The GEOMETRY Workflow - 3D Postproduction: Stereoscopic Workflows and Techniques - page 111

exaggerated for clarity
L and/or R higher or lower
on vertical (Y) axis
Figure 4.5 Vertical Misalignment.
arch. This shape can lead to portions of the imagery appearing closer/larger
or farther/smaller than would normally be the case. In extreme forms this
can cause visual discomfort as the viewer's visual system tries to make sense
of the disparate imagery over time. This is especially troublesome when L
and R keystones each have different shapes, orientations and characteristics,
further complicating the resolution of the issue.
4.6.2.4 Solution: Correct or Duplicate
Several software tools can correct keystoning to some extent by digitally
compensating for the effect of imagers and/or mirrors. This approach works
by changing the shape of the trapezoid into a proper rectangle then crops
the rectii ed image. Another approach simply masks the areas where the
keystoning is most noticeable. What makes this a challenge is not i xing the
keystone, but i xing the keystone in both L and R in a way that does not
introduce additional artifacts due to mismatched i xes.