According to the module principle of visual information processing,the color constancy under variable illumination is studied and a novel color constancy image enhancement algorithm in two steps under variable illumination is presented.After estimating the color offset of an original image using the pixel near edges, the color offset is corrected with white balance.Then,based on the correlation characteristics of three components in RGB color spaces,the RGB three components of the color image are enhanced at the same proportion by brightness gain curved surface to ensure the hue to be a constance.The experiment on the SFU database indicates that the contrast of the processed image is four times as high as that of the original image,and the brightness change is suitable.The algorithm overcomes the ill-posed problem of traditional color constancy algorithm and can better maintain the color constancy for the images under variable illumination with color offsets or lower illuminating,and can enhance effectively the contrast and brightness.