Performance of lightness difference formulae

There are large variations between different previously published lightness difference experimental data sets. Two hundred and eight pairs of matt and glossy paint samples exhibiting mainly lightness differences were accumula ted. Each pair was assessed about twenty times by a panel of fourteen obser vers using the grey scale method. The results were used to derive a new lig htness difference formula (CII), and to a large extent, a new CIE lightness difference formula (CMC99). Both formulae were found to be more accurate t han the typical deviation of an individual assessment from the mean of a pa nel of 20 observers, and outperformed the existing formulae using the prese nt data set. The new CMC99 lightness difference formula is integrated into the new CIE colour difference equation CIEDE2000. The results also showed t hat special attention should be paid to measuring very dark samples. This i s caused by poor instrument repeatability and inter-instrument agreement in this colour region.