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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. |
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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'Éclairage) in the 1930's is based on the principles of additive
mixing of coloured lights and the trichromatic theory of colour vision. |
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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.. |
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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. |
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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. |
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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 sample
panel. |
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Instrument based 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). |
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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. |
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