An evaluation of small color difference in color matching

抄録

In every industry where color is important to the product, the routine evaluation of small color differences for the matching of similar materials has been generally carried out by skilled visual assessment. The Japan Color Research Institute (JCRI for short), however, depends on colorimetric evaluation using the color difference formula devised by Adams and Nickerson (ANLAB-40 for short). When correcting the color of the specimen, most color-matchers will want to know about the deviation from the reference, its direction and bias. For this purpose, a card indicating a small area of the ANLAB-40 color space is used. On this card, the narrow area around the reference is enlarged. It is possible to determine geometrically the direction and the bias of the specimen from the reference by using the card. Taking the opportunity when the CIE 1976 (L^*a^*b^*) color space (CIELAB for short) was provided, JCRI changed the color space from ANLAB-40 to CIELAB for use in colorimetric evaluation. Thus, as the quintic expression table is not used in the process of calculation, misreadings can be avoided completely. Furthermore, JCRI modified CIELAB to avoid the way by which the differences of hue, lightness and saturation were read graphically. The coefficients of suitable quantities were multiplied by a^* and b^*. Recently, colorimetric evaluation for color matching at JCRI has depended only on numerical specifications obtained by computer without the need for any manual or graphical process.