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View Full Version : image planes in V-Ray?

cgbeige
10-30-2010, 10:28 PM
I'm trying to find a good way of doing image planes with V-Ray for rendering something on a background within Maya but the Maya ones are very slow to render. I tried changing the Background attributes in the V-Ray environment settings but there's no way to get it to fit to my resolution gate. I've figured out how to make a simple sprite constrained to my camera and put a V-Ray mat on that but I can't find any way of having that simply render to match the image, with no GI/shadows, etc.
cgbeige
10-31-2010, 01:07 AM
ok - I found a weird workaround that shows up correctly, regardless of camera exposure settings, but you'll need to worry about linear workflow and keeping gamma at 1.0.

Make a plane, aim constrain it to the camera, move it well away from your objects and size it to the resolution gate. Then apply a V-Ray Light Material to it and enable "Compensate Camera Exposure". Then turn off everything the plane's render stats except primary visibility.

It's not terribly efficient, since it's sampling it like geometry, but it's accurate (image deleted because I fear the wrath of Corbis lawyers.)

Now to figure out a way to get a "use background" shader with shadows for the base plane. My life would be a lot easier if the V-Ray Blend Mat had a multiply mode. I guess I'll just use the Material Wrapper method for the final and do the comp in Photoshop or Nuke.
jasonhuang1115
10-31-2010, 02:43 AM
I wondered the same thing of why Vray rendered the image plane so slow. Is it because its a pure raytracer with no scanline mode?
cgbeige
10-31-2010, 05:14 AM
heh - I just got your email about the passes thing and then checked this thread.

Since the image plane is actually an object, I think V-Ray does a sort of quick and dirty conversion of the surface shader which is badly optimized, so it takes a long time to render. That's just a guess.
thev
10-31-2010, 03:37 PM
I would say it's because, from the point of view of V-Ray, the image plane is just another object, so V-Ray will try to antialias it like everything else, even though it may not make much sense. You can use the V-Ray sample rate render element (or the "Show samples" option for the image sampler) to see if this is the case.

Best regards,
Vlado
cgbeige
10-31-2010, 05:57 PM
Is there a way to individually control object samples, like with RenderMan?
thev
11-01-2010, 09:23 AM
Nope, at this time it is not possible, although it is in the pipeline down the road...

Best regards,
Vlado
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