Image enhancement and space-variant color reproduction method for endoscopic images using adaptive sigmoid function

This paper presents an image enhancement and space-variant color reproduction method based on adaptive sigmoid function for endoscopic image. At first, using YC_BC_R conversion matrix, the color image is separated into luminance and chrominance components. The adaptive sigmoid function with two controlling parameters is applied on the uniformly distributed luminance pixels. The space-variant color reproduction generates new chrominance components by transferring and modifying old chrominance based on texture information. Finally, new luminance and chrominance components are converted into RGB color image. The proposed method highlights some of the tissue and vascular characteristics as well as pit patterns in lesion and polyp. The performance of the proposed scheme is compared with other related methods in terms of image quality, focus value, efficiency of color reproduction and statistic of visual representation.