||H30: Specification of
Colour, Munsell and NCS> The most useful methods of
specifying the colour appearance of an object or a surface are those
that do not lead to confusion and where the method has a clear
interpretation. In this section we will be looking at the way that
colours can be specified by selecting samples from a colour atlas which
forms part of a colour order system. The Munsell and the NCS colour
order systems are described.
Putting Numbers to Colour: CIE RGB> Numerical methods
of describing colour communicate colour information without the need
for physical samples. Ideally the numbers should by easily interpreted
in terms of attributes such as lightness, chroma or hue. The RGB system
adopted by the CIE (Commission Internationale de l'╔clairage) in the
1930's is based on the principles of additive mixing of coloured lights
and the trichromatic theory of colour vision.
Putting Numbers to Colour: CIE X Y Z> In 1931, the 8th
session of the Commission Internationale de l' Eclairage (CIE) held in
Cambridge, England, devised a system that provided numerical
specificatio for all visible colours. This was based on defining a new
set of additive primaries X, Y, and Z based on the R G B set defined in
the CIE RGB system.
Putting Numbers to Colour: CIE L*a*b*> For practical
day to day application the CIE L* a* b* system has become the accepted
method of representing the appearance of surface colours . CIE L*a*b*
colour space was introduced in 1976 and the structure is based on the
opponent theory of colour vision.
Numbers to Colour: sRGB>In the
community of devices and industries that communicate colour information
with R G
B, there are many confusing and often incompatible R G B practices and
standards. Exactly which colour is represented by the R G B data stored
in an image file is not well defined. The objective of sRGB is to
provide a workable solution that solves most of the colour
communication problems for office, home and web users.
Assessment of Colour Difference> The link between
colour impression and product quality is very strong especially in a
prestige product. It can be expensive to correct the colour of an
off-shade finished product, not just in terms of wasted materials but
also in terms of the time involved. The most reliable visual judgement
of the colour of a material is made by a direct, side-by-side
comparison of the colour of the test panel with the colour of the
Instrument Assessment of Colour Difference> Instrument
methods of judging the colour appearance measure the colour
co-ordinates of the test and of the standard panel and then determine
the total colour difference dE*, and the component differences dL*
(lightness) dC* (intensity of colour) and dH* (hue).
of Colour> Instrument based
methods is becoming normal practice for the assessment of the colour
and colour difference of flat, uniform surfaces. The use of
microprocessor chips and the developments in optics has meant that the
size, ease of use and the performance of the instruments have improved
dramatically and the cost has been reduced.