An Investigation Into the Bimodal Hue Dependency of the Helmholtz–Kohlrausch Effect

ABSTRACT Recent investigations into the Helmholtz–Kohlrausch (H–K) effect on modern displays have reported a complex, bimodal hue dependency that deviates from classical sinusoidal models. It has been hypothesized that this complexity might be an artifact of CIELAB non‐uniformities rather than a genuine perceptual phenomenon. This study addresses this ambiguity through a comprehensive psychophysical experiment, with results analyzed in parallel using both CIELAB and the more uniform CAM16‐UCS. The analysis reveals that the bimodal signature—characterized by distinct peaks in the cyan–blue and red–magenta regions—persists in CAM16‐UCS, supporting its validity as a perceptual attribute for highly saturated stimuli. Furthermore, it is demonstrated that the eccentricity factor () within CAM16‐UCS inherently captures the primary hue‐dependent trend of the H–K effect. Leveraging this finding, two application‐dependent models are proposed: a hue‐invariant Simplified model suitable for general engineering workflows, and a Fourier model for high‐precision applications requiring characterization of the secondary red–magenta peak. Both models are validated against eight datasets, demonstrating robust performance and offering a practical framework for lightness prediction in modern applications.