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Old 09-19-2012, 12:07 PM   #1
Mr Whippy
Graphics and stuff
Join Date: Mar 2003
Posts: 174
Renderer filtering issue

I'm getting a halo when compositing my EXR footage (or any footage for that matter) with my video footage.

I can get around that by rendering a mask pass with the Max scanline "Plate Match" anti-aliasing filter which is almost totally perfect.

But it's just annoying, especially if I want to use motion blur from within something like Mental Ray rather than doing it in post.

Does anyone know the 'right' setting to get Mental Ray to draw alpha that is comparable to the "Plate Match" Max AA filter?

Thanks for any advice


Last edited by Mr Whippy : 09-19-2012 at 12:15 PM.
Old 09-19-2012, 03:50 PM   #2
Mr Whippy
Graphics and stuff
Join Date: Mar 2003
Posts: 174
Oh, I think this makes sense now.

I've just put a huge plane in the background of my scene with the MR matte/shadow/reflect material on it and the MR filtering now looks much better for compositing use.

Is that all there is to it?

Any elegant ways to avoid having to make that geometry? Ie, a toggle box somewhere that just runs basic matte AA filtering?

Is motion blur gonna break if I have a plane on the camera back plane face with the MR msr material that moves around with the camera?


Old 09-19-2012, 03:54 PM   #3
On the run!
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Graphic designer extraordinaire
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Posts: 4,497
Im not sure what you mean... Do you mean you are getting a fine border around your alpha channel? If so, try using premultiplied alpha
Old 09-19-2012, 04:10 PM   #4
Mr Whippy
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If I use EXR (or any HDR/LDR format) I get the outline with both pre-calc and post-calc alpha.

It just seems the filtering will only work in MR with the matte matterial in the background, but that costs rendering speed, so right now I'm just running a flat plane behind the object linked to my camera.

Will do some more testing to assure it's running ok. Not sure if the moving back plane will cause motion blur problems but I guess I'll find out soon


OK, think it's ok now. I just need to turn motion blur to "by object" in the render dialog, then enable it only for the required bits in the object properties dialog.

If I keep the moving back plane without motion blur it renders much quicker now.

All good!

Last edited by Mr Whippy : 09-19-2012 at 04:37 PM.
Old 09-19-2012, 04:34 PM   #5
J. Schreyer
ARRI Berlin
Berlin, Germany
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Can you post a picture of your problem?
Old 09-19-2012, 04:46 PM   #6
Mr Whippy
Graphics and stuff
Join Date: Mar 2003
Posts: 174

Basically I want to render with AA filtering to background that doesn't leave a halo.

Mental Ray only has one way to achieve that it seems (ie, no toggle like scanline render has), and that is via the MR material matte/shadow/reflection, even though I only need the matte bit, and not for anything other than activating the appropriate filter for edge > background AA filtering that doesn't cause a halo.

Sooo, I put a plane in my scene and apply the appropriate material but a big plane hits render speed across the empty areas of the render (not so bad but it's just not required)

So now I've put a small plane behind the subject and just track it behind it through the camera move.

However you just need to make sure you switch off global motion blur and enable it only for your subject.

So it's working nicely now.

Bit of a hassle vs Max scanline where you just select R2/matte plate from a drop-down menu but I've got there in the end

Just testing the process for now to make sure it works as intended as I did a project 4 months ago and was doing my masks in scanline but obviously this is a better way it's just a hassle to set up initially
At least I can leave MR to do the lovely motion blur it does now!

Thanks for the help so far!

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Old 09-19-2012, 04:46 PM   #7
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