关键词: 图像去噪, 轮廓波变换, 平移不变性, 循环平移, 非下采样

Abstract: The contourlet transform is a new extension of wavelet transform，which provides a flexible multiresolution and multidirectional image representation.It can effectively capture the geometric structure of images.Because of the down sampling operation，contourlet transform is not translation invariant，which will introduces the pseudo-Gibbs phenomenon in the processing of image denoising.The cycle spinning and nonsubsampled are introduced to improve the performance of contourlet transform.The computational complexity，visual quality and dependence of the noise level are discussed based on the comparison between the two modified methods.

Key words: image denoising, contourlet transform, translation invariance, cycle spinning, nonsubsampled