Matte wrappers not working as expected...

[Neilg]

I'm trying to break an animation down into layers - one with the background, one with the people including shadows so I can layer them over each other.

I've been trying to do this with the mtl wrapper, but it's not working how I expect it to.
My problem is, when I turn on matte object/recieve shadows, it doesnt act as a mask for the light - only objects.
Suddenly everything is casting shadows as if hit by the sun - it's passing straight through the walls and ceiling.

Here's a render of what I get with normal materials, and then the matte surface wrapper on them all:



What I want from the second render is those diffuse shadows in the alpha, people cut out with similar lighting to the top one, and the shadows from the sun just cutting through where the holes in the ceiling are.

Incidently, what i've gathered so far is that everything I thought I knew about how mattes work is quite wrong and I actually dont know what i'm doing.

How would I go about getting what I want?


Thanks in advance

[instinct]

I'd say make the floor matte object with alpha contribution -1 and tick "shadows" and "affect alpha"

Regards,
Thorsten

[Neilg]

Done that - if I leave the walls as they are (normal vray mat), they show up in the render (which I dont want)
But if I do the same to the walls, they let light pass through.

They still mask out the people if they pass in front of them though - so it's managing to block them. It just cant block light?

edit: If I leave the walls with the normal vray material but change the alpha contribution to -1, they let light pass through... This cant be right, can it?

[instinct]

Well the floor is a matte object to then right ? Because by default matte's dont cast shadows on each other. You have to untick "No GI on other mattes". The name is a tad misleading. Or have a shadowcaster that is set to "Visible to camera" off in the standard object properties.

Regards,
Thorsten

[Neilg]

But then the entire room renders in the alpha, apart from where the sun hits because it classes it all as being in shadow...

I guess I want the matte wrappers to block the light without it thinking theres a shadow cast by it - as in, only the normal objects actually cast shadow - the matte objects that cast shadows just get it blocked and not show up.

Is there a simple way to do what I want?

[vlado]

There is an option in the matte settings called "No GI on other mattes" - is this on or off?

Best regards,
Vlado

[Neilg]

It was on before - with it turned off, none of my shadows show up in the alpha.

[Neilg]

Here's it with it on:



Which I think is correct as far as vray goes, but I was expecting it to do something else.

It's got the shadows around the people, which is good, but it also catches the shadows from the walls and ceiling. So I figure the only way to actually do this is render one like this, then render another without the people and do some compositing tricks to get an exact "people + only their shadow" pass. Unless i'm still missing something?

[Morbid Angel]

what you need to do is basic component separation and comping:

Get everything except the people and make it - not visible to camera...render your people.
Get your people make them invisible to camera and render your background environment
Get your ground plane and make people invis to camera and render just the shadows.

Now you will have 3 elements which you can composite to get the result.

[Neilg]

Sorted, thanks guys

I was just being silly and expecting it to read my mind a bit. haha. Still got limited experience with proper compositing.

[duke2]

Mind saying how you did the people? From scratch from reference? Or poser or from AXYZ people as a base or something?

[Neilg]

The models are AXYZ, we've done a full re-texture and the materials from scratch so they look pretty good now.

Figured out reflections in floors now too, I shouldve got into compositing long ago...

[Donald2B]

How did you go about setting up to get just the reflections in a seperate pass?