Image Contrast Enhancement by Contourlet Transform

We propose a new method for image contrast enhancement, based on a recently introduced 2D directional non-separable transform known as contourlet transform. Conventional 2D wavelet transform is separable and thus can not sparsely represent non-separable structures of the image, such as directional curves. The directionality feature of contourlet transform makes it a good choice for representation of curves and edges in the image. In this paper, a new enhancement function is proposed to enhance the edges by contourlet transform. The method is also compared with two usual contrast enhancement methods, histogram equalization and wavelet based contrast enhancement. It is shown that the contrast enhancement method based on contourlet transform is superior to both histogram equalization and the method based on wavelet transform, in both enhancement of fine structures in the image and denoising