1. A digital zooming method, adapted to an image capturing device having a primary lens and a secondary lens, comprising: capturing a scene by using the primary lens and the secondary lens to generate a primary image and a secondary image; performing image rectification on the primary image and the secondary image to generate a primary rectified image and a secondary rectified image; performing feature point detection on the primary rectified image and the secondary rectified image so as to detect overlapping regions respectively in the primary rectified image and the secondary rectified image, and further obtaining a plurality of pixel displacements and a depth map of the overlapping regions respectively in the primary rectified image and the secondary rectified image; when a zooming factor is between 1 and a primary-secondary image factor, performing image zooming and image warping on the primary rectified image and the secondary rectified image to generate a primary warped image and a secondary warped image according to the zooming factor, the pixel displacements, and the depth map, wherein the primary-secondary image factor is a ratio of the secondary rectified image to the primary rectified image; and performing image fusion on overlapping regions respectively in the primary warped image and the secondary warped image to generate a digital zoomed image.