An X-ray apparatus is provided for acquisition of images containing spectral information. An X-ray source and a collimator having multiple slits are operable together with a set of line detectors, the line detectors including linear arrays of photon counting channels. Each of the channels includes a photon conversion channel element which is operable to convert photons to electric pulses. A plurality of pulse counters are operable to count pulses in a plurality of different ranges of pulse strength, where the strength of a pulse depends on the energy of the photon. Further, an arrangement is included for an energy subtracting operation.