render out reflections separately?

[stayinwonderland]

So I need to create a layer in photoshop with JUST my reflections on (mainly as a mask I think, at the client's request).

 

Is it possible to render out a base render with no reflections though? so I can keep the two apart?

 

I've never quite understood this process. I know it's going to involve rendering out an element but not sure which.

[Tommy L]

There's not a complete pass without reflections as an element. You'll have to run another render with reflections turned off. Unless you want to run all the passes, comp the render then turn off the reflection elements, but that will be more work than just re-running the render.

When you do your render with the reflections turned on you have a couple of options. You can enable the RawReflections, the ReflectionFilter and the VrayReflections. VrayReflection pass is the Raw Reflections already multiplied by the ReflectionFilter. I may have got some of the terminology a bit wrong as Im not in front of Vray right now.

Without knowing what your intended application of the render is Im not sure the best way to do it.

[stayinwonderland]

cool, right so I got some more info. I basically need to remove all of my own reflections but render out the information as to WHERE those specular/reflective parts are. It's to be camera mapped inside a game engine, so they provide their own reflection map to fake it.

[Tommy L]

OK, well there's a couple of ways to do that. Quickest/least painful depends on if the scene is already built and material-ed?

If it is and its quite complex, it may be best to render out 3 things:

#1: full render w/ reflection filter element enabled

#2: reflections turned off

 

You will deliver two files to your client, the result from 2 and the reflection filter.

 

If you are just beginning the project it may be best to flag the reflection channel in each material with some thing you can isolate in post.

[stayinwonderland]

It's already built and textured, so the first option would be the way to go.

 

Thanks very much for the advice, I'll give it a try and see how it goes!

[stayinwonderland]

Ok, been playing with this and it's a bit of a headache because the client wants just the specularity/reflection highlights as a mask. I think I can manage that with

 

I was a bit confused as to why my renders had lots of black in when I turned off reflection, then realised that the option includes refraction too. So first, why? Is there a way to just turn off reflections?

[stayinwonderland]

Hi there, if anyone can tell me how to render without reflections but WITH refractions that would be great... I'm pretty desperate to get this done asap. Thanks.

[Tommy L]

Hello Andy, you get it fixed?

[stayinwonderland]

Hey, not as such, I'm struggling. The only way I could figure out how to render without reflections but with refractions was to go through all of my textures and find anything that was transparent and turn turn reflection to black/zero. So then render:

 

1. reflection/refraction turned off (giving black, opaque glass)

2. above turned on but with glass/transparent materials reflection turned down to nothing

3. Cut out the glass parts by hand and stick them in a layer above

4. Then render with everything turned on just to get the passes for specular + reflection.

 

Surely this isn't right? Not even sure if this will work as I haven't tried it yet.

[Tommy L]

Hmm. Maybe you can turn of reflection and refraction and put a value in the Opacity channel of a material instead of refraction? I think Vray calculates opacity seperately from refraction but I may be wrong.

[stayinwonderland]

Could you explain more about putting a value in the opacity 'channel' of a material?

[Tommy L]

Channel is just another word for slot. Put a map in the opacity slot in the maps in the material editor.

[stayinwonderland]

Yep, that did it. Thanks!

[Tommy L]

So did it work out ok?

[stayinwonderland]

Thanks for checking back

 

Ummm, sort of. The actual requirement from the client turned out to be impossible though... basically render out an interior scene with furniture separately on a layer with its own shadows and specular etc. Sounds easy but keeping the ambient light of an interior but also making that interior a matte which also receives cast shadows... starts to slowly become impossible. So I just faked it and had to have no glass and airbrush the cast shadows.