Abstract: Contourlet transform can fast approximate to image signals efficiently, and its ability of image denoising is superior to that of wavelet. In order to retain borders character and texture information well in recovered image, hard threshold approach is often adopted. In this paper, we analyzed three different threshold methods and gave the reason that it is slow to find shrinkage factors. 3σ or 4σ shrinkage factors found through smaller sample images can improve the speed of finding threshold factors and red...