1. An image enhancement method, comprising the steps of: receiving an image described in first image format; and, for each pixel in the image: determining whether the pixel is on the edge; determining whether the value of the pixel in a second image format falls into the range of skin tones; generating a first smooth filter mask if the pixel is not on the edge and the value does not fall into the range of skin tones; and performing a smooth process on the pixel according to the first smooth filter mask.