A Concise History of the Chromaticity Diagram
from Newton to the CIE
Standard Colorimetric
Observer
Claudio Oleari
Dipartimento di Fisica
Università di Parma
claudio.oleari@fis.unipr.it
CREATE 2010, Gjøvik
I am not an
historian
(but I like History)
warning
All phenomena that follow hold true
for colour matching in
aperture mode.
The historical steps
The protagonists
1623 - Galilei
centre of gravity rule 1704 - Newton
trichromacy
Le Blom, Palmer
three kind of photoreceptors (fibres) 1802 - Young
(Göthe against Newton) 1808 - (Göthe)
1852 - Helmholtz
tristimulus: colour measure in ZERO ORDER 1853 - Grassman
approximation 1857 - Maxwell
Helmholtz-Hering Controversy 1872 - Hering
1920 - Schrödinger
The standards CIE 1931-CIE 1964-CIE 1976 1931 ...
OSA-UCS system (1947-1974)
“Colour Appearance”: towards the colour
measure in FIRST ORDER approximation
Indeed, rays,
properly expressed,
are not coloured.
(Isaac Newton)
Any colour computation needs colour
measurement.
But Colour
is a sensation.
Then the question:
Can 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
B
G
R
?
R+G+B
?
?
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
ADDITIVE SYNTHESIS OF SPECTRAL LIGHTS
2f
2f
CENTER OF
GRAVITY
RULE
Light Orange
colour
CENTER OF GRAVITY RULE
2
Barycentric Coordinates and mixing
colour lights
y
r
R r

Y
y
R
Y
balance scales
3
independent colour lights
Barycentric Coordinates and mixing
r
g
b
B
G
(R,G,B)
R
r b
g
R:G : B  r : g :b
Chromaticity Diagram
r = R/(R+G+B)
g = G/(R+G+B)
b = B/(R+G+B)
Barycentric Coordinates
Three lights are independent
if none of these lights is matched
by a mixture of the other two lights.
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
CENTER OF GRAVITY RULE
constraint among spectral lights

METAMERISM
TRICHROMATIC COLOR RIPRODUCTION
& REAL PRIMARIES
R
G
B
Instrumental reference frame
An RGB system cannot reproduce all the real colours!
-R
Negative light source!?!?
G
B
B + G - R = C ?????
C
B + G = R + C Phenomenon explained by Maxwell 180 years later
B + G - R = C ?????
B+GR+C=Q 
METAMERISM
+R
G
C
B
Q
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
… 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
COMPLEMENTARY COLOURS ?!?!?
COLORI
COLORI
COMPLEMENTARY
COMPLEMENTARI
COMPLEMENTARI
COLOURS
?!?!??!?!?
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.”
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
four independent colours
are not existing!!
TRICHROMACY
ADDITIVE MIXING OF COLOURED LIGHTS
b
g
r
R
G
G
B
R
B
Grundig television
SUBTRACTIVE MIXING OF COLOURS
in screen plate printing
Demichel (1924) – Neugebauer (1937)
Additive mixing of 8 colour lights
MAGENTA
YELLOW
CYAN
RED
BLUE
GREEN
WHITE
BLACK
Demichel (1924) – Neugebauer (1937)
Additive mixing of 8 colour lights
TRICHROMACY of colour mixture:
impalpable trichromacy ↔
↔ material trichromacy
- TRICHROMACY
and development of
three-colour reproduction
- TRICHROMACY
in opposition to Newton’s optics
Towards the definition
of imaginary primaries
1757 – Mikhail Vasil’evich Lomonosov
1777 – George Palmer
1780 – John Elliot MD
1802 – Thomas Young
(1840 – David Brewster)
REAL & IMAGINARY PRIMARIES
X
Z
Y
George Palmer
(1777)
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 (Claudius
Ptolomaeus ≈100 – 175)
Hermann
von Helmholtz
(1852)(1855)(1866)
- complementary colours
- magenta hues
- chromaticity diagram
REAL SPECTRAL PRIMARIES
IMAGINARY PRIMARIES
Colour-Matching Functions in fundamental reference frame
- fundamental reference frame
- imaginary primaries
A
R
V
James Clerk Maxwell
(1857)
Check of Newton’s centre of gravity rule
R
G
B
trilinear mixing triangle (c.1860)
Dpt Exp.Psychology, Cambridge University
Instrumental reference frame
Red-Green-Blue real primaries
Green
Fundamental reference frame
imaginary primaries
Red
Blue
Colour-matching functions
in instrumental reference frame
r ( )
b ( )
g ( )
CIE 1931 observer
(K = Katherine)
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
Helmholtz-Hering
controversy
(1872)
Ervin Schrödinger
(1920)
Ervin Schrödinger (1920)
- fundamental reference frame,
- “Helligkeit” equation and Alychne
- tristimulus space metrics
- Hering’s chromatic opponencies
tristimulus space and
fundamental reference frame
Chromaticity diagram
König’s Colour-matching functions or König’s fundamentals
LUMINANCE
(R, G, B)
(eR, eG, eB)
Schrödinger’s
“Helligkeit”
equation
Lv=eRR+eGG+eBB
Exner’s
coefficients
towards the Colourimetric
Standard Observer CIE
1931
Standard Colourimetric Observer CIE 1931
(D. B. Judd introduced the Schroedinger’s alychne)
z ( )
Y
y ( )  V (  )
x ( )
500
600
700
400
Z
alychne
X
From Newton to
Schrödinger & Judd
alychne
CENTER OF GRAVITY RULE
q1
q1
q
q2  ( x2 , y2 )
q2
q2
Alychne
q1  ( x1 , y1 )
q
W1
W2

x1W1 + x2W2
y1W1 + y2W2 
q  ( x, y )   x 
,y 

W1 + W2
W1 + W2 

CENTER OF GRAVITY RULE
Newton 1671 (1704)
CIE 1931
Thank you for your kind
attention
Claudio Oleari
Chromaticity diagram
tristimulus space and
fundamental reference frame
König’s Colour-matching functions or König’s fundamentals