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Deriving and dissecting an equally bright reference boundary.

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    This study quantifies the Helmholtz-Kohlrausch effect, the difference between perceived brightness and physical luminance. Findings reveal how saturation and hue influence this perceptual phenomenon, offering insights for color science.

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    Area of Science:

    • Visual Perception
    • Color Science
    • Psychophysics

    Background:

    • The Helmholtz-Kohlrausch effect describes the discrepancy between perceived brightness and physical luminance across different chromaticities.
    • Existing models often struggle to accurately predict perceived brightness due to this effect.
    • Ralph Evans' concepts of brilliance and zero grayness provide a theoretical basis for understanding perceptual brightness.

    Purpose of the Study:

    • To experimentally quantify the Helmholtz-Kohlrausch effect by establishing a perceptual brightness boundary.
    • To investigate the influence of chromaticity, specifically saturation and hue, on the Helmholtz-Kohlrausch effect.
    • To provide a computational framework for brightness modeling and color dimension analysis.

    Main Methods:

    • Experiment 1: Observers adjusted luminance to match a 'glowing threshold' for various chromaticities, incorporating the Helmholtz-Kohlrausch effect.
    • Establishing a reference boundary correlating with MacAdam optimal colors, differentiating surface and illuminant colors.
    • Experiment 2: Saturation scaling across the MacAdam optimal color surface to quantify hue and saturation contributions.

    Main Results:

    • A perceptual brightness boundary was established, serving as a reference for surface and illuminant colors.
    • The Helmholtz-Kohlrausch effect was successfully incorporated by defining equally bright colors at the glowing threshold.
    • Quantified the specific contributions of color saturation and hue to the perceived brightness enhancement.

    Conclusions:

    • The findings provide an ecologically relevant and computationally tractable method for understanding the Helmholtz-Kohlrausch effect.
    • The study offers a refined understanding of color dimensions and their impact on perceived brightness.
    • Implications for advanced brightness modeling, color appearance, and practical applications in displays and lighting are discussed.