rendering background
 

i was just wondering if its possible to render out a transparent background in maya for later compositing (so that u dont hav to rotoscope/key out colors)

save as a file format, like TIF, that includes the alpha information and use the alpha to key on.. voila.

Yep, saving as targa is great :).

thats in render globals btw, you just include the alpha information as well as colour

ok, i saved the image as a tif. I go into photo shot. I can turn on and off the alpha layer in teh channels area of Photoshop, but how can i put an image back there??

CTRL+click on the alpha to select your bg area.
OR
Select your alpha, and go to SELECT > LOAD SELECTION.

Iether way, you should now have a selection that you can use to place your bg into.

NOTE: Depending on your alpha preferences from another app, you might have to iether INVERT your selection, or INVERT your alpha to get the right selection:)

yeah, i got that the first 3 seconds. But when doing it with a sphere, there is still a black line around the sphere. Is that just a long shadow?

SWEET! ok. the black line is just because of the shape. Also. Something that is partly transparent, is partly transparent in photoshop. COOL!

I've noticed that too when I render out images with an alpha. When I open it in photoship, there's a thin black stroke around where the alpha meets the image. Anyone know the reason for this? I've sort of gotten around it by loading the image and just contracting it 1 pixel, inverting the selection and deleting. Still, I'd like to know how to prevent this from the source. Any ideas?

instead of contracting it by 1, try feathering it by two.

I think Photoshop dopesn't pre-mutilply the image. In After Effects when I leave off pre-multiply, I get the thin black outline. When I turn on pre-multiply, the black line goes away.

BTW, where do you set the BG color for renders? I've looked all though the Render Globals and I can't find it.

-dann

Dann: Go to the attribute editor for the camera you're rendering from and choose the environment tab. This will allow you to change the background for you renders.

UG: I'm not a big fan of feathering for the most part because it washes out (blurs) the objects edges (something I definitely don't want). I'm more concerned with figuring out where the black line is coming from so I can remove it properly.

Interesting about the Pre-multiply, Dann.