Data-based modeling of the light source color indicators on the Color Discrimination Index of the Forbidden City typical color paintings.

The Forbidden City, one of the most magnificent palace architectural complexes in the world, has rich color details in the color paintings adorning the beams, plazas, and ceilings of its buildings, which hold high historical and cultural value. How to optimize the light source color indices to improve the color discrimination capability of the Forbidden City typical color paintings in a dim lighting environment is an urgent issue that needs to be addressed. In this study, based on the TM-30-20 standard, we set up 24 lighting conditions with different IES TM-30 fidelity index (Rf), IES TM-30 gamut index (Rg), IES TM-30 hue-angle bin local chroma shift values (Rcs,hj), and correlated color temperature (CCT). Forty-one observers standing at near and far observation distances conducted subjective evaluation experiments on the Color Discrimination Index of three typical Forbidden City architectural color painting samples. The results identified the light source color indices that significantly affect the Color Discrimination Index under different observation distances (near: Rg, Rcs,h7, Rcs,h12, Rcs,h15, CCT; far: Rcs,h12, CCT). The analysis of these indicators' influence on the Color Discrimination Index of the Forbidden City typical color paintings led to the establishment of a corresponding mathematical model. Combined with defined evaluation levels for color discrimination capability, this provides a scientific basis for the evaluation and selection of light sources in the lighting design of the Forbidden City typical color paintings.