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THEORIES OF COLOUR VISION

Arnelit Philip Mani 2nd DC Economics 1719

Agenda• What is colour vision?• Perception of colour• Types of Colours• Types of Vision• History and theories• Conclusion

What is color vision ???

• Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies ) of the light they: reflect, emit, transmit .

Perception of colour Colour vision is a function of cones Better appreciated in phototopic conditions Scotopic vision- all colors seen as gray-Purkinje

shift Perception of colour depends upon

spectral composition of light coming from an object & emanating from surrounding State of light adaptation of subject

Contd…• For humans, the shortest light waves are

seen as violet and light waves that get longer and longer are seen as blue, then green, then yellow, then orange, and the longest are seen as red.

Types of ColoursPrimary colours

Complementary colours

 Types of Vision• Sensation of white

vision with no colour vision

Achromatic

• Spectral colour vision & Extra spectral colour vision - i.e., Mixing of two spectrum

Chromatic

HISTORY AND THEORIES• There are over one hundred theories that have been

advanced to explain color effects. Most of them may beclassified under three headings:

Specificity of cone function, assuming that one set of cones mediates onlyone particular color;

non-specificity of cone function,assuming that each cone is capable of mediating the wholegamut of color experience; and

those hypotheses whichhold that the determination of color is partly a function ofthe higher nerve centers.

Aristotle ( 4th century B.C)

• In Ancient Greece, Aristotle developed the first known theory of color. He postulated that God sent down color from the heavens as celestial rays. He identified four colors corresponding to the four elements: earth, fire, wind, and water.

Leonardo da Vinci• Leonardo da Vinci was the first

to suggest an alternative hierarchy of color. In his Treatise on Painting, he said that while philosophers viewed white as the "cause, or the receiver" of colors and black as the absence of color, both were essential to the painter, with white representing light, and black, darkness. He listed his six colors in the following order: white, yellow (earth), green (water), blue (air), red (fire), and black.

Sir Isaac Newton• The detailed understanding of the

science of color began in 1666, when Isaac Newton, using two prisms, observed that white light was composed of all the colors of the rainbow, and could be identified and ordered.

• Newton first used the word "spectrum" for the array of colors produced by a glass prism. He recognized that the colors comprising white light are "refracted" (bent) by different amounts.

• Newton assigned seven colors to the spectrum in an analogy to the musical scale.

George Palmer•  George Palmer proposed an essentially

correct explanation of colour vision – without public resonance.

• The retina must be composed of three kinds of fibers, each susceptible of being stimulated by only one of the three primary rays.

• Equal sensibility of these three classes of fibers constitutes true vision; any deficiency of sensibility of any class constitutes false vision.

Trichromatic or Young Helmholtz Maxwell Theory• postulates three different receptors maximally

sensitive to wavelength in different regions of visual spectrum.

• Three peaks are• 440 to 450 nm - blue spectrum• 535 to 550 nm - green spectrum• 570 to 590 nm - red spectrum

DrawbacksThough it accounts well for laws of

color mixing, has difficulty with other basic phenomena

• Dichromats who confuse red with green can see yellow

• Difficulty in explaining complementary color after-images

Herring’s Theory of Opponent processing

• Two chromatic (red-green and blue-yellow) and one achromatic (black and white) mechanism

• These pair sensation in an opposing or antagonistic manner

• Presence of one of the color of the pair excludes the other color perception and presence of both nullify each other

THEORY OF DOMINATOR-MODULATOR• Ragnar Arthur Granit•  In addition to the three kinds of

photosensitive cones—the colour receptors in the retina,some optic nerve fibres (dominators) are sensitive to the whole spectrum while others (modulators) respond to a narrow band of light wavelengths and are thus colour-specific.

• Granit also proved that light could inhibit as well as stimulate impulses along the optic nerve.

CONCLUSION• Every object seems to bear one or more

colors, making our world look brightly colored. Blue waters, green grass, and colourful clothes – these do not have color at all. 

• Psychologists say that color is an experience of the mind. All objects only reflect or produce light in different intensities, amplitudes and wavelengths.

• The process by which light information is processed through the sensory organs and the brain can be explained by the above discussed theories.