1. A method for image enhancement, adapted to an image processing apparatus, comprising: receiving a low-resolution image; upscaling the low-resolution image so as to generate an upscaled image, wherein the upscaled image comprises a plurality of first pixels; performing edge detection on the upscaled image so as to obtain edge information of each of the first pixels, wherein the edge information of each of the first pixels comprises an edge direction and an edge intensity, each of the edge directions comprises a horizontal component and a vertical component, and a summation of the horizontal component and the vertical component of each of the edge directions is a constant; performing low-pass filtering on the upscaled image by using a low-pass filter so as to generate a low-passed upscaled image, and enhancing an edge region of the low-passed upscaled image according to the horizontal component and the vertical component of each of the edge directions by leveraging a one-dimensional horizontal unsharp masking sharpening method and a one-dimensional vertical unsharp masking sharpening method so as to generate a high-resolution edge image; enhancing a non-edge region of the upscaled image by leveraging a two-dimensional unsharp masking sharpening method so as to generate a high-resolution detail image; and performing image fusion on the high-resolution edge image and the high-resolution detail image according to each of the edge intensities so as to generate a super-resolution image.