Multi matte / Wire color / material id differences differences

[thanulee]

Hi, what is the difference between these 3 elements? I know that in multimatte you can have rgb colors with G buffer ID (though i can have only 3 from what i tested), in wire color is the color of your object and in material id is the material id you give (it gives me jagged edges though).

 

So i was wondering, why not to use just wire colors cause its the simpler and needs no setup just adjust the colors? I mean i use this passes for selection only. What is the actual difference? Is it a matter of preference? thank you

[Corey Beaulieu]

None of them are filtered, so you are always going to get jagged edges, but the main difference come is the selection. Multi-Mattes can be selected through the channels and, in my opinion, has a much cleaner selection of what you want over the other 2. Mtl-ID, is cool because you get the material groups and Wire Color is done on an Object-by-Object basis. I use script to get wire color by material, but ultimately the risk is that multiple materials get colors assigned that are too close to one another and PS cannot cleanly select them.

 

I do use them all, but rarely do I let the wire Color or Mtl-ID assist in final paint. The best matte is to just turn off Lights and GI and use the Override setup to get a nice, clean, and Filtered alpha matte.

[thanulee]

Thanx, yea i noticed that multimatte has a cleaner selection. It gave me some trouble with the g buffer ids, then i understood i can only have 3 objects per pass. What about this method u saying? can u explain it to me a bit more? thank u

[Corey Beaulieu]

Alpha Matting?

 

I usually use a MaterialWrapper with a Vray MTL set to non-reflective black in it as a base. Then set the Wrapper to Matte/Alpha -1/Affect Shadows/ Affect Alpha/ and then place this in the Override section of the render settings. Using the exclude menu, I exclude the objects that I want a matte for. With Lights and GI turned completely off, the Mattes render really quickly, but will be nearly black. All you want is the alpha channel as a perfectly filtered matte for the best selections.

[notamondayfan]

You might want to look over my blog post and script I wrote to control the Material IDs and how to render them. The script also organises the IDs so you know what IDs have already been used.

 

http://arddigital.co.uk/effect-id-changer/

 

For me, generating masks by material is the best way to go, as when I'm doing adjustments in post I would want to control the material properties, not groups of objects.

 

Dean

[thanulee]

Yes Dean, most times the material properties are the thing we want to improve. I ll check it thanks a lot. Btw, i ran into some interesting method that works great (i think it would work on animation too). You can change to scanline renderer and render with complete black or complete white without lights or gi, the things you want to isolate as selections. It is super fast and efficient though I cannot see the downside of it yet. For my case worked as a charm. Thanks again

[John Dollus]

Depending upon your sampling settings and detail, switching to scanline will result in sloppy mattes as the plates won't match up around the edges

[Francisco Penaloza]

VRay ussually have different ways to solve the same problem, MultiMattes, VRayMtlID, VRayObjectID and VRayWirecolors are one of them, the difference I would say space (bytes) and properties, Multi Matts are very small files and can keep transparencies, also they are stored in channels, (R,G,B) this make it pretty efficient to work with in After effects, Nuke and so on. the only "problem" is that you can fit on 3 at the time so if you need more you need to change the name of the multimatt, such, MultiMatt-1,MultiMatt-2, MultiMatt-1, and so on. this can be a pain if you want 100 of them, but working with multichannel exr it make it a little more workable.

VRayMtlID, VRayObjectID same function but they can not store transparencies. They can be stored as integer this make it very light in rendering time but you get jagged edges, or you can save it as color(pixel) but it increase render time because the antialising, not that much but again if you have several passes each one of them count.

VRAyWirecolor, it is antialised, ans it work as it name describe.

You can mix and match depending of your workflow, for instance if you are rendering a City, you can separate on Materials ID, use wire color to isolate Buildings and Objects ID to isolate Blocks and so on, trees, cars and what not.