applause:

mattwood

01-26-2003, 11:01 AM

I think you've been misinformed. Adjusting the alpha gain in Maya would only give you the same effect as adjusting the layer opacity in After Effects. So you might as well do it in After Effects.

JoeSchmo

01-26-2003, 11:56 AM

you could use a background shader instead...
Joe

Andrei2k

01-26-2003, 05:16 PM

I heard about using a background shader but I'm not sure of the technique. I you can explain it a little Joe I will definitely give it a try. Thank you.

JoeSchmo

01-27-2003, 11:12 AM

basically you assign a 'use BG shader'
to the ground where your 3d objects shadow
is gonna fall....
if the 3d object's shadow is gonna fall on another object
(in your footage),
you might want to model a simple version of it,
just getting the basic shape of the object that the
shadow is gonna fall on, and assign a BG shader to that too.

then you can set your lights shadows in Maya how you like 'em
when you bring it into AFX, only the object and its shadow
( with partial transparancy ) will come in. Also the shadow will
bend around the simple object you modeled.
Look for some tutorials and read the help files...
It's really cool.
Joe

CGTalk Moderation

01-14-2006, 06:00 AM

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.