Exploring the CIEDE2000 thresholds for lightness, chroma, and hue differences in dentistry

To evaluate the perceptibility and acceptability CIEDE2000 (K_L:K_C:K_H) thresholds for lightness, chroma and hue differences in dentistry.

A Python-based program was developed to conduct a psychophysical experiment based on visual assessments of computer-simulated images of human teeth. The experiment was performed on a calibrated display. A 40-observer panel: dentists and laypersons (male and female; n=10), evalu- ated three subsets of simulated human teeth: the lightness subset (%∆L₀₀ ≥ 98 %), the chroma subset (%∆C₀₀ ≥ 98 %) and the hue subset (%∆H₀₀ ≥ 98 %), using ∆E₀₀ ≥ 5 units. A Takagi-Sugeno-Kang Fuzzy Approximation model was used as fitting procedure, and 50:50 % lightness, chroma and hue CIEDE2000 (1:1:1) and CIEDE2000 (2:1:1) perceptibility (PT₀₀) and accept- ability (AT₀₀) thresholds were calculated. Data was statistically analyzed using t-test (p < 0.05).

The 50:50 % PT₀₀ for K_L=1 were ∆L₀₀=1.04, ∆C₀₀=1.58 and ∆E₀₀=1.01; and for K_L=2 were ∆L₀₀=0.51, ∆C₀₀=1.58 and ∆E₀₀=0.71. The 50:50 % AT₀₀ for K_L=1 were ∆L₀₀=2.82, ∆C₀₀=3.04 and ∆E₀₀=2.66; and for K_L=2 were ∆L₀₀=1.40, ∆C₀₀=3.04 and ∆E₀₀=1.78. PT₀₀ and AT₀₀ ∆H₀₀ may be considered no computable. A significant difference was found between CIEDE2000(1:1:1) and CIEDE2000(2:1:1), between lightness and chroma metrics, and between observer groups. No differences for lightness and chroma PT₀₀ were found between male and female groups.

It is important to use PT₀₀ and AT₀₀ for lightness, chroma and hue specific to evaluate perceptual sensitivity for color changes in the tooth color space. AT₀₀ for lightness and chroma are influenced by the observer's experience and gender. Males and laypersons show more tolerance for changes in chroma (∆C₀₀) and in lightness (∆L₀₀).

Hue and chroma mismatch are more difficult to be accepted in dental color space.