Help Rendering Layers for Compositing

[Donald2B]

Okay, I am a total newb when it comes to compositing. I have been working with Tim's new training DVD from Gnomon and it has been fantastic. After going through all of these tutorials and training DVDs I now have more questions about getting passes out of VRay.

I want to be able to do the following:

--> Render Background (already know how to do this)
--> Render Building by itself (mostly have this figured out)
--> Render Foreground elements (Trees, cars, bushes, etc. and have their reflections on the building (no clue!)

In our pipeline, we are more of a design tool than a final render house, so the building is constantly changing with a very short turn-around. So if the foreground elements were setup with reflections all ready to go, just drop the building behind them and we are good to go. Is this possible? I feel like I am WAY over my head here. I tried searching, but I am not certain about what I should be searching for.

Thanks for any insight into this.

[MoonDoggie]

We are currently working together to make a solution to rendering matte passes in another thread: feel free to watch our updates here.

http://www.chaosgroup.com/forums/vbu...ad.php?t=42454

Also search for "basic comping of a vray render" which will have a very in depth view of comping (more than you're looking for by the way)

[Donald2B]

Collin, thanks for the information. I've read through Chris's Great tutorial about the render passes and that helped me out immensely when I first started to get things figured out. I am still trying to work through the other thread that you have started with the matte passes.

I am just finding it difficult to get just a reflection pass to render by itself without having to render everything else. Unfortunately, I don't have access to a large renderfarm and so I am trying to work out some alternatives.

Thanks for the help and I am going to keep plugging away and see what I can some up with.

Best Regards!

[MoonDoggie]

No problems, I am still figuring it out as I go as well, no worries, keep us updated on how you set them up as you learn and it to will be a valuable resource in the future for others.

[Donald2B]

Once I get this all figured out, I will do a complete write up. I have been working on this for the past couple of weeks from the ground up. Figuring out how to put all of the passes together using the render elements was pretty simple. It helped that it was highly documented by Chris Nichols's great thread here and Tim Jones' Gnomon DVD on Multi-Pass Rendering.

The only thing I am hung up on now is trying to get those same render elements from VRay to render by themselves. Reflections on top of reflections are really giving me some troubles. So I am assuming that I just don't quite have the fundamentals/theory of this concept down.

Again, thanks for all of your hard work on those scripts and to everyone else here who has been so gracious with their knowledge!

[RErender]

--> Render Foreground elements (Trees, cars, bushes, etc. and have their reflections on the building (no clue!)

One way is to include your base reflective items in the foreground passes, set them to mattes and alpha of -1 with their original materials. This will provide you with reflections in the negative alpha space, then in the comp you can invert the alpha and be left with a reflection pass, add these in the right order over your building and the results are pretty good. The edges of the alpha can be a bit of an issue with some halos due to the inverted premultiplied edges but some alpha levels adjustments or alpha erosion can clean it up.

[Donald2B]

Thanks Eric! I am going to give that a try later this afternoon.

[Donald2B]

Okay...I am not sure what is going on, but something is still not working correctly. So I thought that I would take a file that everyone has access to. I started with the base file used in the spot3d tutorial located here: http://www.spot3d.com/vray/help/150S...rials_anim.htm

Okay so I render out my background plate which ultimately looks like this:


Then I select the 4 walls and ceiling. Go to Vray Properties and turn on Matte with a -1.0 alpha contribution. My Render now looks like the following, except that the alpha is completely black except for just the teapot object.


This is the point where I am not sure what to do...how do get the reflections to affect the alpha channel?

Thanks for everyone's continued patience. I am still waiting for the "DOH! I am such and idiot!" moment when all of this just makes sense. LOL

[Numse]

I´ve not read the entire post, so sorry if I say something stupid ;>

Anyway, I dont think there is any way to get your reflections to affect your alpha.

[Sascha Selent]

This is the point where I am not sure what to do...how do get the reflections to affect the alpha channel?

Quite simple. Do a 2nd renderpass.

Give the Teapot a fully white and selfilluminated material (so that it is flat white) and render again. Then you´ll get a mask for the teapot that is considered int the reflections too. Use this as alpha.

[Donald2B]

Okay...I have started working on this problem again. I believe I am getting all of the passes out correctly. I think the major problem is putting them all back together. Nothing I puts the reflection back on the image properly. It is almost like I need to get this pass out in order for it to work properly. Again this is the image from the Spot3D Tutorial.



Anyone have a sample flow or comp that they could show me. I am trying to prevent myself from rendering out the "black teapot" full pass in order to get the above image.

Again, thanks all for your patience. (I think this is why I am NOT a compositor!! LOL)