9
Watching the Edges
When composing films for smaller screens, filmmakers must take into account the
prospect that objects with strong negative parallax (i.e. objects that intrude a significant
distance into the viewer’s space) may be truncated at the right or left sides of the screen,
confusing the signals that viewers need in order to accurately place the objects in space.
To correct this
edge violation
effect, movable mattes (or
floating windows
) may be
applied in post, temporarily masking objects that reside too long at the sides of the frame.
However, whenever possible, 3D filmmakers are well advised to compose their scenes so
that objects with strong negative parallax are not allowed to linger for more than a second
or two at the right and left sides of the frame.
Minimizing Disparities
To achieve effective 3D, every possible disparity between the images captured by the right
and left lenses of the cameras must be minimized—with the obvious exception of the
distint point-of-view of the two lenses. Accomplishing this goal requires maintaining
precise synchronization between the cameras in addition to achieving a precise match
between the optics of the lenses and a precise match between the imaging systems in the
cameras. Mismatches in sync or in optics, as well as stray reflections, light flares, or stray
objects in the frame—essentially any artifact introduced during production or post that
affects one “eye” but not the other—can induce
retinal rivalry
—a conflict between the
components of the stereo pair that disrupts the web of illusions that produce effective 3D.
Filming Live Events
When shooting live events such as stage performances and spectator sports, 3D
filmmakers confront several limitations that can compromise their ability to capture
effective 3D. Foremost among these are the need to make all of the decisions regarding
I/O and convergence in real time plus the restriction upon the placement and motion of
the cameras. The first limitation can be
addressed by a stereographer who has access
to 3D feeds from the cameras and can relay
I/O and convergence decisions to camera
assistants who can quickly adjust the I/O
and convergence of the cameras. But since
effective 3D places the viewer
inside
the
action of the film, as an active participant
and not merely as a passive spectator, the
second limitation is more difficult to address.
While live performances generally permit
cameras to have a limited presence on the
stage, spectator sports typically place strict
limits on the space in which cameras can
operate. Unfortunately, this space is outside
the space of the key action in the game.
Fig.8 – Live Event Spaces
As a result of these limitations, 3D filmmakers who wish to effectively capture live events
may need to depend upon the deployment of yet-to-be-invented robocams—remote-
controlled 3D cameras that can unobtrusively dip in and out of the subject space without
interfering with the freedom of movement of the performers or the players and at the