Computer graphics processing and selective visual display system – Display driving control circuitry – Controlling the condition of display elements
Reexamination Certificate
2002-01-17
2004-10-12
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Controlling the condition of display elements
C345S007000, C345S419000
Reexamination Certificate
active
06803928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to virtual and augmented environments and more specifically to the application of mirror beam-splitters as optical combiners in combination with table-like projection systems that are used to visualize such environments.
2. Background
Virtual Reality (VR) attempts to provide a sense of spatial presence (visual, auditory, or tactile) inside computer-generated synthetic environments to the user. Opaque head-mounted displays (HMDs) and surround-screen (spatially immersive) displays such as CAVEs, (Cruz-Neira, Sandin & DeFanti, 1993) and domed displays (Bennett, 2000) are VR devices that surround the viewer with graphics by filling a great amount of the user's field of view. To achieve this kind of immersion, however, these devices encapsulate the user from the real world, thus making it in many cases difficult or even impossible to combine them with habitual work environments.
Other, less immersive display technology is more promising to support seamless integration of VR into everyday workplaces. Table-like display devices such as Virtual Tables (Barco Inc.,
2000
a
,
2000
b
) or Responsive Workbenches (Krüger & Fröhlich, 1994; Krüger, et al., 1995) and wall-like projection systems such as e.g., Powerwalls, (Silicon Graphics, Inc., 1997) allow the user to simultaneously perceive the surrounding real world while working with a virtual environment.
UNC's “Office of the Future Vision” (Raskar, et al., 1998) is a consequent extension of this concept. Here, in contrast to embedding special display devices into the real work environment, an office is envisioned where the ceiling lights are replaced by cameras and projectors that continuously scan the office environment and project computer graphics to spatially immersive displays that could in effect be almost anything (e.g., walls, tables, cupboards) or anywhere in the office. While the cameras acquire the geometry of the office items (irregular surfaces), the rendering is modified to project graphics onto these surfaces in a way that it looks correct and undistorted to an observer. This concept can offer both, a high degree of immersion and the integration of VR into the habitual workspace.
Due to currently employed display technology, a main drawback of VR is that virtual environments cannot be optically mixed with the real world. If rear-projection systems are employed, real-world objects are always located between the observer and the projection plane, thus occluding the projected graphics and consequently the virtual environment. If front-projection is used, physical models can be augmented with graphics by seamlessly projecting directly onto the surface of those objects instead of displaying them in the viewer's visual field (Raskar, Welch & Chen, 1999; Raskar, Welch & Fuchs, 1998). However, this so-called Spatially Augmented Reality (SAR) concept is mostly limited to visualization and not suitable for advanced interaction with virtual and augmented real objects. Moreover, shadows that are cast by the physical objects or by the user, and restrictions of the display area (size, shape, and color of the surface) introduce a fundamental problem in SAR systems.
In general, Augmented Reality (AR) superimposes computer-generated graphics onto the user's view of the real world, thus, in contrast to VR, allowing virtual and real objects to coexist within the same space. Opaque HMDs that display a video-stream of the real world which is premixed with graphics, or see-through HMDs (Sutherland, 1965; Bajura, 1992) that make use of optical combiners (essentially half-silvered mirrors) are currently the two main display devices for AR. Similar to VR, the display technology that is employed for AR introduces a number of drawbacks: For currently available HMDs, display characteristics (e.g., resolution, field-of-view, focal-length, field-of-depth, etc.) and ergonomic factors usually interfere. While the resolution of both HMD types (opaque and see-through) is generally low (lower than projection-based VR display devices), today's optical see-through systems additionally lack in image brilliance, because the brightness of the displayed graphics strongly depend on the lighting conditions of the surrounding real environment. Although higher-resolution see-through HMDs do exist, e.g. Kaiser Electro-optics, Inc. (2000), they are mostly heavy and expensive, whereas more ergonomic HMDs lack in their optical properties.
Head-mounted projective displays (Parsons & Rolland, 1998; Inami, et al., 2000) or projective head-mounted displays (Kijima & Ojika, 1997) are projection-based alternatives that apply head-mounted miniature projectors instead of miniature displays. Such devices approach to combine the advantages of large projection displays with the ones of head-mounted displays. Similar to SAR, head-mounted projective displays decrease the effect of inconsistency of accommodation and convergence that is related to head-mounted displays. Both, head-mounted projective displays and projective head-mounted displays also address other problems that are related to HMDs: they provide a larger field of view without the application of additional lenses that introduce distorting arbitrations and they prevent incorrect parallax distortions caused by IPD (inter pupil distance) mismatch that occurs if HMDs are worn incorrectly (e.g. if they slip slightly from their designed position). However, as HMDs they seriously suffer from the imbalanced ratio between heavy optics (or projectors) that results in cumbersome and uncomfortable devices or ergonomic devices with a poor image quality.
Although some researchers refer to AR as a variation of VR, e.g. Azuma (1997), a strong separation between AR and VR applications does exist, which, in our opinion, is mainly caused by the technologically constrained usage of different display devices.
In this article, we introduce a prototype of a cost-effective and simple-to-realize optical extension for single-sided or multiple-sided (i.e. L-shaped) table-like projection systems. A large half-silvered mirror beam-splitter is applied to extend both viewing and interaction space beyond the projection boundaries of such devices. The beam-splitter allows a non-simultaneous extension of exclusively virtual environments and enables these VR display devices to support Augmented Reality tasks. Consequently, the presented prototype features a combination of VR and AR. Since table-like display devices can easily be integrated into habitual work-environments, the extension allows the linkage of a virtual with a real work place (e.g., a table-like projection system with a neighboring real workbench).
Compared to current HMDs, the application of a spatial projection displays (such as the prototype described here) for Augmented Reality tasks feature an improved ergonomics, a large field-of-view, a high and scalable resolution, and an easier eye accommodation (Raskar, Welch & Fuchs, 1998). In contrast to Raskar's SAR concept, however, our optical see-through approach prevents shadow casting and does not restrict the display area to the real environment's surface.
DESCRIPTION OF RELATED ART
Since the Extended Virtual Table prototype represents a combination of a table-like display and a mirror beam-splitter this section discusses previous and related works from two areas: table-like projection systems and related mirror displays.
First, we give an overview of current table-like projection technology in subsection 2.1. This is followed by a discussion on related mirror displays in section 2.2.
Table-like Projection Systems
Krüger's Responsive Workbench (Krüger & Fröhlich, 1994; Krüger, et al., 1995) is one of the pioneering table-like projection systems. The Responsive Workbench consists of a video projector that projects high-resolution stereoscopic images onto a mirror located under the table, which in turn reflects it in the direction of the table top (a ground glass screen). Analyzing the daily work situation of differ
Bimber Oliver
Encarnacao L. Miguel
Stork Andre
Chow Dennis-Doon
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung
Kumar Srilakshmi K.
Nelson Gordon E.
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