A Concise History of the Chromaticity Diagram from Newton to the CIE Standard Colorimetric Observer

1. A Concise History of the Chromaticity Diagramfrom Newton to the CIE Standard Colorimetric Observer Claudio OleariDipartimento di FisicaUniversità di Parmaclaudio.oleari@fis.unipr.it CREATE 2010, Gjøvik

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

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

4. The historical steps centre of gravity rule three kind of photoreceptors (fibres) tristimulus: colour measure inZERO ORDERapproximation The standards CIE 1931-CIE 1964-CIE 1976OSA-UCS system (1947-1974)“Colour Appearance”: towards the colour measure inFIRST ORDERapproximation The protagonists 1623 - Galilei 1704 - Newton 1802 - Young 1808 - (Göthe) 1852 - Helmholtz 1853 - Grassman 1857 - Maxwell 1872 - Hering 1920 - Schrödinger1931 ... trichromacy (Göthe against Newton) Helmholtz-Hering Controversy Le Blom, Palmer

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

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

7. 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.

8. colour matchingin bipartite field B G R ? R+G+B ? ?

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

10. 2 f 2 f ADDITIVE SYNTHESIS OF SPECTRAL LIGHTS

11. CENTER OF GRAVITY RULE Light Orange colour

13. CENTER OF GRAVITY RULE

14. 2 Barycentric Coordinates and mixing colour lights y r Y R balance scales

15. 3 Barycentric Coordinates and mixing independentcolour lights (R,G,B) r b g r g b Chromaticity Diagram r = R/(R+G+B) g = G/(R+G+B) b = B/(R+G+B) Barycentric Coordinates B G R

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

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

18. CENTER OF GRAVITY RULEconstraint among spectral lights METAMERISM

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

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

21. B + G - R = C ????? B + G = R + C = Q  METAMERISM + R G C B Q

22. METAMERISM … 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

23. … 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 NOTof the quantities of mixed orange and white powders, BUT the quantities of the lights reflected from them. I. Newton

24. COMPLEMENTARY COLOURS ?!?!?

25. COLORI COMPLEMENTARI COLORI COMPLEMENTARI ?!?!? COMPLEMENTARY COLOURS ?!?!?

26. 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 1800. 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.” Christian Huygens: (1673) – “two colours alone (yellow and blue) might be sufficient to yield white.”

27. Newton’s mistake and open problems: • 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 • all the Magenta hues are represented by a point in the colour circle • Circular shape is only an approximation

28. four independent colours are not existing!!TRICHROMACY

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

30. Grundig television

31. SUBTRACTIVE MIXING OF COLOURS in screen plate printing

32. Demichel (1924) – Neugebauer (1937) Additive mixing of 8 colourlights MAGENTA YELLOW CYAN RED BLUE WHITE GREEN BLACK

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

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

35. Towards the definitionofimaginaryprimaries 1757 –MikhailVasil’evichLomonosov 1777 – George Palmer 1780 – John Elliot MD1802 – Thomas Young(1840 – David Brewster)

36. REAL & IMAGINARY PRIMARIES X Z Y

37. George Palmer (1777)

38. Thomas Young(1802)(1817) • 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 (ClaudiusPtolomaeus ≈100 – 175)

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

40. -complementary colours- magenta hues- chromaticity diagram

41. REAL SPECTRAL PRIMARIES

42. IMAGINARY PRIMARIES Colour-Matching Functions in fundamental reference frame

43. - fundamental reference frame- imaginary primaries A R V

44. James Clerk Maxwell (1857)

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

46. Instrumental reference frameRed-Green-Blue real primaries Fundamental reference frame imaginary primaries Green Red Blue

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

49. Colour-Matching Functions: Maxwell’s minimum saturation Method R = 630.2 nm (rosso) G = 525.1 nm (verde) B = 456.9 nm (blu) Colour matching of two beams

50. Helmholtz-Hering controversy(1872)