1. A method for filtering image noise out, comprising: acquiring a YUV image, and performing image noise filtering process to an unfiltered pixel in a color channel in the image as follows; judging the pixel currently detected in accordance with all the pixels in a preset N*M matrix centering on the pixel currently detected; if the pixel currently detected is in a flat region, performing the following steps: step S 1 , calculating and outputting a filtering strength parameter which is corresponding to the pixel currently detected in accordance with a Y-component of all the pixels in the N*M matrix; step S 2 , filtering the pixel currently detected in accordance with the filtering strength parameter; step S 3 , accomplishing the image noise filtering process performed to the pixel in the color channel; wherein, N≧3, M≧3, and both N and M are odd numbers.