Standards Development

Scope

This document specifies a method for the quantitative determination of small colour differences for object colours. The formula was developed using pairs of specimens with small colour differences E* 5. Colour difference determinations may, for instance, be the basis for agreements on limits for tolerable variations of coloured products during their industrial or commercial production. The method in this standard applies for coloured products (e.g. textiles, coatings, plastics, prints, glass) that are to be evaluated in pairs for colour conformity, and which have small perceptible colour differences.

Purpose

The DIN99o formula is an optimized version of the DIN99 formula in which the numeric parameters have been optimized using an international data set for identifying small colour differences. The form used in this context preserves the initial idea of the DIN99 formula based on the CIELAB colour coordinates. In the meantime, the CIE (International Commission on Illumination) has finalized a further optimization of parameters in the CIE94 formula and recommended it as CIEDE2000 (see ISO 11664- 6) for the calculation of small colour differences. The direct comparison of the DIN99o formula with the CIEDE2000 formula revealed good matches, with the results achieved using the DIN99o formula being only slightly worse.

The reason for adhering to the DIN99o formula despite the CIEDE2000 formula is the different structure of both formulas. The DIN99o formula is based on the transformation of the CIELAB coordinates and thus obtains the definition of a colour difference directly as the difference between two vectors in a colour space. Vectors are no longer of significance in the CIEDE2000 formula in which the optimization of weighted colour difference components uses the CIELAB colour space, even if a “vectorization” will be possible at a later point. ISO/TC 256 intends to further promote the international discussion with this initiative, particularly because efforts continue within the CIE to find a better colour space based on physiological parameters to calculate small colour differences. The DIN99o formula shows how such an approach is possible based on CIELAB coordinates. The ultimate goal is to base the evaluation of small colour differences on a single, internationally accepted formula. The discussion about retaining the CIELAB formula is influenced by new findings showing that the CIELAB formula does not evaluate large colour differences as poorly as it does small ones, and that it can possibly assert its position in that area. The reason for this difference is a nonlinear relationship between the perceived magnitude of the colour difference and its evaluation using a colour difference formula when progressing from small to large colour differences.differences. Therefore, it makes
sense to use different colour difference formulas for small and large differences.