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S-3D cinema is more than a passing fad, and a new era of home ...

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S-3D cinema is more than a passing fad, and a new era of home ...

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Published by
Reads 120
Language English
Document size 2 MB
In association with Sony
Working with stereo 3D
»
Stereo 3D:
the new rules
S-3D cinema is more than a passing fad,
and a new era of home entertainment is set
to follow. Mark Ramshaw looks at the fresh
challenges, the new grammar and the wider
implications for the CG industry
espite a heritage that goes as far back
as the 19th century, the popularity of
stereoscopic imagery has waxed and
waned with alarming regularity. It feels like every
resurgence is ultimately curtailed by technical
hurdles and exploitative implementation. But the last
decade has finally seen many of the barriers to
effective stereo 3D capture and comfortable viewing
overcome, and creatives as well as money men are
at last waking up to the possibilities it offers.
2010 looks certain to be a pivotal year for S-3D,
as the overwhelming success of Avatar further
galvanises an already enthusiastic film industry, and
new technologies finally bring high-quality stereo
content into our homes for the first time.
The basic principle driving stereo 3D is simple
enough: the human brain typically perceives depth
within an image on a plane, such as one projected
onto a TV or cinema screen, using cues that include
changes in pattern sizes, light and shadow, relative
motion, apparent object sizes, haze, vertical
positioning and convergence of parallel lines. Stereo
3D adds another cue – stereopsis – by supplying
slightly different projections of the same scene
to each eye. Binocular disparity (the horizontal
difference between an object in the two versions
of the scene) determines how near or far an object
is perceived to be, with the disparity decreasing for
objects positioned further away. The flat screen then
has the illusion of being a window, with elements of
the scene visible through the window and even able
to float in front of it.
Where it gets more complicated is not only
rendering or capturing good-quality stereo 3D, but
also using it in a manner that is comfortable to view
and enhances the experience. It’s not just a matter
of adding an extra camera for a live shoot or a virtual
camera for a CG scene, then hoping for the best. For
those new to the medium, it pays to learn a little
more about the new rules of S-3D content creation.
“A new grammar for stereo 3D is necessary to
avoid compromising the 3D effect and also to
produce content that is comfortable to watch,” says
Philippe Gerard, co-founder of leading French stereo
3D direction, postproduction and conversion studio
3DLIZED. “Failure to be mindful of the grammar and
the results can prove nauseous for the audience.”
There are several reasons why care is needed –
not least the fact that there are inherent challenges
that the format presents to the viewer. In the real
world, eyes turn to look at, or converge on, the
object they want to focus on. For anything up close,
a large amount of vergence is required, whereas for
something on the horizon the vergence is zero.
The floating window
Stereo 3D introduces an effect called the vergence-
accommodation conflict. (Accommodation refers to
the act of focusing the eyes.) The problem arises
because the eyes are dealing with two separate
images on a fixed screen, while the brain thinks it
needs to focus on elements in the scene as if they
were located elsewhere in space – in front of or
the screen window effectively masking a closer
object as if it was further away. The obvious answer
is to avoid such conflicts, but that’s not always easy
for artists used to 2D conventions.
One solution, explains Ben Smith, creative
director of animation studio Red Star, is a floating
window. “By creating a rectangular surround that
sits closer to the viewer than the actual screen,
you’re able to change the audience’s perception of
where the screen sits, and so give the impression
that the cropped object now sits behind it.”
The concept dates back to the mid-20th century,
but it was only since stereographer Brian Gardner
realised that it needs to shift dynamically (with the
ability to change angle as well as depth) rather than
remain static that it has become an effective tool.
Camera challenges
Camera cuts are potentially just as challenging.
When watching a 2D movie, the human eye simply
needs to switch horizontal and vertical focus when
“Effects that use the depth in front of the screen are the
most complex of all. But it cannot be done without real
care, and it needs to be well integrated into the story”
Philippe Gerard, co-founder, 3DLIZED
the shot changes. With a stereo 3D movie, there’s
refocusing on the Z plane to consider. “Whenever
there’s a switch, you need to accommodate the
time it takes for the eyes of the audience to shift
their point of focus,” says Smith. “You can carefully
plan that with an all-CG production, but it’s more
complex – you really need to previz everything.”
“We often deal with customers who want to use
stereo 3D for explosions, smoke, battles and races.
The problem is that the third dimension requires
time to be processed by the human eye,” says
Gerard. “It’s one reason why more contemplative
sequences can be the most spectacular in S-3D.
If you look at Avatar, some of the most beautiful 3D
is to be found in the more ‘poetic’ sequences.”
Spacing out cuts is obviously preferable, but
not always practical. In such instances, blending
techniques can be used to reduce the difference
in 3D space between the point of focus in the first
and second shots. It’s even possible to ramp down
from stereo to an almost mono output just prior to
the cut, then ramp the sense of depth up through
the first few frames of the next shot – all without
the audience consciously registering any trickery.
Another potential pitfall arises with stereo that
works against rather than supports the 2D cues in
a scene. Objects with negative parallax will naturally
draw the audience’s attention, for example, so it’s
often preferable to have these in focus. Because the
human eye struggles to focus on much beyond one
behind that screen. One key problem for anybody
attempting to view stereo 3D arises from the fact
that a disparity between the real and the actual
position of the image causes conflicts for objects
cropped at the edge of the screen. If the object has
been positioned to float in front of the screen, you
end up with a window violation, with the edges of
D
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Images:
Coraline © Focus Features; Alice In Wonderland © Disney Enterprises, Inc;
Avatar © 2009 20th Century Fox; Meet the Robinsons © 2007 Walt Disney Pictures