Study of colorimetrie parameters on normal tongue tip color under different standard illuminants

Objective: Complexional inspection as a traditional method in traditional Chinese medicine (TCM) has been widely used in disease treatment. The work in this paper compare the colorimetric parameters of normal tongue tip color under different illuminants A, B, C, E and D₆₅, and provide experimental basis for the standardization research of the complexional inspection. Methods: In this study, 35 normal undergraduate students were taken as the research subjects. The data of tongue tip color were collected based on the visible reflection spectrum under the revised equal-energy white light (standard illuminant E), and the 380-780nm spectrum curve were obtained. Then the visible reflection spectrum curves under different illuminants were computed based on the spectrum distribution of the standard illuminants A, B, C, E and D₆₅. The CIE XYZ tristimulus values of normal tongue tip color was calculated and the colorimetric parameters on normal tongue tip color under different standard illuminants were obtained and analyzed, such as CIE 1964 chromaticity coordinates, dominant wavelength and RGB values. Results: The results showed that there are significant differences among the visible reflection spectrum curves, CIE 1964 chromaticity coordinates and RGB values under the standard illuminants A, B, C, E and D₆₅. However, with reference to the characteristics of the different standard illuminants, the dominant wavelengths of the normal tongue tip color are consistent. Conclusion: The application of visible reflection spectrum is a standard way to collect colorimetric data for inspection of the complexion.