Regression analysis to determine the optimum colour tolerance level for instrumental shade sorting

An investigation of the correlation between visual colour assessment and in strumental colour acceptance determination using regression analysis has be en carried out. Three colour-difference equations, CIELAB, CMC(2:1) and CIE 94(2:1:1), were studied in order to determine which is the best for generat ing a uniform colour space/microspace for allocating the colour population in shade sorting. Determination of optimum colour tolerance for further sha de sorting was also undertaken. Some 1320 pairs of dyed samples distributin g around 20 shade standards were measured instrumentally and also evaluated visually by a panel of 32 observers. Percentage rejection was plotted agai nst colour difference and different mathematical regression relationships w ere then imposed. As a result, both CMC and CIE94 showed better correlation between the two colour assessment methods than the CIELAB colour-differenc e equation. Consequently, optimum colour tolerance limits were determined f or subsequent development of shade sorting, with the findings being equally applicable to colour acceptance (shade passing).