New G-Buffer and Render Elements

[GRIFFIN]

I've been reading up on the new G-Buffer and render elements that VRay can output in v1.45.70 and had some questions about how to implement them into a composite.

What can the Normal channel be used for and how would you use it? I've heard it can be quite useful, I'm just not sure how.

How do I use the object velocity channel to add motion blur to an image? (I use Combustion).

Does object velocity work on particle systems?

Does object velocity work on objects that have non uniform transforms on vertices? (Eg. attach a box to a sphere, go to sub-object vertex level and animate the vertices of the box over n frames).

I'm sure I have more questions but that will do for now.
Thanks.

[Phantastica]

You can use normals for all kinds of cool things in post. You can selectively colour correct surfaces based on the direction they're facing. If you have a bent normals pass (where the normals represent the direction that the majority of their diffuse light is coming from), then with a bit of trickery you can do a good job of simulating extra fill light, or you could do a lookup on an environment map and mix it in. Normal passes are generally a good utility pass to have around just in case.

The object velocity channel would be used with a Vector Blur operation. Combustion might support this. There are probably some After Effects plugins that can handle these too.

[Trapezium]

GRIFFIN: The Operator is called 3D Motion Blur in Combustion and it should just pick up the Velocity channel in your RPF.

Phantastica: Thanks for the info on Normal channels. I'll be playing around with this feature soon.

--Jon

[GRIFFIN]

Thanks for your responses Phantastica and Trapezium.

I just tried "RPF Motion BLur" in Combustion and rendering with the new build of VRay (v1.46) - it worked fine. This is something that I couldn't get working in v1.45.70 so I'm glad it's fixed now.

Phantastica: Thanks for the tips on the usage of bent normal passes. I am keen to check this out.

Trapezium: Any ideas on how to apply this in Combustion. A compound RGB selection maybe?

[Phantastica]

I'm not sure if vray outputs a bent normals pass, but mental ray probably would. To elaborate on this further, the RGB values represent worldspace XYZ co-ordinates. If you were working in photoshop, then you could probably use Curves or Levels to adjust the individual RGB values to bias the direction of any additional "fake" light. Then just desaturate the result, multiply it against a constant colour (your light colour), and mix it in with your original render.

It's pretty far from being physically correct lighting, but it can be a great artistic tool. I'll try to do up a tutorial if I have a chance.

[GRIFFIN]

Phantastica that would be ...umm..fantastic if you could. This is rather new ground for me so a tutorial would really be a great eye opener. I'm pretty sure that Vray does the bent normals pass. I've had success rendering it out as a seperate element. Just haven't quite figured out its implications. From what you say though, it sounds rather useful.

[Phantastica]

One other use for a normals (or bent normals) pass that comes to mind is for adding an edge treatment to your renders. In this case, it doesn't matter which pass you use, and in fact, the regular normals pass may work better. By running an edge-detect operation on the normals pass, you should be able to get a pretty good matte that you can use to add a bit of edge blur. You'll probably need to adjust the contrast of the matte after running the edge-detect and you will want to blur it a very slight amount. But by using this to selectively blur the edges of your objects, you can really make your images look more "filmic" (is that a word?). It helps take off the hard edge that most renders have and it simulates the natural diffusion that you'd expect from something shot on film with a real-world lens.