Multi Matte Render elements

[Bundie]

I read in 3D World magazine issue 116 in the Pre Viz-Architecture section that they render the entire scene and they use render masks for all materials using MultiMatte render elements, as to have full control of individual materials in Photoshop

I guess my question is, how is this done?
I looked in the render elements rollout but could not find any multimatte option.
Is this a VRay option?
Im a MR user

[MrTom]

It's a VRay thang.........its top of my list.




Sorry to dissapoint.

Regards.

[Bundie]

darn it,
anyone have a workflow for Mental Ray???

[MrTom]

I'll look into it....although I know jack about MR I'll try and see exactly what it does in VRay and try to replicate it in MR.

Can't do any more than that for ya I'm affraid.

Regards.

[MrTom]

Ok.....not sure if this is right but it looks to be about the same.

The Scene:





Rendered with MR and VRay respectively:







What VRay MultiMatte element does is to assign an RGB channel to the object which can then be separated as Alpha channels for each object and saved as such. From what I can gather you can do this for a whole object or for the individual materials applied to it.

VRay MultiMatte Element pass:





All 3 Alpha channels are stored in this one pass (I guess thats how it got it's name), which means that by using the RGB channel selections in the render frame buffer each object can be isolated and its Alpha channel saved....in this example The Teapot is rendered as the RED channel...the Sphere the GREEN channel......blah blah blah.......zzzzzzzz

Incidentally, the wire colours assigned to the object have no effect on this type of pass....the colours above are the 'Channel' colours ie RGB and NOT the material colours.....because I didn't apply any materials. In my haste I thought making the wire colour rgb too would simplfy things but no.......so forget the wire colours, it would still look like this no matter what colour the wire colours are.

Mental Ray can do the same thing but slightly differently.


Mental Ray Matte Element Pass:

Matte Element ID 1:


Matte Element ID 2:


Matte Element ID 3:




Each object gets its own pass in its own frame buffer, but is esentially the same as the VRay one.


To do this using Mental Ray I first selected each object in turn and assigned it an 'Object ID'....I'm guessing you could do this for each material too.

Object Properties:





In my example The teapot has Object ID 1, the Sphere is OID 2 and so on.........

Next, In the render elements I added a 'Matte' element for each object and assigned each one with a different ID. So the first 'Matte' element is ID 1 and will render the Teapot...which is Object ID 1.....and so on and so forth.


Render Elements Matte:





As far as I can tell thats about it.....I've never used it in VRay I admit and so there may be more to it than just this but hopefully this is the angle in which to attack Mental Ray to achieve similar results.

BTW, as I don't use MR as a rule all my MR setting were at default...I just switched to MR as the renderer and rendered...apart from adding the 3 Matte elements everything was standard.....including just a wire colour for the 3 objects...no materials applied.

Regards.