Vray multimatte Material ID, poor/inaccurate results.

[irwit]

Hi all

I have a blend shader with Shaders within, Leather and stitch, the stitch shows through with a mask. These 2 shaders have different Effect IDs.

However when i render the multimatt is way off compared to where the RGB image is, images attached.

Basically the Multimatte is far thinner than what is actually shown in the beauty, and is to the pont that when the object is far away it renders none of the stitch map at all, its an empty channel? But the stitch can still clearly be seen within the beauty.

Is this is a known issue with MultiMattes? This is kind of making Multimattes pretty useless for me :s

Any help much appreciated.

Thanks

Will

[irwit]

As the 2 images separately don't show that well how big the issue is, here is a combination The bright green is the difference between where the stitch shows on the beauty and where is shows in the mask.

[Morbid Angel]

did you try - consider for anti-aliasing option in the multimatte?

[irwit]

The edges are anti aliased in the multimatte image ???

[Morbid Angel]

in some certain conditions, the multimatte may not get sufficient sampling from the primary buffer, that's why you can use that option. Alternatively, you can increase min samples in the dmc sampler which should produce similar result.

[irwit]

If will definitely try that tomorrow but because of the difference between where the mask is and where the multimatte is, I'm really not sure that AA will be the issue here.

I sent a test with the mask in the extra texture and that rendered as expected matching up with the beauty perfectly, so in a worst case I can use this as a mask, but the issue is still there.

I will send a test with fixed sampling and let people know the results.

[irwit]

Morning all

I have tried again this morning with fixed sampling and still no joy. I have included a new render to show what is happening, with blue lines drawn in photoshop to show the difference between each pass. It seem the multimatte is shrinking the mask by a pixel or 2. So the left most red and green is the beauty using a Vrayblend with a red shader in one slot, a green shader in the other, both having different "Effect ID" numbers, mixed using black and white map. The middle image is the multimatte ID result, you can see how much smaller the stitch area is compared to the rgb. The final black and white image is the mask used in the Vray blend added to a Vray extra texture.

So there is definitely an issue within the multimatte ID render element here???

[irwit]

Finally, here is the multi matte ID with channels changed to produce a black and white on the left. I think this best shows the issue. These images should be identical.

[Morbid Angel]

maybe you can post a part of your scene?