The perception of realism is correlated with the concept of physical gamut

Realism and naturalness remain unresolved questions in vision science. This study investigates whether the physical gamut correlates with realism judgements. We conducted psychophysical experiments where observers judged the realism of natural scenes with target regions manipulated across the CIE 1931 color space. Results initially showed a moderate-to-strong correlation between judgements and a theoretical physical gamut derived from optimal colors. Further analysis revealed that the most detrimental points were in the saturated green region of the CIE 1931 xy chromaticity diagram; removing them yielded a very strong correlation. To explain this discrepancy, we modeled a real-world physical gamut based on USGS and ECOSTRESS spectral libraries. The analysis revealed that the detrimental green chromaticities might be non-existent in the real-world. Since physical gamut theory posits that the visual system constructs internal references through empirical observation of the world, the absence of these colors in nature might be a plausible explanation to the theoretical models failure. Ultimately, the real-world gamut exhibited an even stronger correlation with judgements, supporting our hypothesis while suggesting that the theoretical model may not be the optimal approximation of the actual physical gamut. These findings contribute to discussions on perceptual realism and offer a framework for enhancing rendering technologies.