Tone Correction with Quasi-cubic Splines in a Spherical Color Model

Abstract

In this paper cubic splines are designed as tone correction functions applied to the achromatic component of a spherical color model. Compared with the commonly used color models HSV and HSL, an advantage of the spherical color model is that color changes more perceptually smoothly along its coordinates. However, the spherical color model contains more color points than what can be displayed with the RGB color model, so a tone correction function might cause a gamut issue. The paper demonstrates the gamut issue can be avoided when tone correction functions are well designed and the general tone correction techniques still work well in the spherical color model. A particular type of cubic splines is designed to serve the purpose, and these splines can be adopted by the general tone correction techniques including those for low-key, middle-key and high-key images with correspondingly selected parameters. Experimental results demonstrate that these cubic splines work well for tone correction under the spherical color model.