1. An X-ray imaging apparatus comprising: an image separator configured to extract a first tissue image having a small amount of motion of a tissue, the small amount of motion being smaller than a threshold amount of motion, and to extract a second tissue image with a large amount of motion of a tissue, the large amount of motion being larger than the small amount of motion, from a plurality of image frames; and an image processor configured to correct the second tissue image according to the large amount of motion of the tissue.