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View Full Version : No graded transparency in alpha?

Tr4uma
01-05-2009, 04:04 PM
Hi thanks for looking...

Im rending out an animation sequence and intend to composite in the background. There is a plane with a mid level transparency value in the scene but the alpha i get out is completely solid. I need the transparency to be represented in the alpha as well so when i composite, the background shows through slightly.

heres an example image:

http://img101.imageshack.us/img101/7039/imageuy9.th.jpg (http://img101.imageshack.us/my.php?image=imageuy9.jpg)

and the alpha i get:

http://img253.imageshack.us/img253/4271/alphabz3.th.jpg (http://img253.imageshack.us/my.php?image=alphabz3.jpg)

so hopefully you can see the problem with the "miracle windows" plane. i found some forums with solutions for this when using mental ray...but im using the maya software renderer so thats no good.

Hopefully this is just a matter of turning a few render options on, so any advice would be much appreciated. Thanks
Tr4uma
01-08-2009, 01:53 PM
if anyone has any tips at all that would be most appreciated
jeremybirn
01-08-2009, 03:57 PM
First, use a black background. Take out whatever is white there to avoid trouble.

There also might be a problem with whatever shader you're using not outputting the transparent alpha. You could try replacing it with a Surface Shader with a light gray Out Matte Opacity.

-jeremy
Tr4uma
01-08-2009, 06:28 PM
yeh the white BG was there just to help it show up better. its not in the alpha tests. Also, the surface shader wont work as i need the guys legs or whatever is behind the transparent thing to go fully white as that's animated and needs to be solid.

thanks though :)

i could assign a complete white shader to everything in the scene and do a normal render with a black background and that should work...but its just i want to avoid having to set all 50+ of my scenes up and re-render when there should be a way to just get the correct alpha channel in the first place :(