The CIECAM16-Based Lightness Model Incorporating the Helmholtz–Kohlrausch (H–K) Effect Using Heterochromatic Brightness Matching Data

The heterochromatic brightness matching experiment was conducted by adjusting the luminance of the achromatic color to have the same brightness as the chromatic colors. There were eight different sessions with different background and stimulus luminance levels. Twenty observers participated in each session. Four factors affecting the H–K effect were analyzed: saturation, test color luminance, background luminance, and hue angle. As the saturation of test colors increases, the matched luminance also shows a corresponding increase. The matched luminance ratio decreases as the test color luminance increases. The background luminance does not affect the matched luminance significantly. In the hue effect, there is a slightly stronger H–K effect in only the green region and no effect in another region. A new lightness model based on CIECAM16 is proposed. The proposed model considers the various conditions and can accurately predict the lightness, including the H–K effect.