1. An image capture method for an image capture system, comprising: (a) performing a compensation to adjust a total gain of the image capture system to an optimized total gain according to modulation transfer function (MTF) value(s) of image(s), such that the image capture system is operated under the optimized total gain; and (b) capturing subsequent image(s) under the optimized total gain, wherein the step (a) further comprises the steps of: setting different total gains to the image capture system to sense the images; estimating the MTF values corresponding to the images; obtaining a maximum of the MTF values; and setting the total gain corresponding to the maximum MTF value to serve as the optimized total gain.