An image processing method includes the following steps. An original image is read, and the original image includes a red channel layer, a green channel layer and a blue channel layer. A processing is performed on the red channel layer, the green channel layer and the blue channel layer, respectively, to get a derived red channel layer, a derived green channel layer and a derived blue channel layer. And the derived red channel layer, the derived green channel layer and the derived blue channel layer are combined to form a new image. The processing includes the following steps. Gradient-variations of a plurality of directions of a region are calculated. An average of the gradient-variations is calculated. A calculating procedure is provided to decide diffusion-coefficient equations of the directions, and each of the diffusion-coefficient equations is substituted into an anisotropic diffusion equation.