A method of processing a signal measured by an energy-resolving detector after passage of radiation through a sample includes receiving a measured count rate for photonic interactions with the detector, fitting a signal model to the detected counts, wherein the signal model is configured to account for a pulse-pile-up effect, the signal model representing a conditional expectation of a frequency of at least uni-directional pulse crossing of at least one energy level, given a physical quantity of a material in the sample, wherein the signal model is expressed in terms of a Fourier representation of a pulse height variable.