noisy multimatte

[klex167]

I try to calculate a clean multimatte in the render elements but in transparent objects the matte is very noisy. Probably its not calculated by the denoiser.
Is there a way to get the noise out of the multimatte without increasing up the quality too much? My threshold is 0.05 and I want to avoid to long rendering times.

Testscene is attached.

[aleksandar.kasabov]

Hello klex167,

The MultiMatte render element is not denoised by the denoiser and in order to reduce the noise you will need to increase the render quality.

[klex167]

Thanks for the reply. That is sad because now the denoiser makes no sense for me. And the rendering time will increase enormously. Why was it so easy with Vray 3.7 to get clear alpha maps?

This is an old alpha map of 3.7 (just clear grey values):

[aleksandar.kasabov]

Hello,

Please note that the Alpha channel is denoised by the denoiser but the MultiMatte render element isn't. If you wish to use the alpha channel, simply disable the "Affect Alpha" in the "Options" tab of your dome light. I hope this helps.

[klex167]

Thanks Aleksandar. I will check this out.
Best - klex

[klex167]

Hi Aleksandar, I'm not sure if I'm understanding it correctly.
I disabled the "affect alpha" option and added the "object select" to the render elements. For the object select I get an alpha map with a noisy output again. See picture:



With "alpha channel" you mean the object select output?

[aleksandar.kasabov]

Hello klex167,

The "Object Select" render element gets denoised by the denoiser if the option is enabled. However, in my previous post, I was referring to the alpha channel which also gets denoised and you can use it instead of the MultiMatte channel. Please check the following screenshot.

[klex167]

Hi Aleksandar,
now I understand what you meant with alpha channel. I found it in the VFB.
But how can I render and save it? Do I have to activate it somewhere? I'm rendering animations with lots of frames.

And what if I have other objects in the background? It won't work right?

[aleksandar.kasabov]

Hi klex167,

But how can I render and save it? Do I have to activate it somewhere? I'm rendering animations with lots of frames.

If you are using the V-Ray Output system and saving multichannel files (such as .exr or .vrimg) the alpha will be saved as one of the channels. If you are saving single-channel images you will need to enable the "Alpha Channel to Separate file" in the settings. If you are using the native C4D save system you will need to enable the "Alpha Channel" option.

And what if I have other objects in the background? It won't work right?

If you have another object in the background, you can add an "Object Properties" tag to it and then set the "Alpha Contribution" to 0 or -1. Please check this video. I hope this is of help.