A Concise History of the Chromaticity DiagramA Concise History of the Chromaticity Diagram

from Newton to the CIE from Newton to the CIE Standard Colorimetric Standard Colorimetric Observer Observer

Claudio OleariDipartimento di FisicaUniversità di Parmaclaudio.oleari@fis.unipr.it

CREATE 2010, Gjøvik

I am not an historian

(but I like History) !

warningAll phenomena that follow hold true

for colour matching in

aperture mode.

!

The protagonists

1623 - Galilei

1704 - Newton

1802 - Young

1808 - (Göthe)

1852 - Helmholtz

1853 - Grassman

1857 - Maxwell

1872 - Hering

1920 - Schrödinger1931 ...

The historical steps

centre of gravity rule

three kind of photoreceptors (fibres)

tristimulus: colour measure in ZERO ORDERZERO ORDER approximation

The standards CIE 1931-CIE 1964-CIE 1976The standards CIE 1931-CIE 1964-CIE 1976OSA-UCS system (1947-1974)

“Colour Appearance”: towards the colour measure in FIRST ORDERFIRST ORDER approximation

(Göthe against Newton)

Helmholtz-Hering Controversy

trichromacy trichromacy Le Blom, Palmer

Indeed, rays, Indeed, rays, properly expressed, properly expressed, are not coloured.are not coloured.

(Isaac Newt(Isaac Newton) on)

Any colour computation needs colour Any colour computation needs colour measurement.measurement.

But But ColourColour is a sensationis a sensation..

Then the question:Then the question:

Can colour be measuredCan colour be measured??

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.

?

colour matching in bipartite field

R+G+B

?

B

G

R

?

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)EXPERIMENTUM CRUCIS (1671)

No individual ray, no single refrangibility, is corresponding to white.

White in a heterogeneous mixture of differently refrangible rays.

ADDITIVE SYNTHESIS OF SPECTRAL LIGHTSADDITIVE SYNTHESIS OF SPECTRAL LIGHTS

2 f 2 f

CENTER OCENTER OFF GRAVITGRAVITYY RULERULE

Light Orange colour

CENTER OF GRAVITCENTER OF GRAVITY Y RULERULE

R Y

ry

Barycentric Coordinates and mixing Barycentric Coordinates and mixing colour lights colour lights

balance scales

2 2

R r

Y y

brg

(R,G,B)B

R

G

rg b

Chromaticity Diagram r = R/(R+G+B) g = G/(R+G+B) b = B/(R+G+B)

Barycentric CoordinatesBarycentric Coordinates

Barycentric Coordinates and mixing Barycentric Coordinates and mixing

independent colour lights33

: : : :R G B r g b

Three lights are independent if none of these lights is matched

by a mixture of the other two lights.

Barycentric Coordinates and mixing Barycentric Coordinates and mixing 44

independent (?)independent (?) colour lightscolour lights

Can we use a three dimensional yoke in a four Can we use a three dimensional yoke in a four dimension spacedimension space

NO!NO! Because Because four independent four independent colours are not existing!!colours are not existing!! TRICHROMACY TRICHROMACY

??

CENTER OF GRAVITCENTER OF GRAVITY Y RULERULE

constraint among spectral lights METAMERISMMETAMERISM

TRICHROMATIC COLOR RIPRODUCTION TRICHROMATIC COLOR RIPRODUCTION & REAL PRIMARIES& REAL PRIMARIES

R

B

G

An RGB system cannot reproduce all the real colours!An RGB system cannot reproduce all the real colours!

Instrumental reference frame

B

G

Negative light source!?!?

CB + G R = C ?????B + G = R + C

Phenomenon explained by Maxwell 180 years later

R

B

G

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

C

METAMERISMMETAMERISM

R

Q

… 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

METAMERISMMETAMERISM

… 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 NOTNOT of the quantities of mixed orange and white powdersmixed orange and white powders, BUTBUT the quantities of the lights reflected lights reflected from them. I. Newton

COMPLEMENTARY COLOURS ?!?!?COMPLEMENTARY COLOURS ?!?!?

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

The existence of pairs of spectral lights that can be mixed to match white (complementary spectral lightscomplementary 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 colourfaint 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 blueyellow and blue) might be sufficient to yield white.”

Newton’s mistake Newton’s mistake and open problems:and open problems:

1)1) angular position of the spectral lights angular position of the spectral lights ((Primary ColoursPrimary Colours) on the colour circle are ) on the colour circle are in relation to the in relation to the musical notes musical notes and not to and not to the colour complementaritythe colour complementarity

2)2) all the all the MagentaMagenta hues are represented by a hues are represented by a point in the colour circlepoint in the colour circle

3)3) Circular shapeCircular shape is only an approximation is only an approximation

four independent colours four independent colours are not existing!!are not existing!! TRICHROMACY TRICHROMACY

ADDITIVE MIXING OF COLOURED LIGHTSADDITIVE MIXING OF COLOURED LIGHTS

R

B

G

R

G

B

rgb

Grundig television

SUBTRACTIVE MIXING OF COLOURS SUBTRACTIVE MIXING OF COLOURS in screen plate printingin screen plate printing

CYANYELLOW

MAGENTA

BLUEGREEN

RED

BLACK

WHITE

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

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

TRICHROMACY of colour mixture: TRICHROMACY of colour mixture:

impalpable trichromacy impalpable trichromacy ↔ ↔ ↔ ↔ material trichromacymaterial trichromacy

- TRICHROMACY- TRICHROMACYand development of and development of three-colour reproductionthree-colour reproduction

- TRICHROMACY - TRICHROMACY in opposition to Newton’s opticsin opposition to Newton’s optics

Towards the definition of imaginary primaries

1757 – Mikhail Vasil’evich Lomonosov1777 – George Palmer1780 – John Elliot MD1802 – Thomas Young(1840 – David Brewster)

REAL & IMAGINARY PRIMARIESREAL & IMAGINARY PRIMARIES

Z

Y

X

George Palmer George Palmer (1777)(1777)

• 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 YoungThomas Young (1802)(1817)(1802)(1817)

Hermann von Helmholtz

(1852)(1855)(1866)

-- complementary colourscomplementary colours- magenta hues- magenta hues- chromaticity diagram- chromaticity diagram

REAL SPECTRAL PRIMARIESREAL SPECTRAL PRIMARIES

IMAGINARY PRIMARIESIMAGINARY PRIMARIES

Colour-Matching Functions in fundamental reference frame

R

V

A

- fundamental reference frame- imaginary primaries

James Clerk Maxwell

(1857)

Dpt Exp.Psychology, Cambridge University

Check of Newton’s centre of gravity rule

R

B

G

trilinear mixing triangle (c.1860)

Red

Green

Blue

Instrumental reference frameRed-Green-Blue real primaries

Fundamental reference frame imaginary primaries

)(b)(g

)(r

(K = Katherine)

Colour-matching functions in instrumental reference frame

CIE 1931 observer

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 beamsColour matching of two beams

Helmholtz-Hering controversy

(1872)

Ervin Schrödinger

(1920)

- fundamental reference frame,- “Helligkeit” equation and Alychne - tristimulus space metrics

- Hering’s chromatic opponencies

Ervin Schrödinger (1920)

tristimulus space and fundamental reference frame

Chromaticity diagram

König’s Colour-matching functions or König’s fundamentals

Lv=eRR+eGG+eBB

Exner’scoefficients

(R, G, B) (eR, eG, eB)

Schrödinger’s “Helligkeit” equation

LUMINANCE

towards the Colourimetric Standard Observer CIE

1931

X

Y

Z alychnealychne

700

400

500

600

)(z

Standard Colourimetric Observer CIE 1931Standard Colourimetric Observer CIE 1931

(D. B. Judd introduced the Schroedinger’s alychne)

)(x

)()( Vy

alychnealychne

From Newton to From Newton to SchSchrrödidinger & Juddnger & Judd

q1 q2q

W1 W2

q1q2

q

Alychne

( , )

( , )

q

q

x y

x y1 1 1

2 2 2

( , ) ,

x W x W y W y Wx y x y

W W W W1 1 2 2 1 1 2 2

1 2 1 2q

CENTER OF GRAVITCENTER OF GRAVITYY RULE RULE

Newton 1671 (1704) CIE 1931

CENTER OF GRAVITCENTER OF GRAVITYY RULE RULE

Thank you for your kind attention

Claudio Oleari

König’s Colour-matching functions or König’s fundamentals

Chromaticity diagram

tristimulus space and fundamental reference frame