Peridot’s Yellowish-green Color Appearance Evaluation Based On CIECAM02 Color Model

In this paper, the factors influence on yellowish-green peridot’s color appearance is discussed, by transforming the conditions of surround environment, light illuminance and color temperature. The difference and the pros and cons between this two systems in terms of peridot’s color appearance characterization, and also the distance of peridot’s perceptual color and psychophysical color, are analyzed through compared with the CIE 1976 L*a*b* color parameters(lightness, chroma and hue). And through the visual color matching experiment under standard illuminant D65 and A, peridot’s color constancy is studied to seek the appropriate methods for peridot’s yellowish-green color appearance evaluation, and to provide effective reference for the other green gemstones’ color evaluation.48 natural yellowish-green peridots’ tristimulus values XYZ and CIE 1976 L*a*b* color parameters L*a*b* were measured by color i5 color measurement instrument. And peridots’ color appearance parameters are calculated by CIEC AM02 color model, under different surround environment(Average, Dim and Dark), light color temperature(D65, D50, A) and illumination level of D65.The results show that in the process of transforming the viewing conditions, CIECAM02 color model effectively predict the peridot’s complex color appearance phenomena, as the automatic visual brightness balance, the Hunt effect and the Stevens effect.The results of one-way ANOVA and correlation analysis show that, the influence degree of surround environment is brightness Q(r = 0.943)> saturation s(r =-0.936)> colorfulness M = chroma C(r =-0.752)> lightness J(r = 0.630)> hue angle h(r = 0.390), the influence degree of illumination level is brightness Q(r = 0.738)> colorfulness M(r = 0.520)> saturation s(r =-0.512), and the influence degree of light color temperature is chroma C= colorfulness M(r =-0.497)> saturation s(r =-0.366).The comparison between CIECAM02 model and CIE1976L*a*b* uniform color space indicates: 1.CIECAM02 model predicted values were lower than CIE1976L*a*b* uniform color space(AverageDL=9.42, AverageDC=5.09, AverageDh=1.63). 2. Both have advantages and disadvantages on expressing peridot’s color appearance, but have a similar result aspect of hue, CIECAM02’s effect is better in predicting peridot’s lightness, it’s results are located in medium brightness region, which will help peridot have a better overall color appearance performance, and CIE1976L*a*b* prediction is better in chroma, CIE1976 L*a*b* uniform color space prediction is better, and conducive to the high-chroma color appearance of peridot. 3. Peridot’s psychophysical color and perceptual color are both influenced by surround environment and color temperature of the light source, and the difference between those two also change.According to the analysis of visual color matching experiment results, when the illuminant is transformed from D65 to A, although color shift has been more than three NBS chromatic aberration units, 48 peridots sample still maintaining color constancy.Therefore, when evaluating yellowish-green peridot’ color appearance, surround environment, illumination and color temperature of illuminate need to be fully consider, and recommended CIECAM02 model to predict peridot’s color appearance, because its results is more close to human eye color perception, but compared to gemstones of other color series, peridot’s color evaluation range scale should be properly broadened.