Masking / g-buffer question.

[Tommy L]

Hello all, a little puzzler:

The attached image is a still from an animation. I would like to render the cars seperately (from a different file) but would like them to go behind the trees and lamposts that are outlined on the image.

 

I know one way of doing it, but that requires rendering the trees from a seperate file, can I not asign the foreground trees to a seperate (alpha(?))channel in max? Which g-buffer channel will do this?

 

I am rendering in max/v-ray and compiling in aftereffects6.5.

 

Manythanks,

Tom.

[NeonMojo]

You can do this several ways... one way would be to render out to rpf and make sure you check the material ID or object ID check box. That would give you the ability in after effects to isolate by material or object depending on your settings for the rpf.

 

Another way would be to use vrays matte object settings and do the cars as a separate pass.

 

Personally, I like using rpfs but file size can become large especially when doing animations. Also a separate pass makes it more difficult to get the cars to show up in the building reflections...just keep that in mind as well.

 

Good luck

[Tommy L]

Thanks Matt. I thought the only option like that was .RLA which is not supported in AE or PS (just combustion i think?)

Ill try it.

Tom.

[Tommy L]

I found this in the AE help:

Though After Effects can import third-party files with depth information such as ElectricImage (.eiz) files and .rla file formats, and interpret the z-space channel in those files, it cannot animate individual objects within those files. After Effects treats composited third-party 3D files as a single layer. That layer, as a whole, can be given 3D attributes and treated like any After Effects 3D layer, but the objects contained within that 3D file cannot be manipulated individually. To access the 3D depth information in these files, use the 3D Channel effects (see the After Effects Help).

 

So i dont think i can isolate by object id (for example) and use as a mask template using an rla or rpf. I was hoping i could render a seperate pass using the g-buffer in vray which could distinguish between id's.

 

Any help much apreciated.

 

Tom.

[JamesTaylor]

Tom you should be able to do it using after effects, although it may take more than 2 passes. (you'll need 3 layers in total - background, cars & foreground)

 

AE will bring .rpf files, i've used them recently.

 

if you render your main image out without the foreground elements of the trees and lamp posts you can use that as backdrop layer. 2nd layer will then be your cars, rendered from separate file and finally render your foreground elements as your top layer. Since the cars are below the foreground layer they'll pass behind the foreground elements.

 

If you use the object ID or Material IDs and .RPF you should be able to generate appropiate masks to isolate the background and foreground elements from the 1 render.

 

I'm sure its possible but may take a little playing around with samples 1st to get your head round it all

 

Looking forward to seeing this one complete, as are a few others too i think!

 

James

[anthony cortez]

You could try this masking technique:

 

First, Go ahead and render your cars out in its own file.

 

Next, you'll have to merge those cars into the rest of the scene environment. Make a selection set just for the cars.

Open up the render dialogue window, and under Render Elements tab, add a Matte Element. Scroll down and set the output path where you want the mask to be saved.

 

Scroll down to Matte Texture Element and check on 'Include' and then add the Selection Set for the cars you had made earlier.

 

Press render and it should start rendering out a matte of just the cars being occluded within your environment. You can now use this matte as Luma Matte in Aftereffects.

 

Like Neon said earlier, you won't be able to get the reflections to show on t the buildings unless you render out a seperate reflection pass as well.

 

Hope this helps.

[Tommy L]

James,

Thanks, that is the method i know how to do. I was hoping i could cut out one of the passes (foreground) by using the material or object ID in the render to copy the foreground objects in the render to a new layer (top layer) in AE. Esentially, as the background is not goin to change after rendering, I want the trees and lamposts to be the alpha channel instaed of the background. Surely this is possible?

 

Anthony,

I dont understand how your method puts an accurate foreground in fronbt of the cars?

[anthony cortez]

Here's a breakdown from one of my scenes that has similar elements...the fourth image is what you get when you use the Matte Render Element in max. Using all the objects in your scene, it simply masks out whatever you add to your selection set, in this case, the cars + road.

[Tommy L]

Thanks Anthony, I get it now. That will be very useful. The matte has to be made in scanline right?

[anthony cortez]

NP, could be done in mr as well. good luck!

 

OT: My 31st post on my 31st Birthday, on 1/31!

[Tommy L]

Just happens the test render isnt at a place with a tree in front, but the work is comeing on well.

 

PS, I guess this could be moved to the WIP section as ive overcome the problem?

Cheers,

Tom.

[anthony cortez]

Lookin good so far! Reminds me of this racing game for the xbox called Burnout

[dinhtuan]

Very good way Anthony. Thank U