Colour space, three dimensional

Uniform color scale n. A scale wherein the units of color difference that are judged to be equal have equal scale differences. McDonald R (1997) Colour physics for industry, 2nd edn. Society of Dyers and Colourists, West Yorkshire, England. Uniform color space Three-dimensional space wherein all pairs of colors, judged to be equally different, are separated by nearly equal distances. 

When colour is assessed on the basis of reflectance measurements, it is common to consider the three relevant attributes of perception of colour as hue, chroma (or saturation) which is the colourfulness or richness of the colour, and lightness, which refers to the amount of reflected light. These three attributes may be described using the concept of colour space, which shows the relationships of colours to one another and which illustrates the three-dimensional nature of colour, as portrayed in Figure... 

The system used by colourists in the dyes and pigments industry is the so-called CIELAB system. [Note CIELUV is the one used in the display industries (Chapter 3).] In this system the three-dimensional nature of colour space is taken into account namely hue (the colour attributes), saturation (the absence of white grey of black) and lightness (also called brightness). In CIELAB colour space the coordinate L is a measure of hghtness-darkness, where a perfect black is 0 i.e. zero whiteness) and a perfect white is 100 a correlates with red (-Ea ) and green (-a ) and b with... 

Barnard K, Martin L and Funt B 2000 Colour by correlation in a three dimensional colour space In Proceedings of the 6th European Conference on Computer Vision, Dublin, Ireland (ed. Vernon D), pp. 375-389. Springer-Verlag, Berlin. 

The aim of the more popular of the colom scales is to represent colours in a three-dimensional colom space, such that similar visual colom difieiences are represented by approximately similar distances in the colom space. Such colour scales are known as uniform scales. The original CIE scales, represented diagrammatically in Fig. 5.3, were not intended for identifying the colours of objects and are certainly not uniform in spacing colours according to their visual differences. Over the last forty years the Commission Internationale de I Eclairage (CIE) in particular have worked to try to stem the confusion caused by the presence of the many formulae in use and standardise colom space. They managed to combine the opponent chromatic attributes used by Hunter and Schofield, with the MacAdam cube-root simplification of the earlier Judd polynomial. The result was the publication of CIELAB (or ClEL a b ) in 1976 (Smith 1997). At this point, the asterisk snperscript was introduced in order to differentiate the CIELAB parameters from other similar ones still in use. 

We have already seen that trypsin, chymotrypsin and thrombin have very similar 3D structures. If we now overlay the three-dimensional structures of these enzymes we find that identical amino acids are found at many positions in space, including the active site serine, hrstidine and aspartic acid residues, as shown in Figure 10.11 (colour plate section). The amino acid sequences of these proteins can be arranged into a sequence alignment as... 

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