Graphics and Human Perception

1. Graphics and Human Perception Presented by: Tumkur Vani, Kanti Graphics and Human Perception

2. What is Perception? • Extraction of information from sensory stimulation.  • An active, selective process, influenced by a person's attitude and prior experience.  Graphics and Human Perception

3. Why is Perception important in Graphics? Graphics and Human Perception

4. Large variety of advanced electronic imaging equipment Limiting factor : Need to understand and reactto information displayed and collected by Human Perceptual System Graphics and Human Perception

5. Psychophysics Study of human reactions to physical stimuli or input (EXTERNAL) Does not explain how or why we react Graphics and Human Perception

6. Design of Imaging devices:Must be closely coupled to human perceptual systemBetter impedance-match between opto-electronics and our neurons Graphics and Human Perception

7. In Entertainment industry:“How little information do you need to make the picture look good?” Graphics and Human Perception

8. In critical technical analysis using graphics: “How much information can we capture and transmit to give the viewer what he or she would see if present at the scene?” Graphics and Human Perception

9. Weird stuff HVS maintains color constancy despite ambient shifts Extreme sensitivity to spectral (color) differences No such thing as “static image”! - Saccadic motion of eyeball Graphics and Human Perception

10. If color can’t be recognized in the first few frames, object will be WIPED from visual memoryCritical in situations like: - Cancer cell detection - Camouflaged tank detection - Subtle motion of an object on a distant planet Graphics and Human Perception

11. Perceiving Our world Graphics and Human Perception

12. SHADOW CUES Graphics and Human Perception

13. LINES AND CURVES Graphics and Human Perception

14. DOUBLE IMAGES Graphics and Human Perception

15. IMPOSSIBLE FIGURES Graphics and Human Perception

16. The Brain can be Tricked!!! Graphics and Human Perception

17. Why is Perception important in Graphics? Physical accuracy in rendering does not guarantee that the displayed images will have a realistic visual appearance. Realism Physically correct, perceptually equivalent to the scene Graphics and Human Perception

18. How does the eye work? Graphics and Human Perception

19. Pupil • Lens • Retina: • Protective layer • Rods and Cones • Bipolar cells • Ganglion layer • Optic Nerve • Light -> electrical nerve impulses Graphics and Human Perception

20. Graphics and Human Perception

21. Spatial awareness- Stereoscopic vision Graphics and Human Perception

22. Paradigm shifts Compression algorithms assume that motion vectors are the most important factor in an imaging system. IN REALITY: Brain senses the object in the foll sequence: COLOR, EDGE, MOTION - If WRONG sequence, then brain does not sense the object at all! HVS concentrates on selected areas due to: - SUBLIMINAL cues, - NOT conscious visual cues HVS processes sensory input using mechanisms OUTSIDE visual cortex Graphics and Human Perception

23. Unexpected and counter-intuitive data Important revisions to long-held theories on : Contrast detection Temporal and spatial color perception Motion sensitivity Object and pattern detection Visual illusions Sequencing of subliminal and conscious events Graphics and Human Perception

24. Design Questions How should color be used? What graphical entities can be accurately measured? How many distinct entities can be used without confusion? What primitives do human detect pre-attentively? What level of accuracy do we perceive various primitives? How do we combine primitives to recognize complex phenomena? Graphics and Human Perception

25. Perception-driven rendering algorithms:Ward's contrast-threshold tone reproduction operatorDouglass-Peucker line simplification algorithmPerceptually Based Adaptive Sampling Algorithm - Bolin, M. and G. Meyer Perceptually driven shape simplification algorithm Graphics and Human Perception

26. Visual function changes dramatically over the range of Environmental Illumination. Graphics and Human Perception

27. Producing Realistic Images Model : • Physical behavior of light propagation • Perceptual response parameters Graphics and Human Perception

28. Tone Reproduction Operators Overcome the limits of conventional CRT displays Determine how to best display simulated environments within the limited dynamic range available. Graphics and Human Perception

29. Tone Reproduction Operators Preserve the apparent brightness of scene features Preserve apparent contrast and visibility Psychophysical model of glare: Implements a glare filter that increases the apparent dynamic range of images. Graphics and Human Perception

30. Model of adaptation Includes the effects of adaptation on threshold visibility, color appearance, visual acuity, and changes in visual sensitivity over time. Graphics and Human Perception

31. Visual function across Range of Light Graphics and Human Perception

32. Applications Efficient software ( by not computing those parts of a scene which the human will fail to notice) Predicting visibility (eg from Cockpit) Architectural design Special effects or advertising Virtual sets in a show Reconstruction of historic buildings or places for educational purposes Graphics and Human Perception

33. Conclusion Great deal of potential Images: Perceptually accurate, Physically correct, Faithful represenrations Allows for high level of confidence in computer-imagery Graphics and Human Perception

34. References AS IF YOU WERE THERE : Matching Machine Vision to Human Vision - Richard Jay Solomon (Univ. of Pennsylvania) Program on Vision Science & Advanced Networking (2002) www.hybridvigor.net/human/pubs/index.htm Perceptually Adaptive Graphics Ann McNamara and Carol O'Sullivan - ACM SIGGRAPH AND EUROGRAPHICS CAMPFIRE http://isg.cs.tcd.ie/campfire (May 26th - 29th, 2001 Snowbird, Utah) http://library.thinkquest.org/C001464/cgi-bin/view.cgi?show_item=perception Visual Perception in Realistic Image Synthesis ( State of the art (STAR) Report) - Ann McNamara Eurographics 2000, Interlaken, Switzerland, August 2000 Graphics and Human Perception

35. Thank You Graphics and Human Perception