CGTalk - Backgrounds/Skydomes and alpha channels

View Full Version : Backgrounds/Skydomes and alpha channels

Jon_Pran

11-30-2002, 08:26 PM

I am trying to render a sequence of images with a skydome as the background. I need to be able to cut out the object in the middle, which is partially transparent, with an alpha channel (not much time and a ton of images). I tried using just the normal environment bg, but it renders the object as though it were on a black background (you cannot see the sky through the object).
Is there a way to include the bg environment in the transparent object (this would keep the alpha channel that is made)
OR
Is there a way to generate an alpha channel for the object if I were to render it with the skydome?
Any help or suggestions would be appreciated. It would seem as though I am missing something?

ilasolomon

11-30-2002, 09:45 PM

would you show a sample of what you plane to do?

Jon_Pran

12-01-2002, 02:17 PM

I am basically trying to create frames of an animation, but I just want the object (to be able to cut out in Photoshop) and not the entire sky. I could do this manually, but it'd take forever.
Here are 3 images of what I need. I made a cube that the camera rotates around and I want to be able to render them with the sky (you can see it through the cube) in the bg. I'd like to be able to use an alpha channel to cut it out, if possible.
That scene has a cube, skydome, camera and ground plane.
Thanks.

http://photos.yahoo.com/bc/design7712/lst?.dir=/Transparency

12-01-2002, 02:45 PM

You could render the sequence normally (with the Skydome in ..etc), then re-render it with the elements you do not want in the Alpha channel (i.e: the skydome) set to 'non-renderable' (right click, properties, renderable check box). That way you'll have one sequence of the diffuse colour, and a seperate sequence to be used as a mask?

Does this make sense? (Or is it even what you were after!)

Jon_Pran

12-01-2002, 02:59 PM

Yes, thanks, that does make sense. I was hoping for a quick fix, though. Project has to be sent out tomorrow morning and I am making a large collage, so I'll probably just render them out with an alpha channel and forget the sky. Good suggestion, I'll probably end up using it on a later project.

CGTalk Moderation

01-13-2006, 11:00 PM

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.