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A Concise History of the Chromaticity Diagram from Newton to the CIE Standard Colorimetric Observer A Concise History of the Chromaticity Diagram from Newton to the CIE Standard Colorimetric Observer Claudio Oleari Dipartimento di Fisica Università di Parma CREATE 2010, Gjøvik

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I am not an historian (but I like History) !

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warning All phenomena that follow hold true for colour matching in aperture mode. !

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SIMULTANEOUS CONTRAST or BRIGHTNESS INDUCTION SIMULTANEOUSCHROMATIC CONTRAST SIMULTANEOUS CHROMATIC CONTRAST

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aperture mode typical of the psycho-physical colorimetry

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The protagonists Galilei Newton Young (Göthe) Helmholtz Grassman Maxwell Hering Schrödinger The historical steps centre of gravity rule three kind of photoreceptors (fibres) ZERO ORDER tristimulus: colour measure in ZERO ORDER approximation The standards CIE 1931-CIE 1964-CIE 1976 FIRST ORDER The standards CIE 1931-CIE 1964-CIE 1976 OSA-UCS system ( ) “Colour Appearance”: towards the colour measure in FIRST ORDER approximation (Göthe against Newton) Helmholtz-Hering Controversy trichromacy Le Blom, Palmer

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Indeed, rays, properly expressed, are not coloured. (Isaac Newton)

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Any colour computation needs colour measurement. But Colour is a sensation. Then the question: Can colour be measured ?

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COLOUR IS SUBJECTIVE. This could induce us to deny a priori the colour measurement. On the contrary, colour can be measured because generally different persons agree in the judgment of the metameric colour matching, i.e. they affirm that different physical radiations appear equal. (The comparison of the colour sensations among different individual observers is not required and the measurement of colour sensations is transformed into the physical measurement of the luminous radiations, which induce equal colour sensations in the normal observers.) A correspondence between luminous radiations and colour sensations is realised, consequently the colour is indirectly measured by measuring the luminous radiation.

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? colour matching in bipartite field R+G+B?R+G+B? B G R ?

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Isaac Newton New theory about light and colour (1671) Opticks (1704) Franco Giudice Ed., Isaac Newton, Scritti sula luce e sul colore, BUR, 2006 EXPERIMENTUM CRUCIS (1671) No individual ray, no single refrangibility, is corresponding to white. White in a heterogeneous mixture of differently refrangible rays.

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ADDITIVE SYNTHESIS OF SPECTRAL LIGHTS 2 f

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CENTER OF GRAVITY RULE Light Orange colour

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CENTER OF GRAVITY RULE CENTER OF GRAVITY RULE

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R Y ry Barycentric Coordinates and mixing colour lights Barycentric Coordinates and mixing colour lights balance scales 2

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b r g (R,G,B)(R,G,B) B R G r g b Chromaticity Diagram r = R/(R+G+B) g = G/(R+G+B) b = B/(R+G+B) Barycentric Coordinates Barycentric Coordinates Barycentric Coordinates and mixing Barycentric Coordinates and mixing independent colour lights 3

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Three lights are independent if none of these lights is matched by a mixture of the other two lights.

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Barycentric Coordinates and mixing 4 independent (?) colour lights Can we use a three dimensional yoke in a four dimension space NO! Because four independent colours are not existing!! TRICHROMACY ?

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CENTER OF GRAVITY RULE CENTER OF GRAVITY RULE constraint among spectral lights METAMERISM

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TRICHROMATIC COLOR RIPRODUCTION & REAL PRIMARIES R B G An RGB system cannot reproduce all the real colours! Instrumental reference frame

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B G Negative light source!?!? C B + G R = C ????? B + G = R + C Phenomenon explained by Maxwell 180 years later R

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B G B + G R = C ????? B + G R + C = Q C METAMERISM R Q

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… it is such an orange as may be made by mixing an homogeneal orange with a white in the proportion of the line OZ to the line ZY,... I. Newton METAMERISM

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NOT mixed orange and white powders BUTlights reflected … it is such an orange as may be made by mixing an homogeneal orange with a white in the proportion of the line OZ to the line ZY, this proportion being NOT of the quantities of mixed orange and white powders, BUT the quantities of the lights reflected from them. I. Newton

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b( ) g( ) If r( ) + g( ) b( ) = C = unit spectral light B + G R + C = Q C COLOUR-MATCHING FUNCTIONS r( ) Q

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COMPLEMENTARY COLOURS ?!?!?

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COLORI COMPLEMENTARI COLORI COMPLEMENTARI ?!?!? COMPLEMENTARY COLOURS ?!?!?

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complementary spectral lights The existence of pairs of spectral lights that can be mixed to match white (complementary spectral lights) was not securely established until the middle of faint anonymous colour White presented an especial difficulty for Newton, who wrote: (1671) - “There is no one sort of rays which alone can exhibit this [i.e. white]. This is ever compounded, and to its composition are requisite all the aforesaid primary colours.” (1704) - “if only two of the primary colours which in the circle are opposite to one another be mixed in an equal proportion, the point Z shall fall upon the centre O and yet the colour compounded of these two shall not be perfectly white, but some faint anonymous colour. For I could never yet by mixing only two primary colours produce a perfect white. Whether it may be compounded of a mixture of three taken at equal distance in the conference.” yellow and blue Christian Huygens: (1673) – “two colours alone (yellow and blue) might be sufficient to yield white.”

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Newton’s mistake and open problems: 1) angular position of the spectral lights (Primary Colours) on the colour circle are in relation to the musical notes and not to the colour complementarity 2) all the Magenta hues are represented by a point in the colour circle 3) Circular shape is only an approximation

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four independent colours are not existing!! TRICHROMACY

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ADDITIVE MIXING OF COLOURED LIGHTS R B G R G B r g b

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Grundig television

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SUBTRACTIVE MIXING OF COLOURS in screen plate printing

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CYAN YELLOW MAGENTA BLUE GREEN RED BLACK WHITE Demichel (1924) – Neugebauer (1937) Additive mixing of 8 colour lights

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Demichel (1924) – Neugebauer (1937) Additive mixing of 8 colour lights

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TRICHROMACY of colour mixture: impalpable trichromacy ↔ ↔ material trichromacy - TRICHROMACY and development of three-colour reproduction - TRICHROMACY in opposition to Newton’s optics

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Material Trichromacy 1725 Jakob Christoffel Le Blon German printer Jakob Christoffel Le Blon ( ): Coloritto : or the Harmony of Coloring in Painting Reduced to Mechanical Practice ← printing ← additive and subtractive colour mixing ← Black & White

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redyellowblue black Le Blon innovated a system for using three separate printing plates, each inked with one of the painter's primary colors red, yellow and blue (and sometimes a fourth plate inked with black) to create full color mezzotint prints (the practical basis for today's multicolor process printing). second and final stages in Le Blon's four color printing method (c.1720)

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Jacques Fabian Gautier d'Agoty, Anatomie generale des viscères en situation, de grandeur et couleur naturelle, avec l'angeologie, et la nevrologie de chaque partie du corps humain, Gautier?, Paris (1752) Red-yellow-blue as primary material colours & black

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Towards the definition of imaginary primaries 1757 – Mikhail Vasil’evich Lomonosov 1777 – George Palmer 1780 – John Elliot MD 1802 – Thomas Young (1840 – David Brewster)

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REAL & IMAGINARY PRIMARIES Z Y X

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George Palmer (1777)

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Young’s contribution to understand Newton’s theory Light is a wave phenomenon Understanding of the light interference phenomenon Trichromacy related to three kinds of “fibres” in the retina, differently resonating if crossed by light Rotating disk for mixing colours (Claudius Ptolomaeus ≈100 – 175) Thomas Young (1802)(1817)

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Hermann Günther Graßmann (1853)

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Hermann Günther Graßmann(1853) Graßmann’s laws, as rewritten by Krantz (1975), state that the following linearity properties hold true for colour stimuli A, B, C and D, 1.- simmetry law if A B then B A 2.- transitivity law if A B and B C then A C 3.- proportionality law if A B then a B a A real a additivity law if A B and C D then ( A + C ) ( B + D ) The whole set of colour stimuli constitutes a linear vector space, named tristimulus space. tristimulus space. 1.- simmetry law if A B then B A 2.- transitivity law if A B and B C then A C 3.- proportionality law if A B then a B a A real a additivity law if A B and C D then (A + C) (B + D)

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Hermann von Helmholtz (1852) (1855) (1866)

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- complementary colours - magenta hues - chromaticity diagram

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REAL SPECTRAL PRIMARIES

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IMAGINARY PRIMARIES Colour-Matching Functions in fundamental reference frame

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R V A - fundamental reference frame - imaginary primaries

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Helmholtz considers the hypothesis of Young and Grassmann resonating fibres Young-Helmholtz Theory R V A

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James Clerk Maxwell (1857)

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Maxwell’s rotating rotor Rotating disk for mixing colours (Claudius Ptolomaeus ≈100 – 175)

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Dpt Exp.Psychology, Cambridge University Check of Newton’s centre of gravity rule R B G trilinear mixing triangle (c.1860)

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Red Green Blue Instrumental reference frame Red-Green-Blue real primaries Fundamental reference frame imaginary primaries

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(K = Katherine) Colour-matching functions in instrumental reference frame CIE 1931 observer

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Colour-Matching Functions: Maxwell’s minimum saturation Method R = nm (rosso) G = nm (verde) B = nm (blu) Colour matching of two beams

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Helmholtz-Hering controversy (1872)

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Ervin Schrödinger (1920)

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- fundamental reference frame, - “Helligkeit” equation and Alychne - tristimulus space metrics - Hering’s chromatic opponencies Ervin Schrödinger (1920)

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tristimulus space and fundamental reference frame Chromaticity diagram König’s Colour-matching functions or König’s fundamentals

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Lv=eRR+eGG+eBBLv=eRR+eGG+eBB Exner’s coefficients (R, G, B) (e R, e G, e B ) Schrödinger’s “Helligkeit” equation LUMINANCE

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towards the Colourimetric Standard Observer CIE 1931

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X Y Z alychne Standard Colourimetric Observer CIE 1931 (D. B. Judd introduced the Schroedinger’s alychne) )( x)()( Vy

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alychne From Newton to Schrdinger & Judd From Newton to Schrödinger & Judd

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q1q1 q2q2 q W1W1 W2W2 q1q1 q2q2 q Alychne CENTER OF GRAVITY RULE

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Newton 1671 (1704) CIE 1931 CENTER OF GRAVITY RULE

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Young’s hp (1802) 1) Young’s hp (1802): three kinds of independent photoreceptors exist, L, M and S, with proper spectral sensitivities. Rushton’s univariance hp (1972) 2) Rushton’s univariance hp (1972): the photochemical effect of a photon, once absorbed by the pigment of a photoreceptor, is independent of its energy; the difference among photons with different energy is the probability to be absorbed (This law is related to the Einstein photochemistry law : “one photon is absorbed in any photochemical event”). Macula lutea and lens filtering 3) Macula lutea and lens filtering correspondence 4) in any defined visual situation, colour sensations are in one to one correspondence with the number of photon absorbed (i.e. with the powers (L, M, S) absorbed by the three kinds of photoreceptors). Hypotheses for “first zone” colour specification Today

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Thank you for your kind attention Claudio Oleari

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R W +G W +B W R +G +B +M R W+ G W + B W R M monochromatic stimulus G B Maxwell’s minimum saturation method

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W M + R +B R B G W W M + G + B W M + R + G 0 WWW BGRBGRM 0 ˆ ˆ ˆˆ ˆ ˆ )( ˆ )( ˆ )( ˆ BGRBGRBGR WWW BGRBGRbgrM 0)( ˆ )( ˆ )( ˆ WWW BBMbGGMgRRMr BGR M BB b M GG g M RR r WWW )(,)(,)(

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? Maximum saturation Method Maximum saturation Method in bipartite field G +B R +L e( ) B G L e( ) R

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(K = Katherine) Colour-matching functions in instrumental reference frame CIE 1931 observer

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König’s Colour-matching functions or König’s fundamentals Chromaticity diagram tristimulus space and fundamental reference frame

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