Colour difference formulae

In principle, the higher the order of polynomial used, the more accmate the colour space transformation. However, there are some important parameters to be considered the material of the test target, the number of colours used for deriving the transform coefficients and their distribution throughout the colour space. The predicted error between the measured and predicted tristimulus values can be calculated using a colour difference formula such as CIELAB (CIE 15.2, 1986). 

CIE Draft Standard DS 014-6/E 2012, Colorimetry - Part 6 C1EDE2000 Colour-Difference Formula... 

In 1994 following extensive studies by the Colour Measurement Committee (CMC) the CIE94 total colour-difference was defined. In the equation, lightness, chroma and hue are weighted and corrected to account for variation in perceived colour magnitude and for sensitivity and variation in experimental conditions. Recently, the most prominent UK workers in the area of colour equation development combined under a technical committee to determine a generalised and reliable formula (Luo et al. 2000). They have also come up with an equation... 

Indicators are used in acid-base titrations as they change colour at i reaction. Indicators are usually weak acids in which the colour of the acid is different from that of its conjugate base. If we represent the Indicator as a weak acid of formula HIn, and say it has a red colour, and its conjugate base as In", and say it has a blue colour, its dissociation in water can be represented as Hln(aq) + HjO(l) H30" (aq) + In"(aq)... 

The dressing and colour may be distributed to the different fibres and the corresponding amounts of moisture allotted to these by direct application of the general formulae VI, where x3, xt and x3 represent respectively the percentages of cotton, wool and silk. The last may also be calculated by difference. 

Chromicyanides, manganicyanides, cobalticyanides, ruthenocyanides, and osmocyanides, are also known, similar in formulas to the ferro- and ferri-cyanides. On the other hand, nickel and platinum form double cyanides similar in formula to K2Pt(CN)4. The platinum salts are very beautiful, possessing the property of dichroism, i.e. of transmitting light different in colour from that which the crystals reflect moreover, only some of the facets of the crystals have this property. 

There are other minor nonequivalencies of ISO test procedures compared to ASTM standards, but for color difference the ISO Test Procedure No. 105 is unique. Those who use Colour Measurement Committee (CMC) procedures—particularly CMC 2 1 Lightness to Color ratio—claim that it facilitates a uniform description for acceptability decisions that is better than any other system in existence. These equations permit the use of a single number tolerance, DEcmc, in a nearly uniform color space. The CMC formula is a modification to the perceptibility CIELAB formula. It is fully described elsewhere in this book, but it deserves some brief notice here because, after all, it is an ISO procedure. The CMC developed the basic British Standard No. 6923, Calculation of Small Color Differences. Soon afterward, in 1989, the American Association of Textile Chemists and Colorists (AATCC) adopted AATCC Test Method 173, CMC Calculation of Small Color Differences for Acceptability. Ford Motor Company indicated a preference for using CMC 2 1 ratio color difference for plastics weathering data for plastics interior trim materials. 

The series of dyes represented by the formula in Fig. 10.1 exhibit different colours depending on the nature of the substituent X. These can be quantified in terms of the wavelength at which most light is absorbed, as shown in the following table. 

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