Vision: Subjective and Objective Issues

1. Vision: Subjective and Objective Issues Oleh Tretiak Medical Imaging Systems 2002

2. Why Study Vision • Understand how to display images • Understand what is seen • Understand how vision works

3. Sources of Information • Physics of vision • Neurophysiology of vision • Psychology of vision • Psychophysics

4. References • David Hubel, Eye, Brain, and Vision, Henry Hold & Company, 1995 • James P. C. Southall, Physiological Optics, Dover, 1961 • Vicki Bruce, Patrick R. Green, Mark A. Georgeson, Visual Perception: Physiology, Psychology, and Ecology, Psychology Press, 1996

6. Visual Pathway - Anatomy

7. Visual Pathway - Symbolic

8. The Retina and the Eye

9. The Eyeball

10. Vision and Eye Fixation (motion)

11. Half-retina maps

12. Layers of the Geniculate Nucleus

13. Section through Striate Cortex

14. Map From Retina to Striate Cortex

15. Striate Cortex Input/Output

17. The model is due to Gullstrand (1924). The power of the eye in this model ranges from 58.64 dptr (diopters) to 70.57 dptr. Most of the refraction (43 dptr) is due to the cornea.

18. Subjective Intensity (Contrast) Models • In a model for subjective intensity, let x by the brightness (power/area) and y the subjective brightness (contrast). Both x and y range from 0 to 100. • Logarithmic model: • Power law model: • On the next slide we show thirty four steps designed to produce uniform contrast with (1) linear, power law with gamma = 1, (2) power law, gamma = 0.7, and (3) logarithmic. Note that the appearance of this depends on the transfer function of the display.

20. Simultaneous Contrast Examples Background = 245, circles = 210, 225, and 235 Background = 70, circle = 60

21. The circles have the same objective intensity.

23. ‘Typical’ Visual Spatial Response

28. Mach Bands Subjective (perceived) value Objective value (intensity)

29. ‘Typical’ visual temporal response

30. Boundaries Texture Brightness

31. Shape Perception

32. Size Perception