Specification of just-noticeable color difference for 2° and 10° stimuli using different color matching functions

Just-noticeable color difference (JNCD) is important in color specification and characterization. The commonly referenced specification of JNCD (i.e., 0.004 or 0.0033 u′v′ unit) is thought to originate from the MacAdam ellipses, which were derived using 2° color stimuli and characterized using the CIE 1931 2° color matching functions (CMFs). However, there is no universally agreed or clear definition of JNCD. Also, such a specification is widely used in various ways based on an assumption that it is applicable regardless of the actual size of the stimuli and CMFs. In this study, an experiment using a constant stimuli method was carried out. The human observers evaluated a series pairs of test and reference stimuli, with a field of view (FOV) of 2° or 10°. The chromaticities of the test stimuli were carefully calibrated using four standard CIE CMFs (i.e., CIE 1931 2°, 1964 10°, 2006 2°, and 10° CMFs). The results suggested that the widely used specification of JNCD seems to be derived based on the one standard deviation ellipses, the use of these four CMFs has little effect on the specification, and the JNCD value for stimuli with an FOV of 10° is 0.0025–0.0027 u′v′ unit depending on the CMFs.