1. An image denoising method, comprising the steps of: sequentially selecting a pixel in an image as a current pixel, wherein pixels around the current pixel are defined as neighborhood pixels; dynamically determining a current search block enclosing the current pixel and a strength parameter, and determining a comparison block for each of the pixels in the current search block, wherein the comparison block encloses the each pixel; pre-denoising the comparison blocks for the pixels in the current search block; comparing the pre-denoised comparison blocks for the neighborhood pixels with the pre-denoised comparison block for the current pixel to obtain a similarity between each of the neighborhood pixels and the current pixel in the current search block; determining a weighting for each of the neighborhood pixels related to the current pixel according to the strength parameter, the similarity and a distance between the each neighborhood pixel and the current pixel in the current search block; and weighted averaging each of the neighborhood pixels and the current pixel in the current search block according to the weighting to obtain a reconstruction value of the current pixel, wherein the step of dynamically determining comprises: determining a maximal search block enclosing the current pixel and a comparison block for each of the pixels in the maximal search block, wherein the comparison block encloses the each pixel; calculating the ratios of the edge pixels for the sub-search blocks in the maximal search block; and selecting the sub-search block that has the smallest ratio of the edge pixels as the current search block and determining the strength parameter according to the ratio of the edge pixels of the current search block.