<nettime> Do-It-Yourself Stereoscopic Video

[_manu Luksch <manu@ambienttv.net>]

Limitations Permitted: Notes on DIY 3D stereoscopic video
http://www.ambienttv.net/content/?q=limitationspermitted

For Limitations Permitted, Manu Luksch was filming in British Sign Language
(BSL), which encodes meaning in three dimensions of space (as well as time).
The signing is filmed in 3D (stereoscopic) video in order to allow full
expression of the language. For concept outline, pls visit the project
website. Following text shares the experience of developing a low-budget DIY
solution for working with 3D stereoscopic video.


THE 3D VIEWER
The videos are presented for individual viewing in a hand-held viewer, which
is designed to run on batteries for 8 hours. Off-the-shelf 3D head-mounted
displays were either too low in resolution or too expensive. Engineering a
custom solution with miniature LCD screens and a file player would have been
ideal, but we needed a working prototype very quickly, so we decided to
modify a pre-existing portable video playback device, mounting it behind a
pair of eyepieces. 
Binocular eyepieces present a magnified image to each eye at a comfortable
viewing distance, rather like a ViewMaster. The left and right images can be
presented independently to each eye (on two screens, or side-by-side on a
larger screen), or can be encoded as a single image on one screen. We
initially considered using a pair of devices with small VGA (640 x 480)
displays, but managing the synchronised playback of the files under their
closed operating system was not an inviting task. We were left with the
single-screen option, but sourcing a device that had a high resolution
screen of the required size and long battery life was difficult. Eventually
we found a PMP (personal media player) with a 4.3" 800 x 480 LCD display,
with a fine-enough pixel-pitch to present a smooth and sharp image through
the pair of eyepieces. With an auxiliary battery, continuous playback time
exceeding 8 hours was possible.
In the viewer, the 3D information could only be encoded into a single image
using the anaglyph technique (using red and cyan filters) ­ most LCD screens
do not refresh quickly enough to work with shutterglasses and other
polarisation-based techniques. However, even with high-quality filters,
there was considerable ghosting and smearing of the image. The remaining
option was to place scaled-down left and right images next to each other on
the screen, and separating the left and right optical paths with a plastic
mask. This gave each eye a lower-resolution image, 400 pixels wide, but in
full colour and with no interference between the left and right eyes.

RECORDING IN 3D
For encoding the 3D information, we initially considered using a prismatic
camcorder attachment that allows left and right eye-views to be recorded to
alternate fields of interlaced video. Only one camera is required, though
the vertical resolution of the image is halved, and there are also
limitations on the recoding format (MPEG-2 based formats such as HDV do not
work). The other option was to use a pair of camcorders mounted about
eyes'-width apart, running in synchrony. Research suggested that an
(expensive) external device would be needed to keep the cameras in sync, or
at least to indicate when they drifted out of sync. However, results of an
experiment with a pair of (unmatched) miniDV camcorders, started together
manually, looked promising when viewed in the prototype viewer. It became
clear that the critical factor was not sub-frame synchrony between the
cameras, but lens alignment and matching of perspectives. When a neighbour
donated an old camcorder to us, we had access to two camcorders with
identical lenses (Sony PD-100 and an TRV-900). These were mounted parallel
and as close as possible on a bar, levelled with a spirit level, with the
lenses zoomed to the wide stop. (The camcorders' width meant that the lens
separation was a little greater than average human eye separation, which
exaggerated the stereoscopic effect slightly.) Both camcorder transports
could be controlled with a single remote control ­ giving us an inexpensive
but very effective standard-definition 3D shooting rig.

[written by Mukul 2009/06/07]

Limitations Permitted
Site-specific mixed media installation by Manu Luksch, Neal White and FLIX:
the fourth Peckham Space commission.
Peckham Square, London SE15
21-28 June 2009, 10am-6pm, free
http://www.ambienttv.net/content/?q=limitationspermitted
http://www.peckhamspace.com







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