A medical imaging apparatus may include an image processor configured to generate an image based on data acquired by an X-ray detector, wherein the image processor determines a magnitude of a noise signal of a scout image of an object, determines a physical quantity of the object corresponding to the determined magnitude of the noise signal, determines an energy value of a monochromatic image by comparing the determined physical quantity of the object and a preset reference physical quantity, and generates the monochromatic image corresponding to the determined energy value.