A spherical perceptual color model

Abstract

The paper introduces a transformed spherical model to represent the color space. A circular cone with a spherical top tightly circumscribing the RGB color cube is equipped with a spherical coordinate system. Every point in the color cube is represented by three spherical coordinates, with the radius ρ measuring the distance to the origin, indicating the brightness attribute of the color, the azimuthal angle Θ measuring the angle on the horizontal plane, indicating the hue attribute of the color, and the polar angle θ measuring the opening of the circular cone with the vertical axis as its center, indicating the saturation attribute of the color. Similar to the commonly used perceptual color models including the HSV model, the spherical model specifies color by describing the color attributes recognized by human vision. The conversions between the spherical model and the RGB color model are mathematically simpler than that of the HSV model, and the interpretation of the model is more intuitive too. Most importantly, color changes perceptually smoother in the spherical color model than in the existing perceptual color models.