1. Copyright Catherine M. Burns 1 VISION Text Chapter 4 p. 61-89

2. Copyright Catherine M. Burns2 The Visual System  sensor system for electro-magnetic radiation  typically 400nm (blue-violet) to 700nm (red)  Hue = colour (mix of red, green, blue)  Saturation = purity of wavelength in terms of red, green, blue Pure red=Saturated  Brightness = an intensity measurement

3. Copyright Catherine M. Burns3 Visual Spectrum UltravioletVioletBlueGreenYellowRedInfra-red 700nm400nm Text Figure 4.1a

4. Copyright Catherine M. Burns4 Screen Colour vs. Paint/Pigment  Screen colour is additive (adds light)  Pigment is subtractive (reflects light so decreases light)  Screens RGB  Pigment CYM

5. Copyright Catherine M. Burns5 Colour Maps The CIE space - How to make colours with Red/Green/Blue light Screen colour palettes Text Figure 4.1b

6. Copyright Catherine M. Burns6 The RGB Colour Cube Adds saturation (white- black axis)

7. Copyright Catherine M. Burns7 Measurement of Intensity  Depends on where the source is  Luminous Intensity or Luminous Flux: Actual light energy of a source  Unit: candela luminous flux

8. Copyright Catherine M. Burns8 Measurement of Intensity  Illumination or illuminance: Amount of energy that lands on a surface  Declines with the square of the distance from the source  Units: foot candle or lux luminous flux illumination

9. Copyright Catherine M. Burns9 Measurement of Intensity  Luminance: Amount of light reflected back from a surface  Unit: Candela/m 2 or foot-lamberts (FL) luminous flux illumination luminance

10. Copyright Catherine M. Burns10 Reflectance  A measure of how much a surface reflects  Ratio of luminance and illuminance Reflectance (%) luminance (FL) illuminance (FC) White very reflective vs. black

11. Copyright Catherine M. Burns11 The Eye www.eyenet.org/public/anatomy/anatomy.html

12. Copyright Catherine M. Burns12 Elements of the Visual System  Cornea - performs 1/3 of total refraction  Pupil - controllable, an aperture which controls the amount of light energy entering  Lens - complex refraction (gradient refraction optics) shape is controllable, "flexes", accommodation to near and far doesn't stop growing loses flexibility around your 40s. "reading glasses"

13. Copyright Catherine M. Burns13  Retina flat surface of receptor cells 130 million rods and 7 million cones cones provide colour vision during daylight rods are more sensitive (light level activation) but don't provide colour for dim light, night vision photochemical reactions to produce nerve impulses

14. Copyright Catherine M. Burns14  fovea entirely cones, on the optic axis of the eye most dense region move eyes to look at things sharpest vision each foveal cone has its own nerve fibre other areas of the retina don't - think data transfer, data bus!

15. Copyright Catherine M. Burns15 Visual Angle Height H Distance D VA=arctan(H/D)

16. Copyright Catherine M. Burns16 The Visual Field  sharp vision along 1 degree v.a. (fovea)  middle field: mix of rods and cones, up to 40 degree angle  periphery: primarily rods

17. Copyright Catherine M. Burns17 Sensory Processing Limitations  Contrast sensitivity Uses luminance levels of two areas “L” light and “D” dark Ratio of the difference over the sum C=(L-D)/(L+D) People each have a minimum contrast level they can detect

18. Copyright Catherine M. Burns18 Contrast Sensitivity Measures

19. Copyright Catherine M. Burns19 Color “Blindness”  7% of male population is color deficient  Most common is red-green  Design advice Design for monochrome first and add color later for emphasis

20. Copyright Catherine M. Burns20 Accommodation  lens continually readjusts to keep objects at different distances in focus. autofocus natural "resting" accommodation is about 1m close work can cause it to be difficult for the lens to readjust afterwards to longer distances "temporary myopia"

21. Copyright Catherine M. Burns21 The Near Point  near point - closest distance you can focus on.  indicates lens flexibility  moves out with age  moves farther out with fatigue -> visual fatigue

22. Copyright Catherine M. Burns22 Presbyopia  lens loses its ability to flex  close work becomes difficult  need for reading glasses  everyone goes through it starting at 40  accommodating requires muscular work and can create fatigue

23. Copyright Catherine M. Burns23 Pupil changes  a control system - more light, smaller diameter, etc.  takes a measurable length of time to adjust  rapid light changes can cause retinal damage because pupil doesn't adjust quickly enough  physical discomfort!

24. Copyright Catherine M. Burns24 Pupil Size  Regulated by: brightness of the visual field focus distance (contracts for near) emotional states - dilates with alarm, happiness, mental work contracts with fatigue and sleepiness

25. Copyright Catherine M. Burns25 Retinal Adaptation  retina is also a control system darkness rods come out, bright light cones come out see more in a dark room 10 to 15 minutes later complete dark adaptation takes 45 minutes adaptation dark to light much more quickly, a minute or two dark workplaces typically use red light to maintain adaptation

26. Copyright Catherine M. Burns26 Glare  excessive brightness which wipes out visual detail

27. Copyright Catherine M. Burns27 Visual Fatigue  irritation, burning, tearing watering of eyes, red eyes  double vision  headaches  reduced acuity and accommodation  Work Impact: mistakes, loss of productivity, lower quality work, complaints, higher accident rate

28. Copyright Catherine M. Burns28 Ergonomics for Computer Screens  refresh rate high enough to remove flicker  use larger characters for wider population, older people  remove sources of reflection on screen  don't have bright lights directed into screen, washes out screen  dark room versus light room a personal preference or depends on need to switch work

29. Copyright Catherine M. Burns29 Visual Illusions The Ponzo Illusion: Both lines are the same length

30. Copyright Catherine M. Burns30 Visual Illusions Muller-Lyer Illusion: Both horizontal lines are the same length

31. Copyright Catherine M. Burns31 Visual Illusions Both rectangles are the same size

32. Copyright Catherine M. Burns32 Visual Illusions Center shape is a square

33. Copyright Catherine M. Burns33

34. Copyright Catherine M. Burns34 Shade context illusions Shockwave files Gray blocks 1 Gray blocks 2 Whites Gray blocks 3

35. Copyright Catherine M. Burns35 Center surround effects  Haze Haze  Vasarely Vasarely