2. O VERVIEW What is the colour The eye The sensation of the colour Colour vision effects Colour deficiencies Closure

3. C OLOUR W HAT I S T HE C OLOUR ? X-rays U-V rays Visible spectrum Infra red Radar Radio Cosmic rays 10 -8 10 -14 10 -12 10 -6 1 10 -4 (m) 10 +2 The light result of the feeling produced by the electromagnetic waves in a spectral field going from 380nm to 730nm. The light result of the feeling produced by the electromagnetic waves in a spectral field going from 380nm to 730nm. This area is called: visible spectrum This area is called: visible spectrum Each wavelength corresponding has a perceptive feeling called “colour”. We translate the colour as: red, yellow, green, cyan, blue, magenta Each wavelength corresponding has a perceptive feeling called “colour”. We translate the colour as: red, yellow, green, cyan, blue, magenta

4. C OLOUR W HAT I S T HE C OLOUR ? The daylight is white. Is it? 730 nm 380 nm  Newton: is the additive of all the colours of spectrum  Colour is the sensation that the eye receive from the quality and quantity of electromagnetic waves  Basic characteristics of colour:  Hue, saturation, brightness

5. C OLOUR H OW WE P ERCEIVE T HE C OLOUR THE EYE Is a remarkable biological invention, a shining triumph of the process of evolution. Although it was the detector that started us on mankind's exploration of the Cosmos, it has some shortcomings that ultimately limit that exploration: It has limited size and therefore limited light-gathering power. It has limited frequency response, since it can only see electromagnetic radiation in the visible wavelengths. It distinguishes a new image multiple times a second, so it cannot be used to accumulate light over a long period in order to intensify a faint image. It cannot store an image for future reference like a photographic plate can though the brain can.

6. T HE E YE 1.Cornea 2.Anterior chamber 3.Iris 4.Sclera 5.Choroid 6.Retina 7.Aqueous humour 8.Pupil 9.Crystalline lens 10.Posterior chamber 11.Fovea 12.Optical nerve

7. T HE E YE Diagram of organization of the retina Rods Cones Pigment epithelium Outer limiting membrane Muller cells Horizontal cells Dipolar cells Amacrine cells Ganglion cells Nerve fiber layer Inner limiting membrane The retina Photoreceptors that are sensitive to light When light is absorbed by the photoreceptors, the light energy is converted into electrical and chemical signals which sent from the to brain through ganglion cells and optic nerves. There are two kinds of photoreceptors:  rods  cones

8. T HE E YE Rods & Cones The rods  Are most sensitive to light and dark changes, shape and movement and contain only one type of light- sensitive pigment (scotopic conditions)  Are not good for colour vision.  The images generated by rod stimulation alone are relatively unsharped and confined to shades of grey  Are more numerous than cones in the periphery of the retina  The light sensitivity of rods is about 1000 times more than cone cells  There are about 120 million rods in the human retina

9. T HE E YE Rods & Cones The cones  Are not as sensitive to light as the rods  Are most sensitive to one of three different colours (green, red or blue) and usually referred to as photopic vision  Stimulation of these visual receptors results in what is know as true colour vision  There are about 6 million cones in the human retina  Signals from them are sent to the brain which then translates these messages into the perception of colour  They work only in bright light  Three types: S, L & M

10. T HE E YE Types of cones Each type is differentially sensitive to a different region of the visible spectrum  S: short-wavelength sensitive, most receptive at 419nm (blue), cyanolabe  M: middle-wavelength sensitive, most receptive at 531nm (green), chlorolabe  L: long-wavelength sensitive, most receptive at 558nm (red), erythrolabe

11. T HE E YE  Is the region of the retina that provides for the most clear vision.  There are NO rods...only cones.  The cones are also packed closer together here than in the rest of the retina.  Very few s-cones in fovea  Blood vessels and nerve fibers go around the fovea so light has a direct path to the photoreceptors. The fovea

12. T HE E YE Blind spot Approximately 14 o from the fovea No rods or cones Insensitive to light Hence NO vision  No problem: - binocular vision - continuous movement in high speed

13. F ROM THE E YE TO THE B RAIN The light which is absorbed by the photoreceptors is converted into electrical and chemical signals and through the ganglions is transmitted to the neurons in our eye and brain process All the nerve impulses generated in the retina travel back to the blind spot Axons in the optic nerve connect the blind spot with the optical centre Optical centre Retina Optic nerve

14. C OLOUR S ENSATION O F T HE C OLOUR Three main theories describe the colour vision: Trichromatic theory Hering opponent theory Modern opponent colour theory

15. C OLOUR S ENSATION O F T HE C OLOUR Trichromatic Theory  three receptor types with different spectral sensitivities  specific colour coded by pattern of responding across receptors (distributed coding)  The ratios of the signals are used to define the colour sensation Colour sensation Light Cones

16. C OLOUR S ENSATION O F T HE C OLOUR Hering opponent theory Based on observation of colour vision  Red, green, blue, yellow No colours could be described as a combination  -red+green  -blue+yellow Opponent colours

17. C OLOUR S ENSATION O F T HE C OLOUR Hering opponent theory adaptation responsible for afterimages

18. C OLOUR S ENSATION O F T HE C OLOUR Hering opponent theory The colour receptors had a red/green, blue/yellow and dark/light response Colour sensation Colour receptors Light

19. C OLOUR S ENSATION O F T HE C OLOUR Modern opponent colour theory Colour sensation SML Light Cones Cells Three receptor types with different spectral sensitivities detect the light Produce three processed signals that are then used to determine the colour sensation It is supported by psychological experiments

20. C OLOUR C OLOUR V ISION E FFECTS These effects and need to be taken into account when trying to model the colour vision system: CIELAB, RLAB, CIECAM97s There are more than 10 different vision effects that can be compensated for They take into account functions from the field of view, colour constancy through to the viewing conditions The most common are dark and light adaptation, and simultaneous contrast.

21. C OLOUR C OLOUR V ISION E FFECTS Dark and light adaptation Dark adaptation Occurs when the illumination decreases Example: walk into a darker room Light adaptation Occurs when the illumination increases Example: walk into a dark room into daylight

22. C OLOUR C OLOUR V ISION E FFECTS Simultaneous contrast Is the impact of the surround on the colour seen, which can make the same colour appear different

23. C OLOUR D EFICIENCIES Is the loss of colour discrimination Causes: Genetic photoreceptor disorders  Usually in males because the genes for the red and green colour receptors are located on the X chromosome, of which men have only one and women have two (red + green) Damage to the retina Damage to the optic nerve Higher brain areas implicated in colour processing include the parvocellular pathway of the lateral geniculate nucleus

24. C OLOUR D EFICIENCIES Types of colour defective vision: Dichromism: Protanopia Deuteranopia Tritanopia Anomalous trichromatism: Protanomaly Deuteranomaly Monochromatism: Rod monochromatism Cone monochromatism

25. C OLOUR D EFICIENCIES TYPEFORMCAUSE Red-green defects Protanomalytrichromaticdysfunctional L cones Protanopiadichromaticmissing L cones Deuteranomalytrichromaticdysfunctional M cones deuteranopiadichromaticmissing M cones Blue-yellow defects tritonopiadichromaticmissing S cones COLOUR VISION DEFECTS

26. C OLOUR D EFICIENCIES Protanopia the brightness of red, orange, and yellow is much reduced when compared to normal reds may be confused with black or dark grey protanopes may learn to distinguish reds from yellows and from greens "primarily” on the basis of their apparent brightness or lightness not on any perceptible hue difference Likewise, violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed that they become to be invisible.

27. C OLOUR D EFICIENCIES Deuteranopia the brightness of red, orange, and yellow and green is much reduced when compared to normal not on any perceptible hue difference aside from being different names that every one else around him seems to be in concurrence upon violet, lavender, purple, and blue all appear to be the same to a viewer with deuteranopia but without the dimming

28. C OLOUR D EFICIENCIES Tritanopia see the world in shades of reds and a type of green/turquoise colour but this varies individuals with blue-yellow defects confuse colours from yellow through green to blue tritanopes usually do not have as much difficulty in performing everyday tasks as do individuals with either of the red-green variants of dichromacy Because blue wavelengths occur at one end of the spectrum, and there is little overlap in sensitivity with the other two cone types, total loss of sensitivity across the spectrum can be quite severe with this condition

29. C OLOUR D EFICIENCIES Normal Protanopia Deuteranopia Tritanopia

30. C OLOUR D EFICIENCIES NORMAL PROTANOPIA DEUTERANOPIA TRITANOPIA

31. C OLOUR D EFICIENCIES ANOMALOUS TRICHROMATISM need 3 wavelengths to match all colours in spectrum, just like normal trichromats but they mix colour in different proportions than normal trichromats do protoanomaly – deficiency in L cone pigments (reduced sensitivity to reddish light) and the colours looks dim deuteranomaly – deficiency in S cone pigments (reduced sensitivity to greenish light) but the brightness of the colour is not effected can determine this condition using anomaloscope

32. C OLOUR D EFICIENCIES Monochromacy Complete inability to distinguish any colours is called monochromacy. It occurs in two forms:  rod monochromacy or achromatopsia  cone monochromacy

33. C OLOUR D EFICIENCIES Rod monochromatism or achromatopsia Where the retina contains no cone cells, so that in addition to the absence of colour discrimination, vision in lights of normal intensity is difficult Know as scotopic vision Do not provide a sharp image cause:  Adjacent rods are connected by gap junctions and so share their changes in membrane potential  Several nearby rods often share a single circuit to one ganglion cell  A single rod can send signals to several different ganglion cells It is cause of a disease called retinitis pigmentosa

34. C OLOUR D EFICIENCIES Cone monochromatism Where only a single system appears to be functioning, so that no colours can be distinguished, but vision is otherwise more or less normal When all three types of cone cells are stimulated equally then light is perceived as being achromatic or white

35. C OLOUR D EFICIENCIES NORMAL MONOCHROMACY

36. C OLOUR D EFICIENCIES Colour defective vision can be addressed with colour vision tests Ishihara colour vision tests Ishihara plates consist of a series of dots the colours of which are arranged so as to represent different numbers

37. C LOSURE The human eye is very complicated and sensitive. It is the only way to see the colours and understand the world. Although the eye has millions of rods and cones, theories are explaining how the colour vision works and scientists are trying to solve the colour defective vision, some people will never see all the colours, will never understand what the rest of us can see.

38. S UMMARY Understanding of vision Know how the eye works Appreciation of colour defective vision

39. R EFERENCES In process colour monitoring (module notes): Dr Mark Bohan Colour Theory (module notes): Dr Kuriakos Stathakis –A.T.E.I. of Athens MIT Encyclopaedia of the Cognitive Sciences Robert Wilson / Frank Keil, 1999 http://webvision.med.utah.edu/sretina.html#overview http//www.e-paranoids.com/c/co/color_blindness.htmlwww.e-paranoids.com/c/co/color_blindness.html http//:home.wanadoo.nl/paulschils/05.03.html http://www.accessexcellence.org/AE/AEC/CC/vision_background.html http://faculty.washington.edu/chudler/bigeye.html http://csep10.phys.utk.edu/astr162/lect/light/limitations.html http://www.yu.edu/faculty/rettinge/_private/perception/color.pdf http://www.tedmontgomery.com/the_eye/ http://en.wikipedia.org/wiki/Color_blindness http://www.webaim.org/techniques/visual/colorblind#deuteranopia http://micro.magnet.fsu.edu/optics/lightandcolor/vision.html http://www.psych.umn.edu/courses/HoldenJ/psy3031/psy3031day12.ppt#277,16,3 Kinds of Cones, 3 Pigments http://www.achromat.org/what_is_achromatopsia.html

40. Thank you for listening Any questions?