1. A method for reducing spatial noise of images, the method comprising: obtaining a plurality of target pixels of an image frame, wherein each of the target pixels has a pixel value; and for each of the target pixels, performing following steps, the following steps including: building an operating block corresponding to the target pixel wherein the operating block is part of the image frame; operating upon pixel values of the target pixel and a plurality of neighboring pixels in the operating block to obtain a variance corresponding to the operating block; judging whether the target pixel is characteristic according to the variance; and based on the judging indicating that the target pixel is not characteristic, and independently of a pixel value of the target pixel, filtering all the pixels in the operating block to obtain a modulated pixel value if the target pixel is not characteristic and updating the pixel value of the target pixel to the modulated pixel value.