The Latest (and Maybe the First) Proposal for an Autostereoscopic Cinema Display System
An article appeared in a recent edition of the Journal of Display Technology that describes the configuration and principles of operation of an autostereoscopic display for cinema applications. The article caught my attention because it is the first time that I have publicly encountered a proposal for a system of this type.
A team led by Wallen Mphepö from National Chiao Tung University (Hsinchu, Taiwan) and colleagues from Chalmers University of Technology in Göteborg, Sweden reported their work in an article entitled "An Autostereoscopic 3D Display System Based on Prism Patterned Projection System." It is available on-line for a fee and can be found here.
The display works as follows: a video projector projects an image consisting of alternating columns of right eye and left eye perspective images. The light impacts the front surface of a screen that includes a so-called Reflective Prismatic Surface Film. The image is aligned with the prism structures and is reflected by the prisms in two directions. The angular separation between the two reflected images is designed to assure that when the viewer’s head is properly placed, the left eye sees only the left eye image and vice versa.
The researchers addressed the challenge of achieving satisfactory separation of left eye and right eye images by optimizing the prism angles as well as the curvature of the screen. An iterative process was used to derive the coordinates of the curve of the screen.
The initial result of this optimization process was an unacceptably large degree of crosstalk. In order to minimize the crosstalk, the researchers adjusted the prism angles in a way that sharpened the separation between the reflected rays. In addition, the inter-ocular separation was increased from 65 to 70 mm, and the viewing location was moved to 1.15 m, 50 mm closer to the screen. These measures succeeded in reducing crosstalk.
The authors point out, however, that it is not low crosstalk alone that makes the new 3D display innovative but, rather, the fact that this is accomplished at high optical efficiency - close to 90%. As Mphepö explained in an interview with Lisa Zyga of PhysOrg.com, image crosstalk varies inversely with optical efficiency in other autostereoscopic display technologies. This is not the case in the new configuration.
By increasing the number of prisms per pixel column, the new display can accommodate many simultaneous viewers without a consequent and extensive loss of resolution. In the illustration, a four prism per pixel column configuration is shown to produce ten 3D viewing zones in four rows.
Mphepö explained that in the prism-based design, the resolution of each individual viewer is reduced by half of the projector’s native resolution but it remains half regardless of the number of viewers added. The reason is that, rather than diving up the available pixel columns to add more views, the system increases the number of prisms per pixel column to accommodate more viewers. As an example, by using 11 prisms per incident projector pixel column, the system can accommodate 100 simultaneous autostereoscopic 3D viewers.
Mphepö foresees that the process required to fabricate the prism-based screen to be simple. If this turns out to be correct, then making an autostereoscopic cinema system should be quite feasible.
Future work by the research team will target optimizing the system for a more typical inter-ocular distance of 65 mm. The researchers also plan to increase the size of the 3D viewing zones to accommodate a greater range of head movement.
The plan is to fabricate a prototype of the current system, but the researchers have stated an interest in finding development and ultimately manufacturing partners.
By Art Berman, DisplayDaily
