1. An X-ray apparatus comprising: an image separator configured to separate an X-ray image of an object into material images representing materials in the object; a parameter determiner configured to determine a width of a material of interest (MOI) based on the material images, and determine an enhancement parameter configured to enhance contrast of the MOI according to the width of the MOI; and an image enhancer configured to separate the X-ray image into detailed images respectively including spatial frequencies of different frequency bands, enhance each of the detailed images according to the enhancement parameter, and synthesize the enhanced detailed images to generate an enhanced image.