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Space Perception. Depth Cues Tasks Shape-from-Shading. Perception of surface shape. Simple lighting model Light from above and at infinity Specular, Diffuse and Ambient components Oriented texture can enhance shape perception. Lighting model. Lambertian, specular, ambient + cast shadows.
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Space Perception • Depth Cues • Tasks • Shape-from-Shading
Perception of surface shape • Simple lighting model • Light from above and at infinity • Specular, Diffuse and Ambient components • Oriented texture can enhance shape perception
Lighting model Lambertian, specular, ambient + cast shadows
Standard lighting model Ambient illumination Specular refection diffuse reflection = lambertian
Shading Specular reveals fine detail
Lighting • Simple lighting model • Not photorealistic • Single light source from above and at infinity • Specular for detail • Cast shadows if scene is simple
The 3D vs 2D debate • Should we display abstract data in 3D? • Depth cue theory • Depth cues are environmental information that tell us about space • Can be applied somewhat independently
Perspective (Cockburn andMcKenzie) Perspective Picture plane position Occlusion Picture plane position Occlusion
Atmospheric perspective Reduce contrast with distance “depth cueing” in CG
Stereopsis • Based on disparities • A super acuity • Only good near point of fixation • Poor for large differences • Double imaging possible for 1/10th deg.
Relative Importance , 96 Motion parallax 0.001 Occlusion Height in field 0.01 Relative size Depth Contrast 0.1 Binocular disparity Convergence accommodation 1.0 Aerial 1 10 100 Depth (meters) Cutting, 1996
3D options Vergence Focus Motion Parallax Stereopsis Shape-from Shading or Texture Perspective Occlusion
Yes of course 3D can give us moreBut only if it supports some task • Locomotion • Heading, occlusion • Understanding the shape of surfaces • Shading, texture, stereo, motion • Tracing paths in graphs • motion stereo • Local reaching • stereo – convergence
Relative position • For fine judgments - threading a needle stereo is important +shadows, occlusion • For large scale judgments, perspective, motion parallax, linear perspective are all important. Stereo is not important
Stereo +60% Motion +130% Stereo + Motion +200%
How to generateMotion? • Passive rotation • Hand coupled rotation • Head-coupled rotation • Time has does not vary much
Stereo Display Requirements • 3D GIS data • Comfortable stereo display • Many orders of magnitude • Better than normal stereopsis
We Know That • Vergence and focus conflict • Stereo perception is plastic (Wallack) • Can be rapidly recalibrated (Judge and Miles) • There is a synergy with motion parallax • Occlusion is a strong cue to depth
Cyclopean Scale Helps with • Vergence focus conflict • Diplopia • Disparity scaling • Frame cancellation • It works dynamically? • Change the virtual eye separation
Understanding surface shape Victoria Interrante
Norman, Todd & Phillips Note: Random textures on surfaces Stereo and motion roughly equal Note large angular error ~ 20 degrees Observation: Stereopsis is a super-acuity and relies on fine texture disparity gradients
Space perception depends on the task Occlusion the most important depth cue – consider that windows rely on it Perspective may not add anything by itself Stereo important for close interaction Motion important for 3D layout Shape-from shading and texture important for surface perception (but non photorealist) Conclusion – 3D is better but only it adds something
Stereo technologies • Frame-sequential (shutter glasses) • Polaroids • Mirror stereoscope • HMDs • Color anaglyphs • Chromadepth • Holograms
Stereo shutter glasses Alternate right and left eye images on monitor. Syncronized shutters block right and left eyes in alternation Monitor: 120 Hz R,L eyes 60 Hz each Problems: ghosting due to slow Phosphor decay. Lower resolution CRT displays only Expensive glasses
Polaroids Silver screen Preserves polarization R L Problems: ghosting Advantages: Cheap glasses
Anaglyphs Problems: Ghosting Inability to use color
Works with LCD displays Lenticular To Right Eye To Left Eye The display uses cylindrical Prisms in vertical columns What is wrong with this picture? Problems: reduced resolution, limited head position. Theoretical limits on resolution