1. An X-ray imaging apparatus comprising: an X-ray source configured to generate and emit X-rays having a preset broadband; an X-ray detector including a plurality of raw pixels configured to detect an average of ten photons or less in response to the X-rays which are emitted and configured to convert the detected photons into an electrical signal; and an image processor configured to produce a plurality of single-energy images, wherein each of the plurality of single-energy images respectively corresponds to a plurality of preset energy bands, by separating the plurality of raw pixels for each of the plurality of preset energy bands based on the electrical signal, and configured to produce a multi-energy image using the plurality of single-energy images.