LINEARITY AND ADDITIVITY OF SMALL COLOR DIFFERENCES

The functional relation of visual to colorimetric scaling of small col or differences is needed for, a realistic interpretation of the percep tual magnitude of a measured color difference. Linearity is usually as sumed and differences are expressed in threshold units without adjustm ent. An experimental plan is described that provides for the applicati on of gray-scale assessment to visual judgments under controlled param eters. Gray scale and test colors were produced from a two-component a crylic lacquer system. A green color center (CIE green) was chosen for a first test with color differences extending from the center in the directions of hue, saturation/chroma, and lightness in steps ranging f rom -5 to +5 thresholds. Thirteen observers made 4 judgments of each o f 78 color-difference pairs. The resulting scales were typically linea r but increasing less steeply than threshold stepping, however, F-stat istics showed some inhomogeneous effects. Scales along the main color directions tended slightly to subadditivity. The vector model of color difference better predicted the magnitude of diagonal jumps between t wo color directions than did the city-block model. Relations to some r ecent color-difference formulae were studied and the CIE TC1-29 formul a was found to be a good predictor for this color center. (C) 1995 Joh n Wiley & Sons, Inc.