Estimation of the Helmholtz–Kohlrausch effect for natural images

The Helmholtz–Kohlrausch (H-K) effect is the phenomenon in which two color stimuli have the same luminance but different chroma in a certain hue, so the perceived brightness induced by the two stimuli are different. In expanding gamut, it is necessary to consider the H-K effect. A quantification of the H-K effect is required in order to evaluate and develop display devices for which the change of perceived brightness of gamut expansion must be considered. For quantification of the H-K effect, prediction equations that can derive the equivalent luminance in a single color image have been proposed in previous studies. However, these equations have not been applied to natural images that are important. Therefore, the purpose of this study is to quantify the H-K effect by deriving calculated values for natural images. For this purpose, first, we conducted the quantification of the H-K effect in natural images by deriving the equivalent luminance as calculated values expanding the three prediction equations proposed in previous studies. Next, we carried out a subjective evaluation experiment by varying image's chroma and luminance. We then verified the effectiveness of the calculated values by comparing them with the result from the experiment.