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DIN 6174

2007 Edition, October 2007

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Colorimetric evaluation of colour coordinates and colour differences according to the approximately uniform CIELAB colour space

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Superseded By: DIN EN ISO 11664-4

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Description / Abstract:

In the colour industry, colour differences (see definition in DIN 5033-1) are increasingly being described by means of colour coordinates. Since these coordinates - which describe the magnitude of the perceived colour difference between two samples (e.g. between a colour target and a colour match) - are not derived from the Euclidean distance within the standard colorimetric system, over the years various empirical colour distance formulae have been developed and are used.

This standard defines a method of calculating the colour coordinates L*, a*, b* of the approximately uniform CIE 1976 (L* a*b*) colour space (referred to below as the CIELAB colour space) (see clause 4) on the basis of the tristimulus values X, Y, Z of the visually non-uniform colour space described by the standard colorimetric system. It also describes how colour differences, particularly object colours, can be quantitatively described using colour difference formulae (see clause 7); such differences occur, for instance, when coloured products are influenced by chemical or physical factors, when matching colours, or when a product has a non-uniform colour. The determination of colour differences can serve as the basis of agreed colour tolerances.

In many ways, the CIELAB colour coordinates have become widely accepted as a means of indicating colours in industry, especially as regards image processing.

The colour difference formulae given here are to be used especially for object colours (e.g. of textiles, paints, plastics, glass, and printed documents). However, the formulae do not evaluate small differences in various areas of the colour space in a uniform manner, i.e. colour differences which are visually perceived as being the same may have different corresponding CIELAB differences. Improved formulae which describe the coordinates of the CIELAB colour space in a more uniform manner are given in DIN 6176, for instance, or in CIE 15:2004 "Colorimetry"; these formulae were developed for standard illuminant D65.

Because of different mathematical definitions, colour differences determined on the basis of different formulae are as a rule not linearly convertible, and therefore the particular colour difference formula used shall always be given.