Investigation of parametric effects using large colour differences

Sixty-five wool sample pairs around eight colons centers were used to inves tigate the change of colour differences caused by four viewing parameters: lightness of background, sample separation, luminance, and magnitude of col our difference. The average size of colour difference was 13 CIELAB Delta E units. Each pair was assessed 20 times by a panel of 13 normal colour-visi on observers using the gray scale psychophysical method. The viewing parame ters investigated did not greatly affect the perceived colour difference. T he largest discrepancy was found between the gray and white background cond itions, i.e., the same pair of samples shows a 30% larger colour difference against a white background than against a gray background. The present res ults were also used to compare,vith those of the authors' earlier study(2) using small colour differences. It showed that there is a large difference in characteristics between the large and small colour differences. The visu al data were also used To test five colour-difference formulae: CIELAB, CMC , BFD, CIE94, and GLAB. The results showed that the GLAB formula, developed by the authors, performed marginally better than the other formulae. (C) 1 999 John Wiley & Sons, Inc.