1. A method of generating a radiation image, the method comprising: receiving multi-energy radiation data comprising a plurality of pieces of radiation data indicating an inner portion of a subject with respect to a plurality of radioactive rays in different energy bands, respectively; generating, based on the received multi-energy radiation data, radiation data of a radioactive ray in an energy band that is distinct from the different energy bands; and generating a radiation image of the subject based on the generated radiation data, wherein the energy band that is distinct from the different energy bands is determined based on an entire energy band, the entire energy band being determined by combining the different energy bands of the plurality of radioactive rays, and wherein the energy band that is distinct from the different energy bands exists outside of the entire energy band, and wherein the energy band that is distinct from the different energy bands is determined based on one or more of the different energy bands of the plurality of radioactive rays.