An image processing device to reduce noise in a medical image includes first and second generators, a detector, and a corrector. A first image is generated based on data corresponding to photons with a first energy from among data that is obtained based on an energy of radiation that has passed through a subject and a second image is generated based on data corresponding to photons with a second energy. The detector finds, in the second image, a second block having a similar pattern of pixel values to a first block included in the second image. The corrector reduces noise by correcting pixel values of a third block in the first image corresponding to the first block based on new pixel values of the third block that are calculated by using pixel values included in a fourth block in the first image.
