An image processing method, applicable to a digital image device, includes the following steps. At least one original image of different brightness ranges is captured, and more images of different brightness ranges are generated from the original image by using an image post-processing technique. Based on characteristics of the image of each brightness range, the weights of the image of each brightness range are defined. Then, hierarchical fusion is performed on the images of the different brightness ranges according to weight relations, so as to form a high-dynamic-range image capable of presenting features of each brightness range.