1. An X-ray imaging system comprising: an X-ray source which emits an X-ray; a first grating having a periodic pattern and disposed in an X-ray propagating path; a second grating which converts the periodic pattern of the first grating into a moire stripe pattern; an X-ray detector including two-dimensionally arrayed transducers which generate an electrical signal corresponding to the incident X-ray emitted from the X-ray source and passing through the first grating and the second grating, the X-ray detector reading the electrical signal generated by the transducers as an image signal to acquire a moire stripe image; a reconstructed image generating member which generates at least one reconstructed image of a differential phase image and a small-angle scattering image of an object based on one or more moire stripe images not including the object and one or more moire stripe images including the object, the moire stripe image not including the object being acquired through irradiation of an object position without the object in the X-ray propagating path with the X-ray from the X-ray source, the moire stripe image including the object being acquired through irradiation of the object at the object position with the X-ray from the X-ray source; a detecting member which detects a salt and pepper noise region in the reconstructed image based on at least one of differential phase noise index, small-angle scattering noise index, phase noise index and visibility noise index calculated by one or more moire stripe images not including the object, and/or one or more moire stripe images including the object; a masked-image generating member which generates a masked image for identifying the detected salt and pepper noise region; and an image processing member which masks or trims at least one of the reconstructed image and the moire stripe images with the generated masked image.