CCC-Trans: Hue-preserving color image enhancement method based on convex combination coefficient transformation

In general, color image enhancement is conducted in a color space represented by hue, saturation, and intensity. It is not always guaranteeing the hue preserving since the color gamut. However, the clipping process could lead to unexpected hue changes if the enhancement process is not guaranteed within a color gamut. In this paper, we propose hue-preserving color image enhancement without the gamut problem based on a transformation of convex combination coefficients. Each pixel is decomposed into a convex combination of white, black, and pure color in the proposed method. The intensity contrast and colorfulness are enhanced while ensuring hue preservation and the color gamut by transforming the coefficients of the convex combination. The novelty of the proposed method is that the coefficients of the convex combination are transformed using histograms derived from a uniform distribution in the sRGB color space. In this paper, we describe the relationship between the coefficients of the convex combination and those of the HSV color space. Experiments show that the proposed method achieves better enhancement results than conventional methods and that the degrees of intensity contrast and colorfulness enhancement can be adjusted. The code is available at https://github.com/uedayos/CCC-Trans . • A color image enhancement model based on the coefficients of convex combinations. • Mathematically describe the detailed properties of the proposed method. • Proposed method expands the possibility of hue-preserving image enhancement method.