Background Color During Rendering

[NurbNerd]

How do I change the background color in an animation sequence? IThe default is blue. I woud prefer "clear" or green. I'm planning to merge the animation with another video.
Thanks.

[delic]

set the render to"premul" instead of "sky" option in the render settings.

[NurbNerd]

Originally Posted by delic set the render to"premul" instead of "sky" option in the render settings.

Thanks. "premul" appears to turn the backgound black. How do you change it to clear or another color?

[delic]

you dont need any color if you want composite the render, just save it in png, tga or tiff sequence with RGBA, so you'll have an alpha mask ...

[delic]

set the render to show in image editor instead of render window in the Output dialog box, so you you can see the alpha channel by clicking on the two buttons right of the lock in the image editor .

[NurbNerd]

Originally Posted by delic set the render to show in image editor instead of render window in the Output dialog box, so you you can see the alpha channel by clicking on the two buttons right of the lock in the image editor .

Is this if you are doing the composition in Blender directly?

I'm doing the composition in another program (Sony Vegas). The background of the rendered animation is not "clear" so I can't lay the rendered track on top of the video. I need to setup a "Green Screen" Chroma Key, therefore making the background of the render green. Is there a way to do that? I'm new to this, so I may not be explaining things correctly....
Thanks,

[Marcion]

What a Chroma key does is make a certain color transparent. But it almost always does this a little poorly. What Blender can do is within the render itself make those areas transparent. That is the "alpha" channel. delic was explaining how to get an alpha channel. To do that follow his instructions, with the keys being not rendernig the background, rendering the animation to png (has alpha/transparency channel) and rendering in RGBA (Red, Green, Blue, Alpha). And yes, this image sequence will have the background transparent in any editor you put it in.

[NurbNerd]

Ok, I get it now.
The main point is that to get an "alpha" channel you must render with RGBA. I was able to get the alpha channel when rendering to .AVI RAW format. I then brought that clip into Sony Vegas and put it together with the main video and rendered out to the final shot.
Thanks for your help guys.