The invention relates to a detector unit (100) for the detection of photons of incident radiation. The detector unit (100) comprises a signal processing circuit (40, 50, 60) for generating signals (V0) that are dependent on the energy of a currently detected photon (X) and at least one processing-parameter (Rf). Moreover, it comprises a flux estimator (70) for estimating the flux of photons and for adjusting the processing-parameter (Rf) based on said estimated flux. The flux estimator (70) receives its input (Vi), from which the flux of photons is estimated, from a processing stage that is independent of the output of the signal processing circuit. In a preferred embodiment, the signal processing circuit is or comprises a shaper (40).