An evaluation of colour differences and tolerances in soft proofing

The perceptibility and acceptability of colour differences in soft proofing were evaluated in psychometric experiments. In the first part of the study the perceptibility and acceptability of colour differences between systematically modified versions of photographic images displayed on an LCD monitor were examined. An interval scale of perceived colour differences was derived from the results of a paired comparison experiment. The acceptability threshold for the colour differences of a contract proof was located on that scale based on the results of a category experiment. Significant but incomplete correlation was found between the perceived colour differences and predictions of colour difference equations, as calculated from the instrumental measurements of uniform colour patches. The threshold of acceptability corresponded to approximately 2 CIELAB ƒ´E units on average, but the threshold depended considerably on the image content and the type of modifying function. Furthermore, the magnitude and acceptability of colour differences between proofs produced by two commercial soft-proofing systems and the corresponding reference prints were judged visually in another set of psychometric experiments. The results were comparable to the results of an earlier study with hardcopy proofs, and the proofs of the both soft-proofing systems were on average found to be sufficiently close in appearance to the reference prints to be acceptable as contract proofs.