|
|
spi home
people projects
publications
|
gallery
courses
internal
demos media
lab home |
|
|
The Spatial Imaging group at the MIT Media Lab developed new technology and interfaces for holographic and other spatial displays. It was directed by Stephen Benton, who passed away November 9, 2003. Work on electronic capture and display of 3-D images has continued as a part of the work of the Media Lab's Object-Based Media group.
Holographic
stereograms are generated from precomputed
fringe elements and a set of rendered or optically-captured parallax views
of a scene.
|
|
|
|
|
|
|
|
An
idealized horizontal-parallax-only (HPO) stereogram, shown at the
left, would reconstruct continuous parallax in the horizontal direction.
Each holographic stereogram "pixel" would project the
same information that a "live" scene would, to a viewer
in any part of the viewzone.
|
|
|
|
|
 |
Since
we can't actually encode infinite parallax, scene parallax is captured
from a finite set of directions, and is then re-projected back in
those same capture-directions. In order to prevent gaps between
parallax views in the viewzone, each view is uniformly horizontally
diffused over a small angular extent.
|
|
|
|
|
 |
Two
things are needed to generate a holographic stereogram in this fashion:
a set of N images that describe scene parallax, and a diffraction
pattern that relays them in N different directions as described
above. First, we compute a set of N diffractive elements called
basis fringes. When illuminated, these fringes redirect light into
the viewzone as shown at the left. These diffractive elements are
independent of any image information, but when one is combined with
an image pixel value, it directs that pixel information to a designated
span in the viewzone.
|
|
|
|
|
 |
To
capture or render scene parallax information, cameras are positioned
along a linear track, with the view normal also normal to the capture
plane. N views are generated from locations along the track that
correspond with center output directions of the basis fringes. In
this type of HPO computed stereogram, correct capture cameras employ
a hybrid projection -- perspective in the vertical direction and
orthographic in the horizontal. Conventional perspective views will
lead to slight distortion in the reconstructed images.
|
|
|
|
|
 |
Once
N parallax views have been generated, they are combined with the
N pre-computed basis fringes to assemble a holographic stereogram.
(The same basis fringes can be used for any sweep of parallax
views generated with the same capture geometry.)
Each holo-pixel is computed as a sum of basis fringes scaled by
corresponding image pixel values as shown at the left. The resulting
holo-pixel sends N different image pixels in N different directions,
when properly illuminated.
|
|
|
|
|
 |
What
results is a kind of light-field reconstruction of the captured
scene. The pixels of each parallax view are projected in the same
direction from which they were captured, and uniformly spread a
little to prevent dead space in the viewzone. When a viewer observes
the reconstructed image, sampled scene parallax information is relayed
to each eye, and this stereo view changes appropriately and smoothly
with side-to-side head movement. Since the display has no vertical
parallax, distortion-free viewing is available only at the correct
viewing distance, as shown to the left.
|
|
|
|
|
SELECTED
REFERENCES:
Mark
Lucente, "Diffraction-Specific
Fringe Computation for Electro-Holography", Ph.D. Thesis,
Dept. of Electrical Engineering and Computer Science, Massachusetts
Institute of Technology, September 1994.
Michael
Halle, "The
Generalized Holographic Stereogram", S.M. Thesis, Program
in Media Arts and Sciences, Massachusetts Institute of Technology,
February 1991.
Ravikanth
S. Pappu, et. al., "A
generalized pipeline for preview and rendering of synthetic holograms,"
Proceedings of the IS&T/SPIE's Symposium on Electronic Imaging,
S.A. Benton, ed., Practical Holography XI, February 1997.
Mark
Lucente and Tinsley Galyean, "Rendering
Interactive Holographic Images" Proceedings of SIGGRAPH
'95 (Los Angeles, CA, Aug. 6-11, 1995), pp. 387-394.
J.
A. Watlington, Mark Lucente, C. J. Sparrell, V. M. Bove, I. Tamitani.
"A
hardware architecture for rapid generation of electro-holographic
fringe patterns" SPIE Proc. Vol. #2406: Practical Holography
IX, 2406-23, (SPIE, Bellingham, WA, 1995).
Other
references located on our publications page...
|
|
 |
 |
 |
 |