1. An image processing apparatus, comprising: a pixel buffer unit, for storing a plurality of first pixels of a previous image and a plurality of second pixels of a current image in a sampling window; a pixel difference calculating unit, for calculating a pixel difference between the first pixel and the second pixel at a position corresponding to the first pixel, and outputting a plurality of pixel differences; a motion level determining unit, for deciding a blending value of a pixel of in the sampling window and determining whether the pixel is a static pixel or a moving pixel according to the pixel difference; a blending value determining unit, coupled to the motion level determining unit, for determining a new blending value when the pixel is a static pixel; and a output unit, coupled to the blending value determining unit, for calculating the current image and the previous image using weighted average according to the blending value so as to generate and output an output image when the pixel is a moving pixel; and calculating the current image and the previous image using weighted average according to the new blending value so as to generate and output the output image when the pixel is a static pixel.