Depth Perception, with Emphasis on Stereoscopic Vision

1. Depth Perception, with Emphasis on Stereoscopic Vision Randolph Blake Visual System, Spring Semester March 24, 2003 Chapter 10 in McIlwain and Chapter 11 in Tovee http://www.psy.vanderbilt.edu/faculty/blake/StereoStuff/Stereopsis.htm

2. Specifying 3D shape and depth relations • motion

3. Specifying 3D shape and depth relations • motion

4. Specifying 3D shape and depth relations • motion

5. Specifying 3D shape and depth relations • motion • size

6. Specifying 3D shape and depth relations • motion • size • perspective

7. Specifying 3D shape and depth relations • motion • size • perspective

8. Specifying 3D shape and depth relations • motion • size • perspective

9. Specifying 3D shape and depth relations • motion • size • perspective • texture perspective

10. Specifying 3D shape and depth relations • motion • size • perspective • texture perspective • occlusion

11. Specifying 3D shape and depth relations • motion • size • perspective • texture perspective • occlusion • shading

12. Specifying 3D shape and depth relations • motion • size • perspective • texture perspective • occlusion • shading

13. Specifying 3D shape and depth relations • motion • size • perspective • texture perspective • occlusion • shading

15. Sir Charles Wheatstone’s Famous Invention

16. Stereograms (anaglyphs)

17. Stereograms (“Magic Eye”)

18. Stereopsis (literally, “seeing solid”)- 3D vision resulting from slight differences in left and right eye images, arising because the two eyes view the world from slightly different perspectives Disparity - slight differences in positions of “features” in left and right eye views • crossed disparity • uncrossed disparity • zero disparity

19. Magnitude of Disparity Signifies Depth Difference

20. Disparity Magnitude Also Varies with Viewing Distance stereopsis works only within 10 - 20 ft of the observer; once the visual axes are parallel, objects beyond the point of fixation provide no disparity

21. Magnitude of Disparity Depends on “IPD” “ipd” = interpupillary distance (averages 6.5 cm in humans)

22. Random-dot Stereograms (Julesz, 1971)

23. How They’re Made

24. How They’re Made

25. How They’re Made

28. How Does the Brain “Solve” This Problem?

29. What “features” does the brain match for stereopsis? original images “low” spatial frequencies “high” spatial frequencies”

30. What Happens When Binocular Matches Cannot Be Found? left eye right eye

31. Binocular Rivalry

32. Neural Bases of Disparity Registration

33. Neural Bases of Disparity Registration

34. Neural Bases of Disparity Registration zero disparity

35. Neural Bases of Disparity Registration uncrossed disparity

36. Neural Bases of Disparity Registration uncrossed disparity

37. Neural Bases of Disparity Registration

38. Neural Bases of Disparity Registration “crossed disparity

39. Neural Bases of Disparity Registration “crossed disparity

40. Neurons in visual cortex can match features between the two eyes and can “compute” retinal disparity. Is the problem of stereopsis solved? NO! Disparity must be scaled for distance. (Recall that a given disparity can be associated with different depth intervals, depending on viewing distance and on IPD.) Non-stereoscopic cues required for this “depth scaling”

41. http://www.3d-web.com/index.html http://www.stereographics.com/ http://www.psy.vanderbilt.edu/faculty/blake/StereoStuff/Stereopsis.htm