The present specification discloses an X-ray system for processing X-ray data to determine an identity of an object under inspection. The X-ray system includes an X-ray source for transmitting X-rays, where the X-rays have a range of energies, through the object, a detector array for detecting the transmitted X-rays, where each detector outputs a signal proportional to an amount of energy deposited at the detector by a detected X-ray, and at least one processor that reconstructs an image from the signal, where each pixel within the image represents an associated mass attenuation coefficient of the object under inspection at a specific point in space and for a specific energy level, fits each of pixel to a function to determine the mass attenuation coefficient of the object under inspection at the point in space； and uses the function to determine the identity of the object under inspection.
