Cathode-ray-tube to reflection-print matching under mixed chromatic adaptation using RLAB

Abstract

Color-appearance models are used to relate chromatic stimuli viewed under one set of viewing and illuminating conditions to a differing set such that when each stimulus is viewed in its respective conditions, the stimuli match in color appearance. These models assume the observer has a steady-state adaptation to each condition. In practice, observers often view stimuli under mixed adaptation; this could occur when viewing CRT and reflection-print stimuli simultaneously. A visual experiment was performed to determine whether the RLAB color-appearance model could be used successfully to generate reflection prints that match the appearance of the CRT when viewed under mixed states of adaptation and in turn as stand-alone images viewed under a single state of adaptation. Sixteen observers viewed four pictorial images displayed on a D65 balanced CRT display in a room lit with cool-white fluorescent luminaries. The RLAB color-appearance model was used to calculate corresponding images where the observer's state of chromatic adaptation was assumed to be one of the following: adaptation to each device condition, a single adaptation at the midpoint of the two device conditions, adaptation to the CRT condition and a print adaptation shifted 25% toward the CRT condition, adaptation to the print condition and a CRT adaptation shifted 25% toward the print condition, and a CRT condition shifted 25% toward the print condition and a print condition shifted 25% toward the CRT condition. Each condition was compared pairwise and Thurstone's law of comparative judgments was used to calculate interval scales of quality. Observers first judged the reflection prints adjacent to the CRT display selecting the image closest in color appearance to the CRT image; they also categorized the closest image as "acceptable, " "marginally acceptable, " or "not acceptable. " The images were again scaled except the display was turned off; this determined the best stand-alone color reproduction. The observers determined that images generated where it was assumed that the CRT adaptation was shifted 25% toward the print condition and a print adaptation was shifted 25% toward the CRT condition produced both the closest match to the CRT display and the best stand-alone image. The mixed-adaptation matches were acceptable or marginally acceptable on average 84% of the time. This adaptational condition produced the most preferred stand-alone images due to shifts toward regions of known preferred color reproduction.