Sampling on render elements

[joconnell]

Hi Folks,

I've started using passes and multi mattes a lot more, largely for integration of backgrounds and what not and one thing I notice is a lot of the time I'm getting render elements that have a lot of sampling issues - for example in this element you can see that it starts breaking up on objects which are using the same materials in different areas - originally I though it was some kind of reflection of reflections type of thing but it seems inconsistent - more annoying is having a multi matte element where a straight edge gets broken and fizzy. I'm using fairly high aa (mitchell 1,12 and dmc thresh 0.003) which should cover multi matte sampling amply - any ideas on what might be causing it? Is vray having a hard time on areas that are getting quite weak amounts of reflection for example and doing a bad job of separating them?



Cheers!

John

[vlado]

The sampling of the render elements follows the sampling of the main RGB element; so in areas where the RGB difference is small and the image is undersampled, the render elements will be undersampled also.

If you are using the "Adaptive subdivision" image sampler, it may help if you turn on the "Object outline" and "Normals" options.

Best regards,
Vlado

[joconnell]

Hmm - on qmc 1 12 on this one - I opened up the file from the backburner network folder and it rendered the same thing, opening my main scene and loading the cached ir / lcmaps and rendering did a nicer job for some reason - haven't touched any of my sampling in quite a while so I must be doing something else dumb in the mean time - just the way it's breaking in certain areas rather than overall seems odd.

[joconnell]

Maybe not related to the above issue but found something out - objects that have vray properties to make them into a matte object (in this case alpha contribution -1 and affect alpha on) get poor edge sampling in the multi matte element - this is with aa 1 / 12 mitchell - the edges clean up totally when there's no vray properties applied.

Would it be something to do with the dmc sampler not looking at objects that have certain properties changed? I've had the issue happen before and it might be on windows that I had excluded from gi for speed reasons.

I use a lot of glossy stuff so I'd never switch to adaptive subdivision - it'd be great to find out what's causing this with qmc since it'd be too heavy to re render a full scene with different aa purely for the sake of an element.

Cheers!

John

[RErender]

looks like it could be unexposed/unclamped reflections?

[joconnell]

Hmm - rendering with clamp and subpixel on but yeah they're very flickery almost like overbright reflections - they dance around like hell too - I'm screening them over something else but they draw far too much attention - it is the raw reflection element alright, I opened the scene that made the image and turned on normal ref - same deal.

[RErender]

Are you you using vraysun and sky? might try making the sun invisible or try overriding the reflection map?

[joconnell]

Shall give it a go shortly!