Matte Pass problems

[gilpo]

Morbid,
Thanks so much for the example. I'm sure it will help a lot of people here (me included). Just a couple more questions then I'll leave you alone. I'm sure you have better things to do .

1. I'm good on all the passes except the shadow pass. How exactly do you go about setting up the scene and rendering that?

2. I'm using the MultiMatte render element for some other things, but would there be a way to use it to eliminate having to render so many passes? It seems like it would work, but I just can't get my head around how to integrate it into the process you outlined. Or can you think of any other tricks that could streamline this any more?

Thanks again!

[Morbid Angel]

Well like I said in the previous post, it only gets more complicated from here on. Having to combine two separate elements into one, where one deeply interacts with another is quite complicated.
About multimatte, the only purpose of that is to make user controlled channel ID's based on RGB channels. The idea is to render everything at once and use multimatte to generate masks to control in post.
About the shadow, basically I specified that the light source (area lights in windows) are the only thing that is illuminating, no gi or anything like that. Then the interrior itself was made to only recieve shadows, not cast. This way it only gets the shadow from people, not from itself or other objects around, since that information is embedded into the background image already. And the interrior is set to be as a matte object with alpha contribution -1...

[sv]

And if the image is float, like what we usually work with, then this can produce some nice results.

exr?

[Morbid Angel]

yes, exr, 16 bit png etc...exrs are best because they are really small, they have many functions. I would say anything other then 8 bit would be a good choice. However working with exrs, or floats in general the typical gamma corrections methods change somewhat.

[Da_elf]

this is the matte problem im having, that light brown area seen through the windscreen is the ground which is set to matte in the vray properties. i could reeeeally use a fix for this asap



before you ask yes i have affect alpha turned on in my glass settings (would fog have a roll to play in this? all of my standard glass has fog in them)

[gilpo]

this is the matte problem im having, that light brown area seen through the windscreen is the ground which is set to matte in the vray properties. i could reeeeally use a fix for this asap

Yeah, we're having that problem trying to comp our animated cars into a pre-rendered scene. We've been trying to workaround this as well with no luck.

I have narrowed down the other problem, though. It seems when you make an object a matte, it stops casting shadows.

It really sucks when you go all the way through production, expecting something to work in the end and then get to deadline and it's broken. But I suppose that's my fault for not testing better.

I really hope Vlado has seen this thread....

[RErender]

You could adjust the "alpha Contribution" for the glass to .1 or something then adjust like you like it in post adjusting the alpha levels.

[Da_elf]

rerender can you explain that? ive got the alpha contributor of the ground set to -1

[RErender]

rerender can you explain that? ive got the alpha contributor of the ground set to -1

Set it to .1 (or 0.0 but that still has a slight alpha contribution) for the glass and you'll get a semi-transparent alpha for the glass, then in you compositor you should be able to adjust the "levels" of the glass' alpha.

[Da_elf]

that looks horrible and messy

[RErender]

that looks horrible and messy

LOL, worked for me in the past

Can you post an example?