Scatter compensation is achieved in an X-ray imaging system by providing collimation means in the form of shutters (12) to collimate the primary X-ray beam (1) such that the radiation (8) transmitted through a subject (4) to be imaged is incident substantially centrally on the active part (14) of an image detector (3), so as to define an active border (14b), in respect of which scatter levels can be measured. An electrical signal (104) representative of the scatter level is subtracted from the electrical signal (7) representative of the radiation (8) transmitted through the subject, to obtain a scatter-compensated image signal (106).