Virtual reality systems have become common in research labs and high technology research applications. However, this technology has yet to achieve widespread commercial use. Many if not most virtual reality systems employ specialized peripherals and display systems, like helmets, goggles, and other heads-up displays to achieve a sense of the virtual environment. Yet, there are limitations to this type of technology. Autostereoscopic (AS) technologies provide three dimensional imagery without the need for goggles or other viewing aids.
Advances in virtual reality systems, including AS technologies, may provide for greater commercial acceptance. For example, lenticular screens and parallax barrier strip displays are dominant and popular AS technologies. Lenticular and barrier strip AS systems are known, with commercial products presently available. An example of a known AS system is the “Varrier” system introduced in 2004 by the Electronic Visualization Laboratory (EVL) at the University of Illinois at Chicago (UIC).
The function of a parallax barrier is to occlude certain regions of an image from each of the two eyes, while permitting other regions to be visible, as generally illustrated by FIG. 1. A first screen 2 includes a plurality of transparent strips 4 interspersed with a plurality of opaque strips 6 to selectively transmit/occlude corresponding image planes 8 from a second screen 10 to each of a right and left eye 12 and 14. By simultaneously rendering strips of a left eye image into the regions visible by the left eye and likewise for the right eye, a complete perspective view is directed into each eye. A user perceives a 3D representation, and an AS experience results without the need for 3D glasses. When the barrier strip concept is coupled with real-time viewupdate, head-tracking, first-person perspective, and interactive application control, an AS VR system results. Such systems can be presented on a large scale (e.g., a grid of multiple tiled screens, a smaller scale (e.g., a desktop), or any other scale.
A known parallax barrier is a high-resolution printed film that is affixed to a glass substrate and appended to the front of an LCD monitor. Another known variation is a lenticular screen which functions equivalently. The printed pattern on the barrier is a fine-pitch sequence of opaque and transparent strips, with the period of the repeating pattern on the order of 0.5 to 1 mm.
The period of this barrier is determined a priori by the system designer and determines key outputs in system response that cannot be varied once built. Output parameters such as view distance operating range (minimum, maximum, optimum), visual acuity, and the fact that the system is capable of only supporting one user at a time are three such results of barrier period choice. The consequences of these design-time decisions are magnified by the long turn-around time to correct or modify the barrier.
Moreover, with respect to supporting two tracked users, there is no single optimal barrier period that can be pre-selected since the barrier period causes inter-channel conflicts between users. In addition to fixed working range and strict single user mode for tracked two-view systems, static barrier AS systems have some other disadvantages. One is that the barrier cannot be disabled—it is essentially “locked” in 3D mode and not able to provide 2D imaging. Another problem relates to horizontal resolution loss. One barrier period consists of a duty cycle of approximately ¾ black to ¼ clear. Hence, each eye channel contains only ¼ of the horizontal screen resolution.
The spatial inefficiency of parallax barrier AS is a direct result of the Nyquist Sampling Theorem, which dictates that eye channels are separated by equivalent amounts of unused screen space, termed “guard bands.” Also, head-tracked static barrier AS is further limited by the fact that performance criteria such as frame rate and latency are more critical in fixed barrier AS than in other stereo techniques. Unlike passive and active stereo VR, moving the head faster than the system response time results not only in scene lag but also in visible artifacts because incorrect data is steered to the eyes. Since channels are continuously steered to the user's eyes in head-tracked AS, one may readily out-run the system and move the head faster than channels can be updated. Defects such as image flicker, black banding, and ghosting are visible in a head-tracked AS VR system during head movements, and disappear when the user stops moving.