P3D Toy Story --> 3-D

[Tom Deering <tmd@xxxxxxxxxxx>]

>It is not always as easy as you might think to make a
>cg film into a stereo film.  There are many tricks
>that we use to speed up production such as flat
>paintings for backgrounds, and many other tricks that
>would need to be pulled out and re-worked if a stereo
>version was needed.

I am working on a seminar on this topic right now for a company that 
sells a 3-D rendering package.  There are a couple things that CG 
artists do that appear to be three-dimensional, but are actually 
two-dimensional.  We don't get caught because our work is usually 
shown in 2D, but if you stuck in a second virtual camera and made a 
stereo pair, the effect would be exposed.

1. Forced perspective.  Sometimes it's easier to make things look 
distant by just making them smaller.  Other times we draw things 
warped to mimic the effects of perspective.  A road that disappears 
into the distance might be drawn so it gets narrower rather than 
realistically parallel.  This might not work in true 3-D.

2. "Shaded" surfaces.  Sometimes completely flat objects are drawn 
with surfaces that mimic textured surfaces.  Depending how close 
these surfaces are, actual 3-D would give away the trick.  For 
instance, a brick wall with realistic grout and texture in 2-D might 
look flat as glass in 3-D.

3. I often speed the process by rendering complex but non-moving 
objects just once.  Then I place this flat picture into my model.  If 
I have a forest, I render all those trees one time, then place this 
picture of the forest in the background.  Won't work if you show the 
scene in stereo, it will look like a flat picture of trees.

If you know your model will be viewed in 3-D, you can avoid these 
problems.  But movies that were not designed for 3-D, like Toy Story, 
will be full of them.

If they wanted, they could rework certain scenes.  That's exactly 
what they did when they converted A Bug's life from wide-screen 
format to 4:3 television format.  At times they moved objects closer 
together and rendered them again so they would fit on the smaller 
screen.  Other times they rendered completely new material to fill in 
at the top and bottom.

Tom Deering
(Someone with my name appears in the credits of A Bug's Life and Toy 
Story 2.  Lucky guy.)
---
tmd@xxxxxxxxxxx    http://www.deering.org

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