Improved HSI color space without gamut problem

While enhancing the intensity or saturation component for high-quality color enhancement, keeping the hue component unchanged is important; thus, perceptual color models such as HSI and HSV were used. Hue-Saturation-Intensity (HSI) is a public color model, and many color applications are commonly based on this model. However, the transformation from the conventional HSI model to RGB model usually generates the gamut problem after processing intensity and saturation in the HSI model. Moreover, the saturation component is always increased or decreased following the change of intensity component no matter what the attainable saturation range is. In this paper, we investigate the relationship between the RGB gamut and the HSI gamut completely. We show that the HSI gamut is larger than the RGB gamut. We make clear that the volume of the HSI color space is 4.5-times of that of the RGB color space. However, the common area of RGB gamut and HSI gamut is large to the middle value of the intensity. Using this property a new HSI model which is called Improved HSI (I-HSI) model is proposed in this paper. We show that the volume of the I-HSI color space is only 1.125-times of that of RGB color space. The gamut problem is almost solved by the I-HSI model.