Comparison of two color-difference formulas using the Bland-Altman approach based on natural tooth color space.

STATEMENT OF PROBLEM: Several formulas to measure color differences have been proposed to improve the correlation between color measurements and visual perception. Despite the progress obtained, equating between formulas is complex, rendering the exchange of information in scientific papers difficult. PURPOSE: The purpose of this study was to determine the relationship between the results provided by classic CIELab (ΔEab∗) and the CIEDE2000 (ΔE00) formulas in the natural tooth color space using the Bland and Altman limits of agreement, to use this relationship to establish the equivalences between the tooth color thresholds of acceptability and perceptibility of both formulas, and to evaluate whether the relationship between ΔEab∗ and ΔE00 is modified depending on the axis on which the changes occur. MATERIAL AND METHODS: The L∗, a∗, and b∗ means coordinates in the 26 shade tabs of the Toothguide 3D Master were used, and color differences were calculated in 325 pairs of shade tabs using the CIELab (ΔE∗ab) and CIEDE2000 (ΔE00) color difference formulas. The results obtained with these formulas were compared, and the limits of agreement after a logarithmic transformation of the data were obtained. RESULTS: The linear relationship between both formulas was ΔE00 =0.66ΔE∗ab. The results obtained with the CIELab formula were between 1.15 (95% confidence interval 1.11 to 1.18) and 2.09 (95% confidence interval 2.03 to 2.15) times higher than those obtained with the CIEDE2000 formula. CONCLUSIONS: In the natural tooth color space, the scale factor between CIEDE2000 and CIELab values changes from 0.46 to 0.90, such that providing an accurate scale factor between both values is difficult. Furthermore, the ΔE00/ΔE∗ab ratio increases with the increase in ΔL∗ and the decrease in Δb∗. The pairs for which the ratio is highest are those in which the difference in color is mainly due to changes in lightness, whereas the pairs for which the ratio is the smallest are those in which the difference in color is mainly due to changes on the blue-yellow axis.

Comparison of the CIELab and CIEDE2000 color difference formulas.

STATEMENT OF PROBLEM: Many color specification systems and color differences have been proposed to improve the correlation between color measurement and visual perception. Although color differences can be quantified using either the CIELab formula (ΔE*(ab)) or the recently introduced CIEDE2000 formula (ΔE00), which captures the perceived color difference better is unknown. PURPOSE: The purpose of this study was to evaluate the CIELab and CIEDE2000 formulas to determine which best reflects the difference in color perception and whether color perception differs by sex. MATERIAL AND METHODS: Forty participants grouped 18 dental resin disks (color range: from 73.6 to 87.5 for L*; from -1.6 to 3.4 for a*; from 18.1 to 36.6 for b*), the only requirement being that each group was formed of disks with chromatically indistinguishable colors. Each participant was free to choose the number and composition of the groups. With the results obtained, a dissimilarity matrix was generated, and nonmetric multidimensional scaling (MDS) was applied to it to obtain the coordinates of the disks within a Euclidean space. RESULTS: The linear correlation coefficient between the interpoint distances of the MDS configuration (MDS_total sample) and the color differences with the CIELab formula (ΔE*(ab)) was 0.176 (P=.029), whereas with the CIEDE2000 formula (ΔE00) it was 0.289 (P<.001). For the configuration obtained in the women's group (MDS_w), the correlation between the interpoint distances and the CIELab color differences was 0.230 (P=.004), and the CIEDE2000 color difference was 0.328 (P<.001). For the configuration obtained in the men's group (MDS_m), the color differences calculated with both formulas reflected the perceived differences more poorly. CONCLUSIONS: Within the limitations of this study, the CIEDE2000 formula reflected the color differences perceived by the human eye better than the CIELab formula (ΔE*ab). In addition, women were confirmed to be more sensitive than men to color differences.