Multiple Alphas

[fAEkE]

Is there any way to get multiple alphas from vray in one render?

[instinct]

Am not sure i understand what you mean. You can get different Mattes using MMREs, you can get alphas for specific object groups along with a matching RGB using VRayOBJSelect

Regards,
Thorsten

[fAEkE]

I meant if I can set Alpha IDs on objects, or something like that. Get alphas for different parts in only one render.

[rivoli]

as thorsten says, you can get different mattes, based either on objects or material ID, with the multimatte element. you can even stack multiple elements on top of each other, if you need more than 3 set of mattes.

[fAEkE]

Hmm, I have tried those element but I don't really understand how they work. I don't get alphas, only wirecolor-like renders.

[instinct]

The Multimatte renderelement is based on the fact that there are 3 distinct channels in an rgb image. red, green and blue. As they are completely seperate channels you can just take either of them and have an alpha (as in greyscale matte channel). This way you can have up to 3 alphas (or mattes) per element. You can have as many elements as you like and mix materialIDs and objectIDs as needed/wanted.

Regards,
Thorsten

[rivoli]

that's how the element works, even though you don't use the actual colours, but extract the mattes from the respective RGB channels.

[fAEkE]

Right, so they are pure red, green or blue. But thats three colors.. only three alphas?

Edit*
oh nevermind, you get it as mattes so different MultiMatte elements shows different objects.. more or less.

I guess that if (or should I say when) vray can output premultiplied alpha, this wont work very well?
Anyone know why vray can't output premultiplied alpha? We have had some major issues with that..

[instinct]

I assume you mean unpremultiplied ? MMREs and Alphas are both premultiplied by default. Turning off filtering for an MMRE results in unpremultiplied alphas. IF you need raw seperation, then you have to sperate beauties too. You can do that using the VRayObjSelect.

Regards,
Thorsten

[rivoli]

Right, so they are pure red, green or blue. But thats three colors.. only three alphas?

in a single element yes, that's one for any RGB channel. but you can add more elements, if one is not enough.

[fAEkE]

Sry, I meant that "When vray can output Straight alpha". I blame my current diet, can't use my head without carbs.. :P

Just disabling filter wont work very well, we can't use an alpha without AA? We need straight alpha for our comps. Is there a way to do that i Vray? Alot of ppl must have the same problem..

[fAEkE]

@rivoli
Ye I just tried it myself, works fine, but it's a pretty weird way to get more alphas

[dans]

I you need many "Alphas" and a streamlined workflow for that: MatteShooter

Daniel
psd-manager Developer

[fAEkE]

Thanks dans, I'll take a look at it!

[fAEkE]

dans, is that premultiplied or straight alpha?

We have more issues when working with AE than PS tho, so I dunno if that would help us.