A system and method for correcting vignetting distortion in an imaging sensor of a multi-camera flat panel X-Ray detector. A scintillator converts X-Ray radiation generated by an X-Ray source into detectable radiation. A displacement unit generates, during a calibration phase, relative displacement between the X-Ray detector and an X-Ray source at a plane parallel to the scintillator. The imaging sensor acquires, during the calibration phase, a first and a second partial images, the first partial image is acquired before the relative displacement is generated, and the second partial image is acquired after the relative displacement is generated. A relative displacement measurement unit measures the relative displacement. Coefficients of a preliminary inverse vignetting function are calculated based on differences between corresponding pixels of the two partial images.