VISUAL DETERMINATION OF HUE SUPRATHRESHOLD COLOR-DIFFERENCE TOLERANCES

This research extends the previous RIT-DuPont research on suprathresho ld color-difference tolerances in which CIELAB was sampled in a balanc ed factorial design to quantify global lack of visual uniformity. The current experiments sampled hue, specifically;, Three complete hue cir cles at two lightnesses (L = 40 and 60) and two chroma levels (C-ab*= 20 and 40) pills thr-ee of the Jive CIE recommended colors (red, green , blue) were scaled visually, for hire discrimination, resulting in 39 color centers. Forty-five observers participated in a forced-choice p erceptibility experiment, where rite total color difference of 393 sam ple pairs were compared with ct near-neutral anchor-pair stimulus of 1 .03 Delta E-ab. A supplemental experiment was performed by 30 additio nal observers in order to validate four of the 39 colar centers. A fet al of 34,626 visual observations were made under the recently establis hed CIE recommended reference conditions defined for the CIE94 color-d ifference equation. The statistical method logit analysis with three-d imensional normit function was used to determine the hue discriminatio n for each color center A three-dimensional analysis was required due to precision limitations of a digital printer used to practice the maj ority of colored samples. There was unwanted variance in lightness and chroma in addition to the required variance in hue, This statistical technique enabled estimates of only hue discrimination. The three-dime nsional analysis was validated in the supplemental experiment, where a utomotive coatings produced with a minimum of unwanted variance yielde d the same visual tolerances when analyzed using one-dimensional probi t analysis. The results indicated that the hue discrimination suprathr esholds of the pooled observers varied with CIELAB here angle position . The suprathreshold also increased with the chroma position of a give n color center; consistent with previous visual results. The results w ere compared with current difference formulas: CMC, BFD, and CIE94. Al l three for-mulas had statistically equivalent performance when used t o predict the visual data. Given the lack of a hue-angle dependent fun ction embedded in CIE94, it is clear from these results that neither C MC nor BFD adequately predict the visual dam. Thus, these and other hu e-suprathreshold data can be used to develop a new color-difference fo rmula with superior performance to current equations. (C) 1998 John Wi ley & Sons, Inc. Col Res AppI, 23, 302-313, 1998.