Color image enhancement by highlight-preserving vector transformation and nonlinear mapping

In this paper, a new light-value approaching method to enhance a color image by excluding the effect of incident illumination is proposed. The method uses the highlight-presenting vector transformation, in which the estimated color of illumination is transformed to the white color of natural daylight while preserving the highlight. In the method, the initial transformation matrix using simple vector rotation is corrected by regression, and the corrected transformation matrix is applied to input color. Then the transformed red, green, and blue values of each pixel are nonlinearly mapped to the 8 bit values to be displayed on a natural color output device. The proposed method can produce the enhanced color image fast and efficiently without any space conversion or noticeable distortion