1. Copyright Catherine M. Burns1 VISION

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 Brightness = an intensity measurement

3. Copyright Catherine M. Burns3 Screen Colour vs. Paint/Pigment Screen colour is additive (adds light) Pigment is subtractive (reflects light so decreases light) Screens RGB Pigment CYM

4. Copyright Catherine M. Burns4 Colour Maps The CIE space - How to make colours with Red/Green/Blue

5. Copyright Catherine M. Burns5 The RGB Colour Cube

6. Copyright Catherine M. Burns6 Measurement of Intensity Depends on where the source is Luminous Flux: intensity of energy from a source Unit: candela or lumins luminous flux

7. Copyright Catherine M. Burns7 Measurement of Intensity Illumination or illuminance: Amount of energy that lands on a surface Units: foot candle or lux luminous flux illumination

8. Copyright Catherine M. Burns8 Measurement of Intensity Luminance: Amount of light reflected back from a surface Unit: Candela/m 2 or foot-lamberts (FL) luminous flux illumination luminance

9. Copyright Catherine M. Burns9 Reflectance A measure of how much a surface reflects Ratio of luminance and illuminance Reflectance (%) luminance (FL) illuminance (FC)

10. Copyright Catherine M. Burns10 The Eye www.eyenet.org/public/anatomy/anatomy.html

11. Copyright Catherine M. Burns11 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"

12. Copyright Catherine M. Burns12 Retina –flat surface of receptor cells –130 million rods and 7 million cones –cones provide colour vision during daylight –rods are more sensitive but don't provide colour for dim light, night vision –photochemical reactions to produce nerve impulses

13. Copyright Catherine M. Burns13 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!

14. Copyright Catherine M. Burns14 Visual Angle

15. Copyright Catherine M. Burns15 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

16. Copyright Catherine M. Burns16 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"

17. Copyright Catherine M. Burns17 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

18. Copyright Catherine M. Burns18 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

19. Copyright Catherine M. Burns19 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!

20. Copyright Catherine M. Burns20 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

21. Copyright Catherine M. Burns21 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

22. Copyright Catherine M. Burns22 Glare excessive brightness which wipes out visual detail

23. Copyright Catherine M. Burns23 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

24. Copyright Catherine M. Burns24 Ergonomics for VDTs 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

25. Copyright Catherine M. Burns25 Visual Illusions The Ponzo Illusion: Both lines are the same length

26. Copyright Catherine M. Burns26 Visual Illusions Muller-Lyer Illusion: Both horizontal lines are the same length

27. Copyright Catherine M. Burns27 Visual Illusions Both rectangles are the same size

28. Copyright Catherine M. Burns28 Visual Illusions Center shape is a square