Abstract: An X-ray imaging device includes a polychromatic X-ray source (10) and a detector (1, 2) having pixels suitable for operating in photon counting mode within at least one energy window bounded by at least one adjustable threshold, and at least one counter so that each pixel delivers an output dependent on the number of photons received by the pixel in the energy windows during a predetermined time interval. This device includes adjustment element (12) capable of adjusting, in real time, the thresholds of the pixels in succession in various energy windows, and processing element (16) for carrying out, in real time, differential processing of the outputs of the pixels in the various energy windows.