Hue-preserving multiscale retinex for color images

In this paper, we propose a hue-preserving multi-scale retinex (MSR) for color images. In a color image restoration process, MSR is applied to each channel (i.e., red, green and blue) independently. Since MSR is included logarithm operation and local illumination of each channel is estimated independently, the hue of retinex output is different from the original (input) image. Hue preservation is necessary for color image processing. Distortion may occur if hue is not preserved. It is known that two operations, scaling and shifting, are hue-preserving operations in RGB color space. In the proposed method, we approximate the relationship between input pixel value and MSR output pixel value by the hue-preserving transformation form which is a combination of scaling and shifting. The efficiency of the proposed method is shown by using color checker and natural images.