Saturday, 5 November 2011

Shadows and Environmental Reflections

So, after creating a virtual environment from a live action plate I thought I'd take a look at what it was possible to achieve within this environment.
Unfortunately for this exercise when I rendered the scene out it soon became obvious that the 3D track was not up to par and as such the geometry I placed into the scene slipped and jumped about the place, thus making the whole shot look like pure arse.
This was a bit of a shame because all the work up to then looked promising. This however is another good lesson to learn and just re-enforces the practice of getting things right at the input, or initial stage of production. That age old allegory; "you can't polish a dog turd" still holds true today and is something I will be especially mindful of when it comes to producing the money shots.

So, as the sequence looked rubbish that doesn't mean that the still frames looked bad, so here's a little look at what I did.

Back at the old location again, I decided in true 3D CG style to put a sphere right in the middle of the scene. Why I hear you ask? Because I can. But, this isn't just any sphere, this is a sphere with a true to life shadow and environmental reflections!

If you saw my previous blog entry on 3D environments, you'll soon notice that from this match moved footage I recreated this environment within Maya. As this environment very closely matched the actual physical space and the camera move was (roughly) taken from the physical camera, it allowed me to use a technique known as Camera Projection to map the reflections onto the sphere. Here's how it works:

This mash of a rendering above is the geometry of the match modelled space, however instead of texturing this space with UV co-ordinates, I duplicated the 3D match-moved camera, movement, translation and all and used this second identical camera as a sort of film projector if you will. This projection camera projected the original footage that I filmed back onto the blank 3D geometry (which you can see above), thus creating perfectly matched reflections for the sphere to pick up on. Once this was achieved it was just a matter of rendering all the elements out separately for comp.
This is done via the Maya render layers where it is possible in render to turn off the primary visibility of geometry but still have it picked up in reflections.

This image is an example of that, as all the other geometry has had it's primary visibility disabled but is still casting reflections.
The final element in this shot was the shadow which again, was rendered in the same way. Using the 3D geo to help with the shadow, I rendered out a simple shadow pass on the alpha channel for use in comp.

So there you have it. All the elements of placing 3D geo into a match moved scene. There were a few final touches such as a colour and grade correction and a defocus on the ball to fit it in the scene but I'll cover them properly down the line. And maybe next time I can get track to work so there's some proper footage to look at!

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