Matte Shadow quality problem

[simmsimaging]

I've had a lot of problems with using the Matte Shadow Render Element - it often generates a lot of artifacts/noise (see image below for the most recent example). The beauty pass looks fine, it's just the MS pass that shows up this way. Is this normal? I searched around the forum but could not find any threads on it, so I figure it's just something I'm doing.

Does anyone have any idea what settings I should be looking into?

b

[vlado]

This probably happens in areas that are relatively uniform in the RGB channel and so they don't have too many samples.

Best regards,
Vlado

[simmsimaging]

So how would I go about getting a cleaner shadow pass for compositing on a different background?

Thanks Vlado
b

[simmsimaging]

I found that switching the background plane from matte object to normal helped clean up the noise somewhat, but it doesn't give me the same matte shadow pass, which introduces different issues. (see image)

That might still work, but there are definitely other areas of low sampling that create problem spots. Would there be another way to do the shadows for comping?

[vlado]

You could use the alpha generated from matte objects; since the alpha is included for AA, the shadows there should be better.

Best regards,
Vlado

[simmsimaging]

I'm sorry, I don't really understand what you mean by that?


b

[vlado]

If you turn on the "matte" option of an object (in the V-Ray object settings), you can also turn on the "Shadows" and "Affect alpha" options for it; in that case the shadows will be stored in the alpha channel of the image.

Best regards,
Vlado

[simmsimaging]

If you turn on the "matte" option of an object (in the V-Ray object settings), you can also turn on the "Shadows" and "Affect alpha" options for it; in that case the shadows will be stored in the alpha channel of the image.

Best regards,
Vlado

Ah, okay, I see now. I will have to see how it looks because turning the matte properties back on will reduce the quality again. I'll try it and see - thanks.

b

[simmsimaging]

An old one, but a recurrent problem at times.

If I'm trying to get a nice shadow pass to composite later - not simply a cast/drop shadow, but a pass of the self-shadowing of an object too. Is the only way via making my object a matte? It will mean rendering twice, because I want to keep the beauty pass and some other elements from the normal render, and I cannot get a decent looking shadow pass on the non-matte objects.

Is there a way to do it without going to matte objects and re-rendering? (the render times on my high res stuff can be prohibitive, so multiple renders can be a real problem on tight timelines).

b/

[pixela]

I have the same problem on the same day!

When I try to render a matte object with shadows, the shadow quality is so poor. I suppose you make a render without matte and then with matte and use the alpha channel from the second render on the first one.
Is this the way?