The invention relates to an X ray pre exposure control device (10) an X ray imaging system (1) an X ray imaging method and a computer program element for controlling such device and a computer readable medium having stored such computer program element. The X ray pre exposure control device (10) comprises a subject detection unit (11) a subject model unit (12) an interface unit (13) a processing unit (14) and a display unit (15). The subject detection unit (11) is configured to detect subject data of the subject (111) to be exposed. The subject model unit (12) is configured to provide a subject model and to refine the subject model based on the subject data into a refined subject model. The interface unit (13) is configured to provide setting data of an X ray unit (131) to be used for exposing the subject. The processing unit (14) is configured to calculate a virtual X ray projection (151) based on the refined subject model and the provided setting data. The display unit (15) is configured to display the virtual X ray projection (151).
