The invention relates to a pulse shaper (18). The pulse shaper (18) comprises an integrator (19) for generating a pulse having a peak amplitude indicative of the energy of a detected photon, a feedback resistor (22), switchable discharge circuitry (23) for discharging the integrator (19), and a peak detector (24) for detecting the peak of the pulse. The pulse shaper is adapted to start the discharge of the integrator by the switchable discharge circuitry based on the detection of the peak and to connect the feedback resistor in parallel to the integrator during a period of the pulse generation and to disconnect the feedback resistor during another period of the pulse generation. The pulse shaper can be such that the generation of the pulse is substantially unhindered by any noticeable concurrent discharging mechanism while, at the same time, the occurrence of energy pedestals can be efficiently avoided.