Human color impression model for well-ordered color signal sequence with minimum distance

We examine how a seven-color cyclic sequence affects human color impressions. In order to investigate different effects of two sequences, we consider a hexagonal diagram that is a projection of RGB color space from white to black. The hexagonal diagram is roughly corresponding to the hue circle indicated by both hue and saturation in the HLS system. It is assumed that if: i) the projected route is nearly the minimum; ii) each saturation is large; and iii) neighboring colors are not too close to each other, the projected route area is large. Namely the route area indicates the magnitude of naturalness (as a rainbow feeling) for color sequences. The minimum sequence is similar to the order of rainbow colors. On the other hand, the non-minimum sequence is completely different from the order of rainbow colors. Although seven colors in this study are not distributed as rainbow colors, and the seven-color cyclic sequences are also not continuous sequences with gradation, we can propose a human color impression model using the route area indicated by both hue and saturation. In this model, the subject has natural impressions when the route area is large, but the subject has unnatural impressions when the route area is small.