Quality Evaluation of Green Jadeite-jade's Lightness Based on CIE 1976 L~*a~*b~* Uniform Color Space

To evaluate the effect of lightness on color, the correlation of lightness and chroma, lightness and color difference was studied. In the three-dimensional uniform color space CIE 1976 L* a* b*, jadeite jade's chroma is positively correlated with lightness when the lightness of green is relatively low of L*19.52; and there's no one-to-one correlation between lightness and chroma when 19.52L*60, but while L*=37.63 the highest chroma 77.64 is reached; when lightness higher than 60, lightness and chroma are negatively correlated. After the calculation of three color-difference formulae CIE DELAB, DECMC, CIE DE2000, it is proven that DL* is the key factor to DE, followed by DC*, while DH* has nearly no contribution to color difference. It is concluded that emerald green quality evaluation of jadeite jade should be primarily based on lightness which is the most intuitive and consistent with the effect of color perception, and then followed by chroma and hue-angle.