Matte Pass problems

[Morbid Angel]

on the second note, its incorrect when vray sun is active...I think this is the key problem.

[gilpo]

Thanks for your help, Morbid. Glad to know it's not just me (which wouldn't have surprised me).

It seems it's not just the vray sun. When I change the light type to a standard light, it does the same thing (not quite as severe, though, but it is a little brighter). It's either a physical camera bug or a matte bug. Seems the vray sun amplifies the effect. Let me know if you have any other ideas.

I sure hope Vlado checks the forums on the weekend...

[Morbid Angel]

well for now you can cheat it...do it per pass manually i suppose and composite it with alphas.

[gilpo]

Well, see, here's the thing. I've already rendered the building. Now I'm trying to render animated 3d people to composite into it. Not sure how to cheat that... Got any advice?

[Morbid Angel]

There is few ways to go about this:
1 - you can use sphere fade pluging and go through vlado's tutorial where he does exactly what you need.
2 - you can render your people with the house set to be invisible to camera (background black). This will render people without occluded matte. You will then make an occlusion matte of your own, where animated people will be pure white and house pure black (no gi or anything like that, just black and white.) Then in comp use that matte for your animated people.

[Morbid Angel]

you may also need to do a custom pass for people's shadows. I would suggest to use a combination of occlusion and direct light passes for that.

[gilpo]

Ouch, the occlusion matte pass sounds painful. Especially since parts of the building itself occludes people.

Have you ever used the spherefade in this manner for an interior? If so, what kind of GI quality settings do you think I could get away with?

I appreciate all the help you've given.

[Morbid Angel]

Ouch, the occlusion matte pass sounds painful. Especially since parts of the building itself occludes people.

Have you ever used the spherefade in this manner for an interior? If so, what kind of GI quality settings do you think I could get away with?

I appreciate all the help you've given.

Not at all...I will wip up a quick example for you.
Meanwhile read this its a tutorial on how to use sphere fade.
http://www.spot3d.com/vray/help/150R...rials_anim.htm

[Shimakaze]

Im running a different vray version, however this may also work. Here try this scene, it does what you would expect with the matte.

http://www.novuscom.net/~marina/matte_scene.rar

It gets even funkier if you add reflection to the matte object and the sphere and put an image in the reflection environment override

[Morbid Angel]

So here is a quick comp example:

we have a scene which has been rendered



we render the people on its own, with the scene set to be invisible to camera



render the matte where people are pure white and house is black



render the peoples shadow



composite flow



final result

[Shimakaze]

How would you go about adding reflections? Say, if the floor and the "people" were reflective? (aliens are people too!)

[Morbid Angel]

well it only gets trickier from here on. Since you didnt render people and the house in one pass, to derive proper reflections from one to another will be difficult, if you look for accuracy. If the people are reflective, then the same method applies as I described above, except instead of rendering the people you will render (people RGB + people Reflection pass.)
However for the floor its a bit more tricky. Since you need the people to be illuminated by the gi bounce from the house, yet not visible to camera and reflected in the floor. There are some methods that can make it work, like projecting the people's render back at the models via camera map WSM and rendering that in the floor reflection.
What I would attempt first is to try to cheat the floor reflections in comp, if that does not work, then more complex approach would be required from 3d.

[sv]

Morbid,

would you be able to describe the flow above for someone trying to learn all this?

From what i can see -

Input - Background RGB
Input - Matte for People objects
Input - People RGB

something like
(*)Channel copy Alpha Matte into People RGB
(*)Merge People RGB over Background RGB using Alpha Matte (over or plus)
(*)Invert (?) and colour adjust People shadow over Background + People

Is that kind of right? Little confused how you add the shadows to the comp.
Thanks

[Morbid Angel]

Morbid,

would you be able to describe the flow above for someone trying to learn all this?

You got the basic idea right.

1 - background
2 - people layered over background using custom alpha (people matte), layering metod is normal, not additive just a standart over.
3 - shadow is used as a mask in a color corrector, to drop the color gain on the image. Since the shadow cannot be just layed over or multiplied, I typically use it as mask to color correct the actual image. And if the image is float, like what we usually work with, then this can produce some nice results.

[sv]

3 - shadow is used as a mask in a color corrector, to drop the color gain on the image. Since the shadow cannot be just layed over or multiplied, I typically use it as mask to color correct the actual image. And if the image is float, like what we usually work with, then this can produce some nice results.

ahh, cool, nice tip.
clever - never thought of that...