A detection apparatus for detecting photons, such as used in radiographic imaging systems includes a detection unit that generates detection signal pulses having a detection signal pulse height being indicative of the energy of the detected photons, a detection values generation unit that generates energy-resolved detection values depending on the detection signal pulses and a signal pulse generation unit that generates artificial signal pulses having a predefined artificial signal pulse height and a predefined generated rate. The detection values generation unit determines an observed rate of the artificial signal pulses having an artificial signal pulse height being larger than a predefined threshold as observed by the detection values generation unit and determines an offset of the detection signal pulses depending on the determined observed rate. This allows reliably determining the offset of the detection signal pulses, which can be used for correcting the finally generated detection values.