1. An image processing apparatus, comprising: a gradient calculation unit configured to perform an operation on an input image to generate gradient magnitudes and gradient angles respectively associated with a plurality of input pixels of the input image; a direction determining unit configured to generate a plurality of interpolation angles and a plurality of directional confidence values according to the gradient magnitudes and the gradient angles associated with the input pixels; a directional interpolation unit configured to perform directional interpolation on the input image according to the interpolation angles, so as to generate a first image with an image resolution different from that of the input image; and a blender unit configured to receive the first image and a second image generated from interpolating the input image, and configured to blend the first image and the second image into an output image according to weights of the first image and the second image associated with the directional confidence values, wherein the resolution of the second image is the same as that of the first image.