1. A white-balance method for use in a multi-exposure imaging system having an image capturing unit, the method comprising: utilizing the image capturing unit to simultaneously capture a first image and a second image of a scene with a first exposure value and a second exposure value, respectively, wherein the second exposure value is lower than the first exposure value, and the first exposure value and the second exposure value comprise individual exposure time and exposure gain; performing light source detection on the second image to obtain light source information and a corresponding light source color ratio of the scene; and performing a color gain process on the first image according to the light source color ratio to generate an output image.