1. An X-ray imaging apparatus comprising: an X-ray detector configured to acquire X-ray data by detecting X-rays; and an image processor configured to segment a first image of an object, the first image being generated based on the acquired X-ray data into two or more segmentation regions, to select a region of a second image of a phantom, to identify abnormal materials present in one segmentation region of the two or more segmentation regions based on the selected region, and to generate an image of the object which includes the identified abnormal materials.