1. A method for calculating a scatter estimate for scatter correction of detection data from a subject in a tomographic scanner, the detection data representing the scattered events and unscattered events of photons emitted in the subject, the method comprising the steps of: determining an estimate of the unscattered events; determining a simulation of the scattered events; determining a value of a scale factor by fitting the sum of the estimate of the unscattered events and a product of the scale factor and the simulation of the scattered events to the detection data ; and determining the scatter estimate as the product of the scale factor having said value and the simulation of the scattered events.