The GEOMETRY Workflow - 3D Postproduction: Stereoscopic Workflows and Techniques - page 110

Common temporal geometry issues include:
• Shutter Angle Mismatch
• Phase Mismatch
Please note that illustrations of geometry issues in this chapter are exaggerated.
Most issues are much more subtle than they are portrayed in the illustrations.
“The most common issues I am faced with in post include alignment
errors in terms of the mechanical placement of cameras and lenses
on a rig. The other has to do with the inherent properties of
light passing through glass or rel ecting off mirrors. The hardest
thing to i x is a i eld of view (focal length) mismatch, because the
mathematics involved with trying to undo i eld of view differences
are very challenging. Color tools are so good that I do not worry
about i xing most color issues.”
—Matt Blute
4.6.2.1 Issue: Vertical Alignment Mismatch
This issue occurs when L or R is higher or lower on the vertical Y-axis
relative to the other (Figure 4.5) . Typically this situation occurs because
of incorrect settings and/or miscalibration of the production imaging
system. Over time this issue can lead to audience discomfort and/
or discontinuity. Teams can also inadvertently introduce issues in post
through misapplication of tools and techniques. Provided version control
is reliable, teams should be able to reverse mismatches introduced in post
once these mismatches are spotted.
4.6.2.2 Solution: Correct the Verticals
Move L and/or R along the Y-axis (i.e., up and/or down) until similar points
in L and R are at the same vertical position.
4.6.2.3 Issue: Keystoning
Keystoning is the effect that occurs with both parallel and converged shooting
formats (Figure 4.6) . It is a natural result of optics and not at all mysterious.
In many cases, keystoning is not even noticeable. The resulting trapezoidal
shape of an image recalls the shape of the keystone at the apex of a stone