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The available experimental data relating to small colour differences between pairs of surface colours have been combined together into sets including perceptibility results and acceptability results. Supplementary experiments have been carried out to enable all the previous visual results to be brought on to a common scale, and to provide extra information when this was considered necessary. A new colour‐difference formula, BFD(l:c), has been developed using the combined experimental results. Various aspects of colour differences have been considered in turn to decide the form of formula required, and the constants in the formula have been optimised using the combined perceptibility and acceptability results. The new formula is similar in structure to the CMC(l:c) formula in most respects. However, it was found that a new term was required to take account of the fact that when chromaticity discrimination ellipses calculated from experimental results are plotted in a b space, they do not all point towards the neutral point. The experimental results were not very consistent with respect to possible tilting of discrimination ellipsoids relative to the xy plane. Overall it seems that any such tilting is quite small and in the direction implicit in the CMC and BFD formulae. Experimental results based on both acceptability and perceptibility judgements form part of the same overall pattern except for the weighting of lightness differences relative to hue and chroma differences.
Luo et al. (Sun,) studied this question.