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  • December 2013

Optics InfoBase > Spotlight on Optics > Multi-view autostereoscopic projection display using rotating screen

Multi-view autostereoscopic projection display using rotating screen

Published in Optics Express, Vol. 21 Issue 23, pp.29043-29054 (2013)
by Osman Eldes, Kaan Akşit, and Hakan Urey

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Spotlight summary: For over a century, displays like the parallax barrier and lenticular screen have offered 3D autostereoscopic (i.e., glasses-free) images to a stationary viewer. However, presenting a well-corrected, high-resolution 3D picture across a wide viewing area remains a significant challenge that has impeded the advance of glasses-free display technology in the consumer market. Two primary obstacles prevent the realization of a true “walk-around” 3D display, like the one many of us remember from the film Star Wars. First is data-throughput: many images, each showing the 3D scene from a slightly different viewpoint, are often required to ensure a pleasant glasses-free viewing experience. Whether this extra “multi-view” information is accounted for by spreading it across space (e.g., within an array of projectors) or across time (e.g., on one very fast-flickering screen), the spatial resolution or temporal smoothness of the presented 3D imagery is inevitably sacrificed. Second, it is challenging to construct a display that guarantees the perceptual quality of its 3D content throughout a large viewing volume. The presented multi-view imagery often only exhibits minimal cross-talk within a narrow viewing angle and across a short viewing distance range.

A special class of autostereoscopic 3D display aims to sidestep these two challenges by including a head-tracking device, which precisely measures the position of a viewer’s eyes as he or she moves around the image. This information can help guide where the display projects its multi-view content. Most head-tracking displays only need to present a viewer with two images – one unique image to each eye, just like 3D displays that rely upon glasses. This simplification greatly reduces the demands of high data throughput, to just twice what a conventional 2D display requires. What’s more, the ability to guide the projected 3D imagery to a moving viewer often enables a much larger viewing volume than non-tracking 3D displays. However, tracking comes with an inevitable increase to display complexity, with the most significant challenges arising from the introduction of mechanically moving components.

In this paper, Eldes et al. demonstrate a simple and robust head-tracking 3D display that enables glasses-free viewing with a minimal amount of display movement. The proposed system consists of two projectors positioned near the viewer. The projectors focus their images onto a rotating, retro-reflective screen. Each projector illuminates the screen with one stereoscopic image at a unique angle, which is then retro-reflected along a similar angle to enter only one of the viewer’s eyes. The geometry of the proposed setup enables the reflected angle of each image to be varied simply by rotating the retro-reflective screen to a new orientation. Thus, as the viewer’s head moves around, the retro-reflective screen simply reorients itself to ensure the two projected images, taking the form of two bright stripes, correctly meet both eyes without overlapping.

A large benefit of the proposed 3D display setup lies in its mechanical simplicity. Only one relatively slow rotating servomotor is needed to guide the stereoscopic image content across the three-dimensional viewing volume, while other head-tracking displays often require at least two separate mechanisms of mechanical motion. What’s more, many prior setups have had difficulty following a user’s eyes along the axis perpendicular to the display screen, which the proposed display’s “stripe” projection style can take into account quite easily. The paper thoroughly analyzes image brightness and cross-talk as a function of viewer position, and demonstrates that an acceptable image is viewed through up to 70 cm of lateral movement and 50 cm of movement perpendicular to the screen, representing a sizable and comfortable viewing volume.

One current downside of the proposed setup, as shared by many other head-tracking systems, is its ability to accommodate only one viewer. However, there are a number of possible extensions that may help address this limitation. First, there is no reason why this technique need be limited to only two projectors. Furthermore, multiple perspectives could be quickly sequenced over time, as other 3D display methods (e.g., glasses-based displays) take advantage of. Such extensions could also help the current setup incorporate real movement parallax, instead of just stereo parallax, into its display repertoire. Although the dream of a true walk-around 3D display may still be quite far off, Eldes et al.’s system is a simple and robust way to allow one viewer a good amount of movement during a pleasant 3D viewing experience.

--Roarke Horstmeyer

Technical Division: Optoelectronics
ToC Category: Optical Devices
OCIS Codes: (120.2040) Instrumentation, measurement, and metrology : Displays
(230.1980) Optical devices : Diffusers
(330.1400) Vision, color, and visual optics : Vision - binocular and stereopsis

Posted on December 10, 2013

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