Vray multimatte in 3ds max

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  01 January 2013
Vray multimatte in 3ds max


I've already ask this question in the compositing section. But maybe there are more users here who can provide a solution or a workaround.

I'm rendering a scene and would like to use the multimatte pass on several objects.
The problem is that this scene is very dark.
Somehow Vray doesn't render a clean multimatte pass in the darker areas.

In the attachment you can see a testscene.

On the left side you can see the multimatte when the only light in the scene is turned off or it's intensity was set to a low value. Have a look at the edges where the objects are overlapping each other.

On the right side the VrayLight was turned on and the multimatte pass looks okay.

What am i doing wrong? Is there a solution for it?

of course i can render one time with the right light intensity and one time with a brighter scene get the right multimatte. But in the current job I'm rendering a animation with many frames and i don't want to render the whole animation two times.

Is there a work around?
Attached Images
File Type: jpg Multimatte.jpg (87.5 KB, 39 views)
  01 January 2013
I believe this is completely dependent upon the sampler you're using, darker areas having less samples, thus looks grainier. The solution may be to up your samples. What sampler are you using? To determine if this is indeed the problem, used fixed sampler and see if all edges appear the same.
Chris L. Harkins
  01 January 2013
IIRC, most of the RE inherit the sampling from the scene image sampler. So in the case of a dark scene the sampler will complete sooner. So to get better sampling in your multimatte you will need to up the sampling for the image as a whole. If you are using DMC up your Min samples and/or lower your noise threshold to push more samples to the scene and the RE.

"The Evil Monkey hiding in your closet."
  01 January 2013
I know it's slightly off topic, but may help you out, but have you seen this script I put together

Effect ID Changer

It helps automate and organise multimatte elements when rendering.

  01 January 2013
Hi and thanks for the support.

I'm using the Adaptive DMC Sampler for my renderings.
'll do a test with the fixed Sampler and see who the multimatte will look like.

So if i want to use the DMC Sampler i have to increase the min Samples of the adaptive DMC Sampler and decrease the threshold. What about the adaptive amount then?
This solution would increase my rendertime a lot wouldn't it?.
Maybe its better than rendering 2 times

The scene consist of a dark theater hall were you can slightly see the contours of the heads from the audience which were lighted by a rim light. Increasing the min samples and decreasing the threshold means that vray will shoot much more samples everywhere even in areas which are just black in the beauty pass right?

Is there maybe another way? I mean the beauty pass already looks good. It's just the multimatte pass.

@DeanPunchard That tool looks useful. I'll give it a try. Thanks
  01 January 2013

This is a small trick that shouldn't affect rendertime too much, and should provide clean multimattes:

Create a VRayExtraTex render element, and assign a falloff map to it. Usually I have to change the falloff type to 'fresnel'. This makes sure that the edges of objects get enough samples for clean multimattes. If you are still getting jaggy multimattes, try assigning small noisemaps to the falloff colors.
TD / 3D Artist at Brink Helsinki

Last edited by ebee : 01 January 2013 at 01:56 PM.
  01 January 2013
That is it!

Thanks a lot.
  01 January 2013
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