1. An image processing method for improving the definition of an input image, the input image consisting of a plurality of pixels, the pixels being divides into an edge portion and a background portion, the method comprising steps of: (a) generating a noise-eliminated image by subjecting the input image to an open-close and a close-open process; (b) generating an enhanced image by subjecting the input image to a sharpness process; (c) receiving the noise-eliminated image and the enhanced image and determining that each pixel of the input image belongs to the edge portion or the background portion, if one pixel belongs to the edge portion, performing step (d), if one pixel belongs to the background portion, performing step (e); (d) outputting the gray level of the pixel of the enhanced image; and (e) outputting the gray level of the pixel of the noise-eliminated image, wherein the step(c) comprises steps of: (c1) generating a middle image by subtracting the eroded image from the dilated image; (c2) generating a smooth image by subjectinq the middle image to a smooth process; (c3) comparing the gray level of each of the smooth image with a threshold, if the gray level of one pixel is larger than the threshold, performing step (c4), if the gray level of one pixel is smaller than or equal to the threshold, performing step (c5); (c4) determining the pixel belongs to the edge portion; and (c5) determining the pixel belongs to the background portion.