1. A stereoscopic image system, comprising a memory for storing a program; and a processor configured to execute the program to perform the steps of: receiving a two-dimensional image and a corresponding depth image, wherein the corresponding depth image is a gray-level image; generating a depth level map with a predetermined number of depth levels according to the gray-level image, wherein a depth range of each depth level of the depth level map does not overlap with each other; generating a stereoscopic image pair corresponding to the two-dimensional image according to the two-dimensional image and the depth level map; generating a depth level range map by retrieving a portion of the depth levels within a predetermined depth range from the depth level map; and performing a pixel shifting process and an interpolation process to objects that are in the depth levels within the predetermined depth range of the depth level range map in the stereoscopic image pair to generate an output stereoscopic image pair, wherein the processor further calculates a center line of each object in the stereoscopic image pair according to the depth level range map, and performs the pixel shifting process to the stereoscopic image pair to generate the output stereoscopic image according to the center line, wherein the stereoscopic image pair comprises a left eye image and a right eye image and for each object in a set of objects that has a depth that falls within the depth level range map, each respective object undergoes the pixel shifting process such that a right shifting process is performed only to a portion of the object located at a distance of a quarter width from the center line of the object to the left and right in the left eye image, and a left shifting process is performed only to the portion of the object located at the distance of the quarter width from the center line of the object to the left and right in the right eye image.