Rendering the REFLECTION ONLY for ONE OBJECT in a scene.

[landrvr1]

I have tried figuring this out but cannot. Grrrr.

How in the world can you just render just the reflection on a single object in a full scene.

I've been trying to figure out the DoF issue with reflective glass, but without using the DoF in VRay cam. It's way too expensive.

I can easily comp frames together in AfterFX, but the last piece of the puzzle is just getting REFLECTIONS ONLY for ONE OBJECT.

A VRay reflection element will not work. It reflects everything in the scene, of course.

Can this even be done? An include/exclude feature in the elements would solve this 100%, but that doesn't seem to be an option yet.

Help. PLEASE! lol.

[Morbid Angel]

just render the entire reflection pass and use the multimatte to key out specific object.

[instinct]

I am not sure i understood what you need. If i got you right you want the reflection only of the whole scene in a single object. I'd say select the rest and set it "visible to camera" off.

Regards,
Thorsten

[landrvr1]

just render the entire reflection pass and use the multimatte to key out specific object.

Tnx.

Been struggling though with multimatte and how to set it up. I've given my glass an objectID in max of 5. I select matteID in the element checklist for multimatte, but I'm getting nothing but a black image. What am I doing wrong?

[landrvr1]

Okay, here's what I want to do. Very simple, right? lol.





This methodology would save enormous amounts of time as compared to using the VRay camera with DoF; an expensive process when dealing with a 3000+ frame animation.

And setting everything to 'visible to camera = off' just never works right. I end up getting funky things happening on the glass. Good in theory, bad in practice.

[instinct]

You have to set the IDs per multimatte element. Each can hold up to 3 mattes (for the RGB channels). So you add it, and then turn on all 3 channels and set one of the spinner to the ID you need (5).

Kind Regards,
Thorsten

[landrvr1]

(Thorsten, thanks for that. Got it.)

Okay, guys. I don't see how this is going to work. Here's what I've got:


main image


reflection pass


multimatte element

Okay, I'm back to where I started. The problem lies in the REFLECTION PASS. I guess I'm just not following this at all. I still don't understand how I can get an image where I just have the reflections occurring on my glass. That reflection pass is worthless because it's got reflections from everything in the scene. The keying out of the glass is easy. I knew how to do that already.

Am I not comping this correctly in AfterFX? Is it the format I'm saving in? Which is rpf?

I'm totally flabbergasted at this point. No clue as to how to do this. And, MY GOD, it seems like it should be so simple, lol.

[3DMK]

Does your Z-depth image have the glass in it???? if it does then that is why your glass reflection is getting blured as well.

You may find it easier to render your anim in passes - One without glass & one with the glass & a separate Z-depth for the glass & comp in separately.

Hope this helps

[landrvr1]

Does your Z-depth image have the glass in it???? if it does then that is why your glass reflection is getting blured as well.

You may find it easier to render your anim in passes - One without glass & one with the glass & a separate Z-depth for the glass & comp in separately.

Hope this helps

The Z-depth does have the glass in it, but the material is set to Affect Channels: All, so it's as good as not being in the the shot at all. The Zdepth pass ignores the material.

The problem with doing a comp like you described is that no matter what you do, or layer blend you use in AE or Photoshop, you will get a doubling effect of other reflections in the scene. In other words, the floor reflections above will be amplified; hence my need to somehow get a pass that ONLY has the glass reflections.

I just refuse to believe that VRay isn't capable of doing this, lol. (!)

[dlparisi]

Does your Z-depth image have the glass in it???? if it does then that is why your glass reflection is getting blured as well.

Removing the glass from the z-depth image won't clear this up. It'll give him exactly what he has now since it will assume the reflections are actually an image on the back walls and blur them accordingly. AFAIK, there's no straight way to do this with a single image and a z map.

What he might try though, depending on the scene and materials, is to use the scene as rendered together with a few other passes, namely the refraction and refraction pass along with a Multimatte to mask out just the glass. Render the scene as normal with the z pass but add the additional passes above. In AE, take the straight RGB render and layer over it the refraction pass and then the reflection pass, both using the multimatte as a track matte for each of them (you'll have to convert the multimatte R,G or B channel to grayscale). Set the reflection pass to 'add' and z blur both your rgb pass and your refraction pass. It is very important to be working in linear space with this so everything adds correctly (set AE space to 32bit and "blend colors using Gamma 1.0") and I save linear EXR's for the images, it won't work otherwise. Again, depending on the scene and materials this should work (I've used it for stills before).

[landrvr1]

@dlparisi

Hmm. I'm going to have to get my head around that and give it a try.

What I gather then, gents, is that VRay is incapable of rendering a pass with just the reflections of one object? Because that is the absolute easiest way to do this, bar none. Comping a one object reflection in AE would be child's play.

?

[dlparisi]

One thing I misstated was concerning the z-depth pass - there's no way to have the glass ignored while generating the z-pass and still get all of the correct other passes. So you'll still have to render out another pass to get the z map you need, at least you can do it though with no GI and very low settings (you could even have all lights off) to render very fast.

I'll try to post a simple AE setup with all of the passes tomorrow.

[landrvr1]

One thing I misstated was concerning the z-depth pass - there's no way to have the glass ignored while generating the z-pass and still get all of the correct other passes. So you'll still have to render out another pass to get the z map you need, at least you can do it though with no GI and very low settings (you could even have all lights off) to render very fast.

I'll try to post a simple AE setup with all of the passes tomorrow.

Tnx for that, dlparisi. Sounds interesting. Hopefully the next version of VRay is going to have the ability to include/exclude objects in the reflection element dialog.

[sany]

Sorry Landrvr1 if I've got this wrong..

why don't you just uncheck the seen by reflections/refractions in the max object property for all objects you don't want to cast reflections and then set all objects in the scene to be Vray properties matte objects.

When you render the reflection pass you'll then get only the object reflection you wanted.

Admittedly you'll need to render a separate stream but should be pretty quick if you've saved IR etc.

Is that what you wanted?

[dlparisi]

Here's a quick scene - there's a shet of glass between the red and blue teapots. The first one is the regular render using AE lens blur. The second one is the layered reflection also using lens blur but adds the non-blurred reflection to the blurred refraction which is over the normal RGB.



You can downoad the AE (CS3) file at http://dpict3d.com/vray/Fake_DOF.zip

Again, this works but is not for every condition as it can lead to edge problems around the glass (from the blur) and it also seems to work best with very clear glass.