Multi-viewer Tabletop Autostereoscopic Display
The paper mentions a novel and practical Auto stereoscopic tabletop displays which would provide stereo perception to multiple users without special glasses. The main challenge is to provide multiple stereo viewpoints to different users at the same time through the same interface. Existing auto stereo display technologies mostly fall under three categories – holographic, volumetric and parallax based. Volumetric displays do not support occlusion, which has been recently handled through spinning anisotropic mirror for surround distinct views but it does offer multi user parallax along horizontal directions.
Parallax-based displays using lenticular lens have been fairly efficient in auto stereo displays. It divides the display surface spatially into multiple holes/slits as barriers through which light passes. The sheet transmits more light leading to brighter display but at expense of focus degradation. Parallax displays need head tracking to support dynamic view positions and work only in fixed horizontal direction, making them unsuitable for tabletop surfaces.
The RHD or ‘Random Hole Display’ system mentioned in the paper consists of a high density LCD display panel with very large horizontal and vertical viewing angles. The random holes barrier is a dense pattern of tiny placed holes, printed on a thin polyester film at 2500 dpi and attached to the display surface. It also uses an optical tracking system for user tracking and geometric calibration. Based on the hole density, each user sees a different subset of native underlying pixels depending on the position. A lower one leads to less conflicts between pixels viewed by different users but also lowers the quality of display due to lower effective resolution and brightness. With increase in conflicts i.e. increase in number of viewers, quality of the view rendered decreases. A pseudo-random Poisson distribution of the hole pattern is used to distribute view conflicts across the entire display. The system incorporates a hardware accelerated four pass rendering algorithm, wherein a visibility mask is generated for each view, all masked images are combined and the error is diffused to visible neighboring pixels for each view.
RHD is a promising system which allows multi-user applications interacting with same virtual objects in real time without need of special glasses/equipment.
SCAPE
Scape is a system aimed towards multi-user collaboration in a virtual environment setup. Users use the same physical setup for interaction through individual perspective or field of view, along with support for physical and interpersonal interactions. The core display component for Scape is Head Mounted Projective Display (HMPD). HMPD uses projective lenses and renders effective 3D visualizations with large Field of View and supports correct occlusion of virtual objects by real objects.
Another important characteristic of the physical space in Scape is retro reflective surface which projects light exactly in opposite direction but only works for limited angles. The systems consist of four walled room sized virtual environment (providing immersive experience) with an interactive workbench wherein multiple users with HMPD’s can simultaneously view and interact with 3D view of a physical object (which could be retro-reflective). Each user has its own independent perspective and based on systems computational and display prowess, as many HMPDs can be introduced. The paper also talks about the Software associated which is a cross platform, extensible toolkit – Scape.
Collaboration is an interesting area of research in Virtual environments but poses a lot of practical challenges – multiple user tracking and calibration, lighting and conflicts between different user’s interactions.