The quantification of small visual colour differences

The Shademaster system, developed at UMIST, was used to explore the use of on‐screen colour in order to assess the reliability of the CMC (l:c) formula as a measurement of small colour differences. Differences limited to almost pure hue, chroma and lightness changes around nine colour centres were judged by a group of ten observers. Each colour difference pair was presented on‐screen in the form of a divided tile. The colour difference between each pair was measured using a Bentham telespectroradiometer and by a method using reverse transformation of RGB to CIE coordinates. The resultant measurements were used to determine the visibility of a particular colour difference, how that visibility varied from colour to colour and how it varied in different directions (i.e. hue, chroma or lightness). The data obtained from the judgements were used to construct perceptibility boundaries around each colour centre.