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Depth Perception & 3D Vision

Depth Perception & 3D Vision. Reza Rajimehr. 3-D Perception: Inferential leap from image to environment. Inverse Problem: depth ambiguity. No inverse problem with 3-D retina. Reducing the problem. Perceiving distance. Depth Surface orientation: Slant and Tilt. Perceiving 3-D objects.

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Depth Perception & 3D Vision

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  1. Depth Perception & 3D Vision Reza Rajimehr

  2. 3-D Perception: Inferential leap from image to environment Inverse Problem: depth ambiguity No inverse problem with 3-D retina

  3. Reducing the problem Perceiving distance • Depth • Surface orientation: Slant and Tilt Perceiving 3-D objects

  4. Surface layout: recovering orientation at a distance Visible surfaces

  5. Theoretical Frameworks For solving the inverse problem

  6. Ecological optics • Active exploration of the environment (ecology) • Information available in the optic flow is sufficient for the perception (direct perception), no need for internal representations • Adding temporal dimension to the 2-D optic array (dynamic optic array) could solve the inverse problem Information theory and computer vision J.J. Gibson Texture gradient

  7. But it is insufficient to solve the problem uniquely!

  8. Heuristic assumptions Veridical perception vs. Perceptual illusions Helmholtz Probabilistic view of perception Leading to unique interpretation Solving the inverse problem

  9. Computational approaches to ecological optics Marr’s 2.5-D sketch David Marr X Modules

  10. Sources of depth information -Depth cues • Ocular information / Optical information • Binocular information / Monocular information • Static information / Dynamic information • Absolute information / Relative information • Quantitative information / Qualitative information

  11. Sources of depth information -Depth cues • Ocular information • Stereoscopic information • Dynamic information • Pictorial information

  12. Accommodation • Ocular/Monocular/Static/Absolute/Quantitative • Visual system should have access to the information about the tension of the muscles • Useful for close distances • Accommodation is derived by image blur so that the output of high spatial frequency channels is maximized • The best depth cue in the African chameleon

  13. Convergence • Ocular/Binocular/Static/Absolute/Quantitative • Useful for close distances • Convergence and accommodation are not independent

  14. Stereoscopic information Finger Experiment • Optical/Binocular/Static/Relative/Quantitative • Binocular disparity Direction of disparity: Crossed disparity: close Uncrossed disparity: far Magnitude of disparity: How much closer or farther Effective within 30 meters

  15. Stereoscopic informationThe Horopter Also fixation point has zero disparity.

  16. Stereoscopic information Diplopia (doubleness) Repeat finger experiment Stereoblindness in Strabismus, also in children with cataract in one eye Panum’s fusional area

  17. Stereograms Crossed convergence method Uncrossed convergence method Seeing stereograms with Stereoscope

  18. The correspondence problem

  19. Random Dot Stereograms Bela Julesz However, there may well be some primitive shape analysis before stereopsis.

  20. How to construct RDS?

  21. Computational Algorithms for solvingthe correspondence problem e.g. Marr-Poggio, 1977 taking heuristic constraints into account (e.g. surface opacity and surface continuity)

  22. Autostereograms Christopher Tyler

  23. Autostereograms

  24. Autostereograms

  25. Vertical Disparity

  26. Da Vinci Stereopsis

  27. Physiological mechanisms of binocular disparity • V1: Responds to zero or near-zero disparity • V2: Responds to large disparities (Hubel & Wiesel, Barlow & Blakemore) • Recently V3A, V4 and MT Recording from V2

  28. Disparity selectivity in area MT

  29. fMRI of Stereopsis

  30. Binocular Rivalry Red/Green filter glasses Convergence method Mirror devices

  31. Dynamic Information Old depth cues in evolution • Motion Parallax Objects closer to you travel at faster speeds and in the opposite direction; further objects travel slower and in the same direction.

  32. Dynamic Information • Optic flow (optic expansion)

  33. Dynamic Information • Kinetic depth effect (KDE) Rigidity heuristic

  34. Pictorial Information • Linear perspective

  35. Pictorial Information • Horizon

  36. Pictorial Information • Relative size • Familiar size: absolute depth cue

  37. Pictorial Information • Texture gradients systematic changes in the shape and size of texture elements Notice to the background of slides!

  38. Pictorial Information • Partial occlusion or interposition

  39. Junctions

  40. Pictorial Information • Shading

  41. Pictorial Information • Cast shadows Perceiving the height of objects

  42. Pictorial Information Non-homogeneous textures, 2004

  43. Integration/Interaction of different depth cues Pseudoscope Cue conflict between disparity and monocular depth cues

  44. Main Reference: Vision Science Palmer (Chap 5)

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