Large Colour Differences in Colour Reproduction – The Relationship Between Print Acceptability and Colour Difference

The formulation of a metric to provide numbers that correlate with visually perceived colour differences has proved a very difficult task. Most early experimental work was concerned with just-perceptible colour differences. Later the concept of perceptibility was expanded to acceptability, it being argued that many industrial tolerances were larger than just-perceptible. This leads naturally to the concept of large colour differences and the question as to whether the current CIE colour-difference formulae, specified as appropriate for just-perceptible differences, can be applied to the large differences experienced in the colour reproduction industry. This paper investigates the accuracy required of a large colour-difference metric as applied to photographic colour reproduction. It is shown that, within the limits imposed by a forced-choice experiment, the CIELAB colour difference of a scene element compared to its reference, is proportional to the percent acceptability of that scene.