Graphics Reference
In-Depth Information
5.7 Real-Life 3D Post: DEPTH by Juan I. Cabrera
5.7.1 Overview
Depth can be interpreted in two ways:
1. The amount of depth in a shot (maximum distance between objects or
disparity between eyes in the shot).
2. The depth (or convergence) point at which we want our shot to be.
Usually we cannot do much to change the i rst one unless we use advanced
postproduction tools. But we need to account for this disparity when we are
working on the second (convergence). Think about it as having a shoe-box
on top of a line drawn on the table. The line would be your screen. The
length of the box is depth as in the i rst dei nition. Now, if you move the
box forward or backward with respect to the line, then you are changing
the object's global depth, as in the second dei nition. Now imagine there
was a limit as to how far away you can move your box. Then the length
of your box will have great inl uence on how far you can push it. As it
happens, 3D works exactly like that.
5.7.2 Good Depth Requires Good Geometry
A successful depth grade requires that shots already have good geometry. If
the geometry is wrong, it is almost impossible to achieve a viewable result
by just changing depth. Having said that, if our geometry is correct, we can
have a lot of fun playing with depth.
Second, remember that when you are depth-grading you are moving one or
both of the eyes horizontally, that will create a gap on one of the sides. There
are several ways to approach this, you could scale both eyes to compensate
for it (but it will increase your disparity). Or you could work at a greater
resolution than your i nal delivery and have an overhead of pixels you can
use for convergence. One way or the other, you must make a decision if
you don't want the edge of your image to move around from one shot to
the next. (I have seen this problem in productions with way more budget
that you would imagine.) Also, remember you can apply the transformation
to one of the eyes or both eyes, depending of your needs. Sometimes one
of the eyes is left completely untouched so it can later be used for the 2D
version of the show.
 
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