1. A method for reducing image noise, comprising: performing a high-pass filtering operation on a plurality of pixels of a first image according to a default high-pass filtering mask to obtain a high-pass image; performing a low-pass filtering operation on the pixels of the first image according to a first default filtering mask and a second default filtering mask to respectively obtain a first low-pass image and a second low-pass image, wherein the first default filtering mask is different to the second default filtering mask; performing a difference calculation on the first low-pass image and the second low-pass image to obtain a low-pass difference image; performing a pixel weighting calculation on the pixels according to the high-pass image and the low-pass difference image to obtain a pixel weighting mask corresponding to the first image; and calculating the first image according to the pixel weighting mask and one of the first low-pass image and the second low-pass image to obtain a noise reducing image.