A method may include obtaining an initial image that is captured by scanning a scan object using the imaging device. The method may also include performing an iteration process including one or more iterations. Each of the one or more iterations may include determining, according to a thickness model, an equivalent thickness associated with the scan object based on a brightness of a first image and the target brightness, determining one or more second exposure parameters corresponding to the equivalent thickness and the target brightness based on the thickness model, and generating a second image by directing the imaging device to scan the scan object based on the one or more second exposure parameters using the imaging device. The first image may be the initial image in a first iteration of the one or more iterations or an image generated in a previous iteration.