BFD (l:c) colour‐difference formula Part 2‐Performance of the formula

The available experimental data relating to small colour differences between pairs of surface colours have been combined together into two sets including perceptibility results (CP) and acceptability results (CA). A new colour‐difference formula, BFD(\:c) has been developed using the combined experimental results. For small colour differences, particularly when perceptibility judgements are involved, the new formula represents a substantial improvement over other fomulae. For large colour‐differences the new formula is close to the best available formula. Different 1 values are required for perceptibility and acceptability judgements, and for large colour differences, but c=1 in all cases. The BFD formula gives the best possible results obtainable with currently available data. Analysis shows that results from different studies, including those based on perceptibility and acceptability judgements, are compatible in many respects. Discrepancies that were detected seemed to be due to experimental error, or problems in scaling the visual results. However, there are major differences between the results for small differences between surface colours and those implicit in the Munsell system and MacAdam ellipses.