Matte object illuminator lights

[LudvikKoutny]

Hi,

I am wondering if V-Ray has any concept of illuminator lights for integration of CG objects on real plates. Basically, when it comes to matte objects, lights need to be divided into two categories. Lights, that were already captured in the scene at the time plate was shot, and lights that are being added to the scene afterwards. Right now, V-Ray handles the first case, but I can not find anything about handling the second one.

Basically, right now, if I create V-Ray light, it does not illuminate matte objects, but adds dark shadow into the scene. What I need here is to have a light, that adds light to the scene, but without shadows. Think for example headlight of a CG car added into the real scene. They should add energy on top of the plate.

What may be even trickier here is the fact I need that light source to be PhoenixFD fire

[new.ages]

Having the same problem.

The only way to work around this issue i found is to use objects with a VrayLightMaterial to illuminate the scene.
But you have to untick the direct illumination checkbox.
As far as I know you can only get GI on the matte objects.

[vlado]

Currently you will need to render the headlights separately in a second pass and composite them afterwards.

We could add two different types of lights, but in all these years this has never been requested until now even though renderers like iray have had it for a long while. Which makes me think that either it is not terribly important, or the requirement to render a second pass is acceptable. You are free to try and convince me otherwise though

Best regards,
Vlado

[LudvikKoutny]

Currently you will need to render the headlights separately in a second pass and composite them afterwards.

We could add two different types of lights, but in all these years this has never been requested until now even though renderers like iray have had it for a long while. Which makes me think that either it is not terribly important, or the requirement to render a second pass is acceptable. You are free to try and convince me otherwise though

Best regards,
Vlado

Well, since 3ds Max is not very good at render pass management, separate light passes are quite a big workflow seam for me. Another thing to consider is that general workflow is currently moving from multipass compositing to rendering everything in single pass, as the technology progressed quite a bit past few years.

Obvious con to this is another UI clutter, but I think having one additional checkbox in V-Ray light and V-Ray LightMTL (and eventually PhoenixFD fire light settings) would not be that much of a disaster. This theoretical checkbox would have an effect only of a given light source would illuminate matte objects, and would have no effect on regular non-matte geometry. And would be off by default.

It's just that there have been quite significant improvements in terms of CG to plate integration in past few releases, so with this thing added, I can't think of anything else that would stand in the way. V-Ray would then have complete, robust feature set for integrating CG objects into real world footage.

To be honest, I think the reason why it wasn't requested is that there's surprisingly only very few people who know how correct CG to footage compositing should work I've seen all kinds of terrible things people do to achieve integration even in very big VFX houses. Things, that often require a lot more effort to get the result looking right.

There have been a few quite wrong things with how matte objects work too, yet almost no one noticed them over the years

[jasonhuang1115]

Very interesting idea and can you provide some examples or even links to elaborate this?

So for example, in the plate there is a street lamp and an actor. A CG robot will be integrated between the street light and the actor. You create a cg light to represent the street light. It casts the cg robot's shadow onto the matte object that you created for the actor.
Meanwhile, the robot's eyes happen to shine lights onto the actor so you need a specific light type/function that represents the robot's eyes and lights up the face of the actor (i.e. lights up the matte objects in the scene)?

Also, can you name a few terrible things people do to achieve integration in big houses? and what is wrong with how matte objects should work?
Just very curious and would like to know.

Thanks,
Jason

[LudvikKoutny]

Very interesting idea and can you provide some examples or even links to elaborate this?

So for example, in the plate there is a street lamp and an actor. A CG robot will be integrated between the street light and the actor. You create a cg light to represent the street light. It casts the cg robot's shadow onto the matte object that you created for the actor.
Meanwhile, the robot's eyes happen to shine lights onto the actor so you need a specific light type/function that represents the robot's eyes and lights up the face of the actor (i.e. lights up the matte objects in the scene)?

Also, can you name a few terrible things people do to achieve integration in big houses? and what is wrong with how matte objects should work?
Just very curious and would like to know.

Thanks,
Jason

Yep, it's pretty much as you described it. You can see example of how illuminator lights work here: https://www.youtube.com/watch?v=VGZOOdTMg0E

As for what's wrong with V-Ray's matte objects - not much anymore. There was quite a few things wrong, such as screen mapped backplate leaking through GI and reflection requiring environment overrides, matte objects receiving a lot more GI illumination than they should, matte objects receiving negative illumination when used in conjunction with Dome light, matte objects not rendering correctly in reflections, no option to have matte objects screen projected in reflections and GI but black when viewed directly, matte objects having double reflections when used with dome light, etc... BUT Vlado has manged to weed out most of them (all of the ones I mentioned except the last one with double reflections when using dome), and is continuing to do so. So it won't be long before they are all gone

About weird things people do even in big houses, I know a few guys from places like framestore, MPC, etc... and from what i heard, for example:

- Taking beauty channel with alpha and doing over on top of the plate, then masking matte parts with some ID mask and manually tinting the shadows the same color they were in beauty pass, to get for example blue shadow in daylight conditions. That's completely wrong. Correct way to get 1:1 with beauty is to render colored alpha as separate render element, invert it, multiply it on top of the plate and then add RGB on top of it.

- Using shadow passes instead of mattes to integrate scene elements (non additive compositing resulting in all sorts of fringing problems, that would then be solved by ugly hacks like eroded alpha channel)

- Rendering completely without mattes and just slapping ambient occlusion on top to ground objects in the scene

- Few of them don't even know the concept of plates being projected on the matte objects, which then reflect and bounce on CG objects. They would often just use HDRI from the location without doing scene blockout and projecting the plate.

- Matching scene lighting manually by random lights instead of HDRI from location or HDRI of similar character

- Rendering reflections of CG objects on mattes in separate pass, and then compositing them over by simply adding them, resulting in glowing or too dim reflections.

There was a few more, I just can't recall at the moment. It's just that most people (mainly compositors) in general will still expect you to give them just beauty pass of just CG object without any shadows around, and some monochromatic shadow pass, and AO pass, and that they will somehow fiddle the crap out of it until it looks right. Such ancient workflow, let alone that any bounced GI light from CG objects to plates will be completely taken out of equation.

[thanulee]

+1 for this feature. If its simple to do, would help a lot in compositing

[jasonhuang1115]

Thanks Recon442. I saw you posted several threads regarding matte objects workflow. Will digest through them in a bit.

[LudvikKoutny]

Thanks Recon442. I saw you posted several threads regarding matte objects workflow. Will digest through them in a bit.

But keep in mind most of those things are not relevant anymore. As I said, Vlado has fixed almost all of them.