Complex Matte Render Setup

[ozztheforester]

Hi,
In a recent project we had a huge headache and couldnt find a proper solution and ended up doing whatever worked at that time in sake of delivering the project.

Here is the question..
Lets say we have an interior+exterior animation already rendered without people with static gi and non moving objects..
And client comes to us asking for adding people (3d not so highly detailed ones).
Because of the scale of the scene we need to use hundreds of characters so vray sphere fade is not an option there..

All we can do is rendering people in matte layers and composite them onto already rendered backplate..
However the lighting on the backplate is complex there are many shadow and lit areas which requires some sort of isolate shadow option for any given object.. And reflective refractive walls and flooring..

How would you do the matte setup on a complex scene like that?
I am sending a sample scene to explain better,
1-there is a room with some louvers on top allowing sunlight to come in
2-there is an animated object (this is the object thats to be rendered later )

Problems we had,
1-Couldnt find a solution to do shadow isolation for people (animated objects)
2-Couldnt find a solution to effectively render out only the reflections and refractions of the people..

Thanks alot!
matte test01.zip

[Neilg]

Render the ground with the people but a black environment - render another pass with the people as a vray light material and black environment. that'll be your mask for reflections.
Use the raw light and raw shadow passes from your original base render to mask between the shadow pass from the people (when they're in direct light) and a vray dirt/ao pass (when they're in shadow)
We always do glass as a separate pass so refractions get handled (and faked) in post

[ozztheforester]

HI
Thanks for sharing your methods,
We have also been relying on black environment while adding other objects to already rendered scenes, however it's hard to find an unambiguous method of rendering additional object mattes.
However as the composition assets gets more and more complex it becomes harder to manage the project especially considering our clients are asking for 2-3 minutes of animations in less than 2 weeks sometimes..
Do you know is there any specific fire and forget method available in vray to isolate shadows and perhaps the reflections of any given object, I am sending an image to explain better.
Cheers

[svetlozar.draganov]

You could use Exclude (Shadow Casting) option available in each Vray Light in order to remove unnecessary shadows.
According to the reflections, we would need a better example of what exactly do you want to do - in Vray 3.0 there is a Reflection Exclude option which could help to isolate unwanted reflections. Another option would be to use Render Mask option with texture input - this workflow requires pre-rendered MultiMatte masks where the material of the reflective object have Affect Channels option set to ALL.

[3dwolf]

Having the same problem right now.
In VRay pre-3.0 it somehow was possible to have matte-material-objects to only cast shadows on visible objects but not on other mattes, and the visible-non-matte-material-objects casted shadows on the matte-objects. This was when there was a standard-material in the wrapper-material. So the new objects in shadows were shaded and casted a full shadow on the ground but the Houses and trees did not create double-shadows.
Want: "Don't cast shadows on other mattes"