1. A method for photon count-loss calibration in a computed-tomography (CT) scanner, comprising: capturing incident X-ray photons via a plurality of energy-discriminating detectors; determining photon counts of the captured incident X-ray photons in a plurality of energy windows at each energy-discriminating detector; and adjusting the determined photon counts in each energy window for each energy-discriminating detector based on a pre-determined photon count-loss look-up table and the determined photon counts.