Colour difference acceptability for calibrated digital images

The aim of this research work is to establish what level of numeric colour difference between two digital images is visually acceptable by average hum an observers on a calibrated monitor under a fixed set of viewing condition s. A visual ordinal category method is introduced and a description of the experimental design is provided. Results based on over 4000 visual and nume ric comparisons are reported. All results are analysed by statistical metho ds. The correlation between visual assessments and numerical assessments ar e found by means of the Pearson product moment coefficient. Overall colorim etry accuracy and metamerism are discussed. A very high level of correlation is found to exist between the visual ordin al categories assigned by observers and the equivalent numeric (DeltaE CMC 2: 1) colour difference. Individual observers, within the group of 20 obser vers tested, were found to be consistent in their ordinal categories. Howev er, some observers were consistently severe in their judgement and others s ignificantly more lenient.