1. An image calibration method, for calibrating an image sensed by an image sensor including a pixel array having an effective pixel region and a shading region, wherein the effective pixel region includes at least one target pixel and the shading region includes at least one reference pixel, where each row of the pixel array includes at least one of the target pixel and at least one of the reference pixel, comprising: (a) sensing at least one of the target pixel to generate at least one target pixel value; (b) at a same time point when step (a) is executed, sensing at least one of the reference pixel to generate a calibration value, wherein the reference pixel and the target pixel sensed at the same time point do not belong to the same row, wherein the reference pixel is located in a row N, and the target pixel is located in a row N+X, where X is a non-zero integer having a fixed value and N is a positive integer; and (c) referring to the calibration value to calibrate and output the target pixel value.