Color image enhancement using single-scale retinex based on an improved image formation model

In this paper, we present an improved image formation model and propose a color image enhancement using single-scale retinex based on the model. In the presented image formation model, an input image is represented as the product of global illumination, local illumination, and reflectance. In the proposed color image enhancement, an input RGB color image is converted into an HSV color image. Under the assumption of white-light illumination, the H and S component images remain as they are and only the V component image is enhanced based on the improved image formation model. In the enhancement of V component image, the global illumination is estimated by applying a linear LPF with wide support region and the local illumination by applying a JND (just noticeable difference)-based nonlinear LPF with narrow support region. The reflectance is estimated by dividing the input V component image by the estimated global and local illuminations. After performing the gamma correction on the three estimated components, the enhanced output V component image is obtained from the product of the three results. Finally an output RGB color image is obtained from the original H and S component images and the output V component image. Experimental results show that the proposed method gives output color images of well-increased global and local contrasts, of no color change, and of nearly halo artifact free so that it yields better performance over the conventional color image enhancement methods.