INTROA technical committee of the International Organisation forStandardisation, ISO/ TC187 (Colour Notations), has defineda colour-order system as a set of principlesFor 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 thatthe more similar their attributes, the closer are the colours located inthe arrangement, and(b) a method of denoting the locations in the arrangement, andhence of the colours at these locations.
INTROThe purpose of a colour-order system determinesthe 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 lightingsystems, where it is sometimes sufficient to consider only the singleattribute of CIE luminance factor (Y),which is a function of the total reflectance of each surface within thevolume to be lit.
INTROColour is three-dimensional, however, and for a complete colourspecificationa colour-order system such as that given by CIE x, y and Y isnecessary.x, y and Y are attributes of a colourand each is used to define a dimension of the system.The dimensions are arranged by means of three mutuallyperpendicular axes. The three attributes arefundamental to the system because they define it, and they are orthogonal(that is, each may be varied without having to change any other).
INTROWe may however define a colour-order system by means ofThe orthogonal attributes λd (or λc), pe and Y,with x and y then being derived attributes.Whether the system be defined by means ofx, 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 definesa colour spaceand any colour space allows colours to be ordered.
DIFERENCE b/w color order system and color spacea colour-order system is primarily defined bya set of material colour standards,whereas a colour space is essentiallya conceptual arrangement.
colour-order systemsOver 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.
Munsell colour-order system: 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.
Munsell colour-order system: 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.)
Munsell colour-order system: 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.
Munsell colour-order system: 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.
Munsell colour-order system: 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.
Munsell colour-order system: 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:
Munsell colour-order system: 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).
Munsell colour-order system: 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.)
Munsell colour-order system: 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% .
Munsell colour-order system: 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.
Munsell colour-order system: 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.
Munsell colour-order system: 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).
Munsell colour-order system: 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 coloursor to a combination of two of them
Munsell colour-order system: 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.
Munsell colour-order system: 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).
Munsell colour-order system: 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.
Munsell colour-order system: realisation collection of coloured specimens or colour atlas, defined as the arrangement ofcoloured specimens according to a colour- order system
Munsell 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.
Munsell colour-order system: 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
Munsell colour-order 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 .
Munsell colour-order system: 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.
Munsell colour-order system: 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 SPACES1. CIE xyY colour space2. Judd triangular and MacAdam rectangular UCS diagrams3. Hunter Lαβ and Scofield Lab colour spaces4. Adams chromatic value colour space5. Hunter Lab colour space6. Adams–Nickerson (ANLAB) colour space7. Early cube-root colour spaces8. CIE 1960 UCS diagram and CIE 1964 (U*V*W*) colour space9. CIE 1976 UCS diagram, CIELUV and CIELAB colour spaces10. Residual non-uniformity of CIELUV and CIELAB colour spaces