Color order system

INTRO

A technical committee of the International Organisation for
Standardisation, ISO/ TC187 (Colour Notations), has defined
a colour-order system as a set of principles
For the ordering and denotation of colours,
usually according to defined scales.

colour-order system is a set of principles that defines:
(a) an arrangement of colours according to attributes such that
the more similar their attributes, the closer are the colours located in
the arrangement, and
(b) a method of denoting the locations in the arrangement, and
hence of the colours at these locations.

INTRO

The purpose of a colour-order system determines
the number of attributes that must be considered,
each attribute defining one dimension of the system.

For example,
a one dimensional system may be adequate in the design of lighting
systems, where it is sometimes sufficient to consider only the single
attribute of CIE luminance factor (Y),

which is a function of the total reflectance of each surface within the
volume to be lit.

INTRO

Colour is three-dimensional, however, and for a complete colour
specification
a colour-order system such as that given by CIE x, y and Y is
necessary.

x, y and Y are attributes of a colour
and each is used to define a dimension of the system.

The dimensions are arranged by means of three mutually
perpendicular axes. The three attributes are
fundamental to the system because they define it,
 and they are orthogonal
(that is, each may be varied without having to change any other).

INTRO
We may however define a colour-order system by means of
The orthogonal attributes λd (or λc), pe and Y,
with x and y then being derived attributes.

Whether the system be defined by means of
x, y and Y,
or λd (or λc), pe and Y,
the relationships between colours in it are the same.

Each defines the same colour space, that is,
the geometric representation of colours in three dimensions .
any three-dimensional colour-order system necessarily defines
a colour space
and any colour space allows colours to be ordered.

DIFERENCE b/w color order system
and color space
a colour-order system is primarily defined by
a set of material colour standards,

whereas a colour space is essentially
a conceptual arrangement.

colour-order systems

Over the years, more than 400 colour-order systems have been compiled.

The first to be recorded was devised by Aristotle about 350 BC. It was vaguely
three-dimensional and white was placed opposite black; red, however, was
placed between black and white, red being the colour of the sky between the
states of night and day.

Leonardo da Vinci (1452–1519) is said to have painted sequences in which
closely related colours were placed near each other.

Newton (1642–1727), whose discovery of the nature of white light may be
regarded as having begun the science of colour physics, arranged all the hues in
a circle, with complementary hues opposite and white at its centre. These
arrangements were two-dimensional, however, and could not therefore include
all colours.

Munsell colour-order system:
concept
• Munsell apparently first described his system in a lecture
given in 1905 in which he listed its advantages, including:

• (a) colour names based on natural objects (which often vary
in colour) are replaced by a definite notation;

• (b) each colour is named by its notation and can be recorded
and transmitted by it, enabling contracts for coloration to be
closely specified;

• (c) the system can be expanded to accommodate new colours.

concept
• A model of the Munsell colour-order
system is shown in Plate 2.

• The three fundamental orthogonal
attributes defining the system are
called
• Munsell value V,
• Munsell chroma C
• and Munsell hue H.

concept
• A model of the Munsell colour-order
system is shown in Plate 2.

• Each is scaled with the aim of perceptual
uniformity, so that equal changes in any
one of the attributes represent the same
perceived difference in colour.

• Unlike the CIE xyY system, it uses
cylindrical coordinates;
• for readers meeting this coordinate system
for the first time, a brief explanation
follows. (In the following three
paragraphs, x and y are general variables,
• not CIE x and y.)

concept
• We are all familiar with two-
dimensional plotting of y against x,
 with the axes of x and y perpendicular
to each other (Figure 4.1).
 In this so-called rectangular coordinate
system,

• the point A = [2,2]
• (meaning x = y = 2) is located,
• relative to the origin (O =[0,0]),
 by measuring two units along the x-
axis to the point XA,
 and then from XA two units parallel
to the y-axis.

concept
• The location of A may alternatively
be specified using
 Polar coordinates,
 i.e. in terms of a distance and an angle.

• Taking the positive part of the x-axis
as a starting line,

• we may specify the location of A
unambiguously in terms of the
• distance OA
• and the angle in degrees between the
x-axis and OA,
• Conventionally measured
anticlockwise.

concept
• By Pythagoras’s theorem, the
distance
• OA = (22 + 22) = 81/2 units
• and the angle is 45°,

• so in a polar coordinate system we
write A = (81/2 ,45).

• In a polar coordinate system, a point
having one or both of its rectangular
coordinates negative is specified
using values of H > 90.
• Thus the point with rectangular
coordinates [–2, –2] becomes
(81/2,225) in polar form.

concept
• In the Munsell colour-order system,
we write the polar coordinates of
any point
• (B in Figure 4.1) as (C,H),

• where C is the distance OB
• and H is the angle OB
• makes with the positive part of the x-
axis.
• C and H are derived from the
rectangular coordinates x and y by Eqn
4.1:

concept
• Colour, however, is three-dimensional.

• In a rectangular coordinate system the
third dimension is introduced by
• adding a third axis, perpendicular to those
of x and y and passing through O.

• If exactly the same thing is done in a
polar coordinate system, it becomes
• a cylindrical coordinate system in which,
• by convention, the principal axis (OP) of
the cylinder is oriented vertically (Figure
4.2).

concept
• The general point is now
• D = (V,C,H),
• where V is the distance OL
• (L being the point where the principal
axis intersects the horizontal plane
containing the point D),

• C is the distance LD
• and H is measured anticlockwise from the
reference plane OPQR, bounded by the
principal axis.
• (Cylindrical coordinates, though perhaps
unfamiliar, have the ad making the
structure of colour space much easier to
work with; it is worth persevering
• with the concept.)

concept(V=0,10)
• In the Munsell system the vertical axis of the
cylinder is the V-axis.
• Its lower end (V= 0) represents the perfect black,
• a term often used to indicate a uniform reflectance of
0%,
• and its upper end (V = 10) an approximation to the
white of the perfect reflecting diffuser.

• The CIE defines the latter as the ideal isotropic
diffuser
• (that is, radiation reflected from it is equal in
intensity in all directions in the hemisphere in
which it occurs)
• with a uniform reflectance of 100% .

concept(V=0,10)
• The intermediate points on the V-axis
• represent the infinite number of
• achromatic colours (that is, colours that
resemble only black and white )

• corresponding, inter alia, to uniform
percentage reflectances of R
• (0 < R < 100),
 which are perceived as blacks (if R ≈ 0),
 whites (if R ≈ 100) and greys.

concept(V=0,10)
• All colours with a given V, whether achromatic or chromatic
(chromatic being the opposite of achromatic, that is, colours
possessing hue, even if only slightly ), fall on
• the horizontal plane that contains the given V.
• The V-coordinate of a coloured surface is determined by
• its lightness, which is a function of the total reflectance of the
surface, weighted according to the response of the human visual
system to stimuli of different wavelengths.

• The lightness of a colour is a measure of how it would
appear, for example, in a black and white photographic
print, provided all the processes leading to the print exactly
emulated the human visual process.
• If two colours, say an orange and a grey, appear identical in
such a print they have the same lightness, and hence the
same V.

concept(ELEMENTARY)
• elementary colour
• There are six such colours:
• white, black, red, yellow, green and blue.

• We may thus identify two elementary achromatic colours
• (white and black)

• and four elementary chromatic colours
• (red, yellow, green and blue).

concept(HUE)
• Hue is then defined as
 the attribute of a chromatic colour
according to which it appears to be
similar to one of the elementary
chromatic colours
or to a combination of two of them

concept(HUE)
• The Munsell system has
a qualitatively similar
hue circuit.

• It surrounds the
achromatic axis

• but it is a circle in
which equal steps do
correspond to visually
equal differences in hue.

concept (HUE)
• In it, the five so-called Munsell
principal hues –
1. red (R),
2. yellow (Y),
3. green (G),
4. blue (B)
5. and purple (P)
• are equally spaced around the
circle
• and arranged clockwise in the
order given when viewed from
‘above’ (Figure 4.3).

concept(HUE)
• Lying halfway between each pair of
adjacent principal hues

• is one of the five intermediate hues
• (YR, GY, BG, PB and RP).

• Together, the principal and
intermediate hues constitute the ten
major hues of the system.

• Each is subdivided into ten equal
parts,

• so that the whole circle is divided
into a total of 100 equal angular
intervals.

Munsil COLOR (Hue)
• The attribute of Munsell hue (H) may thus be specified by means of an
angular scale of 0 < H ≤ 100 with 100
• (equivalent to 0) representing a hue midway
• between RP and R,
 R itself being at H =5,
 YR at H = 15, and so on.
• More usually, however, a system is used in which one of the major hues is
given preceded by
• a number n (0 < n ≤ 10).
• If n = 5, the major hue itself is indicated (5R, for example, denotes the major
hue red).
• A designation of n > 5 implies
• a hue clockwise from the given major hue
• (and n < 5, anticlockwise); thus, for example, 7R denotes a red shade that is
yellower than the major red hue 5R

Munsil COLOR (Chroma)
• To define the significance of the dimension C of the Munsell
system, we return to the chromaticity diagram.

• The colours of the spectrum locus and the nonspectral purples
• resemble one of the elementary chromatic colours
• (or more usually only two adjacent ones).

• Most colours of a given lightness, however, also resemble that
• achromatic colour which has the same lightness.

Munsil COLOR (Chroma)
• An orange colour, say, may possess
(a) a full chromatic colour is a
• only the attributes of redness and
yellowness colour
• in a given ratio, that resembles only the
elementary chromatic
• whereas a brown which possesses colours, and (so) does not at
these two attributes in the same all resemble grey
ratio also has the attribute of
greyness. (b

• This leads us to two further
definitions:

The Munsell chroma (C) of a
colour dictates
• The Munsell chroma (C) of a colour dictates
• the distance from the achromatic axis
• At which it is placed in the system.

• It is a measure of the extent by which the colour
differs
• from the achromatic colour of the same V.

• The orange colour mentioned above has a
• higher C than the brown and hence lies further from
the achromatic axis,

• all truly achromatic colours having C = 0.

realisation
collection of coloured specimens
or colour atlas,
defined as the arrangement of
coloured specimens according to a colour-
order system

realisation
• On each chart chips are displayed at
intervals of
• V = 1 and C = 2,
• arranged with those in each row of
constant V
• and those in each column of constant
C (Figure 4.4).

• The inequality of the intervals of V
and C arises because although
• Munsell designed the three
fundamental attributes of his system
with the aim of perceptual
uniformity,
• he deliberately chose scales such that
V = 2C = 3H at C = 5.

realisation
• The scaling of H relative to that of
• V and C needs to be qualified
• (at C = 5) because

• Munsell colour space is specified by a
cylindrical coordinate system

realisation
• The chips of highest C on each Munsell constant-H
chart form a curved boundary,
• such as that in Figure 4.4,
• which is different for each chart. The boundaries of
each pair of adjacent charts are similar,

• however, so that all 40 boundaries form a smooth,
but
• irregular, three-dimensional locus
• called a colour solid: that is, a three dimensional
• representation of that part of colour space which
can be achieved by means of coloured objects .

realisation
• The chips of highest C on each Munsell constant-H

• In each hue chart, the chip of highest C
• for each V
• has a lower C than
• that of the optimal colour stimulus for this H and V.

• The C of real surface colours is necessarily lower
because

• they are produced using real colorants,
• which neither absorb nor reflect perfectly at all visible
wavelengths.

realisation
• Additionally, in any colour atlas the maximum
C illustrated is

• restricted by the need for the colour of the chips

• to be maintained throughout a production run,

• to be reproduced between runs,

• and to be stable to the various agencies to which
they are exposed during use.

COLOR SPACES
1. CIE xyY colour space
2. Judd triangular and MacAdam rectangular UCS diagrams
3. Hunter Lαβ and Scofield Lab colour spaces
4. Adams chromatic value colour space
5. Hunter Lab colour space
6. Adams–Nickerson (ANLAB) colour space
7. Early cube-root colour spaces
8. CIE 1960 UCS diagram and CIE 1964 (U*V*W*) colour space
9. CIE 1976 UCS diagram, CIELUV and CIELAB colour spaces
10. Residual non-uniformity of CIELUV and CIELAB colour spaces

Color order system

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