Achieving near-correct focus cues using multiple image planes
- Kurt Akeley
Typical stereo displays stimulate incorrect focus cues because the light comes from a single surface. The consequences of incorrect focus cues include discomfort, difficulty perceiving the depth of stereo images, and incorrect perception of distance. This thesis describes a prototype stereo display comprising two independent volumetric displays. Each volumetric display is implemented with three image planes, which are fixed in position relative to the viewer, and are arranged so that the retinal image is the sum of light from three different focal distances. Scene geometry is rendered separately to the two fixed-viewpoint volumetric displays, using projections that are exact for each eye. Rendering is filtered in the depth dimension such that object radiance is apportioned to the two nearest image planes, in linear proportion based on reciprocal distance. Fixed-viewpoint volumetric displays with adequate depth resolution are shown to generate nearcorrect stimulation of focus cues. Depth filtering, which is necessary to avoid visible artifacts, also improves the accuracy of the stimulus that directs changes in the focus of the eye. Specifically, the stimulus generated by depth filtering an object whose simulated distance falls between image-plane distances closely matches the stimulus that would be generated by an image plane at the desired distance. Viewers of the prototype display required substantially less time to perceive the depth of stereo images that were rendered with depth filtering to approximate correct focal distance. Fixed-viewpoint volumetric displays are shown to be a potentially practical solution for virtual reality viewing. In addition to near-correct stimulation of focus cues, and unlike more familiar autostereoscopic volumetric displays, fixed-viewpoint volumetric displays retain important qualities of 3-D projective graphics. These include correct depiction of occlusions and reflections, utilization of modern graphics processor and 2-D display technology, and implementation of realistic fields of iv view and depths of field. The design and verification of the prototype display are fully described. While not a practical solution for general-purpose viewing, the prototype is a proof of concept and a platform for ongoing vision research.