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		       CS 99D - Color #2 - March 6, 2001

				  Marc Levoy
			      Stanford University
				   (c) 2001

		      (with corrections, March 14, 2003)

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		    *** Modern tristimulus color theory ***

1773-29	Thomas Young (from Park and web)
	o physician in London, amateur physicist, member of Royal Society
	o classic double-slit experiment demonstrating interference
	o argued, paying "infinite respect" to Newton, that the latter's work,
	  which had frozen further research on the nature of light,
	  in fact did not preclude wave theory
	o began decoding the Rosetta Stone (Hierglyphs, Demotic, Greek),
	  decoding completed by Jean Champillion in 1822
	o proposed three receptor systems, three primaries

(from 1995 CS 248 course notes)
	o monochromats
	o dichromats, trichromats
	o the tristimulus sensitivity functions (rho,gamma,beta curves)
	o superposition + scaling = linearity
	o the color matching experiment
	o the tristimulus matching functions (R,G,B curves for given primaries)
	o the locus of spectral colors (rho,gamma,beta space)
	o spectral locus as parametrically defined curve
	o gamut of reproducible colors
	o gamut of perceivable colors

Why are 3 overlapping receptor systems better than 2?
	o 3 gives a volume of perceivable color; 2 gives a planar figure
	o Color blind people have a 2-receptor system
	o Many mixtures of pure spectal colors that are metamers in a
	  2-receptor system can be distinguished in a 3-receptor system
	o Sunglasses with one filtered eye give a 6-receptor system,
	  hence hexachromatic vision
	
(1995 CS 248 course notes, continued)
	o rho,gamma,beta-space versus RGB-space, revisited
	o the rgb chromaticity diagram
		-> xyz chromaticity diagram, FVDFH, pl. II-2, after p. 617

Opponent color theory:
	o evidence 1: we don't see red-greenish colors or blue-yellowish colors
	o evidence 2: we can measure an L-M signal after the LGN in the pathway
	o usefulness: decorrelation -> maximum use of available bandwidth
	o relation to YIQ and NTSC
		-> Wandell's Foundations of Vision, p. 304+, color plate 7

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