An X-ray imaging system includes an X-ray source, first and second absorption gratings, and an FPD. The first absorption grating passes X-ray emitted from the X-ray source to form a G1 image. The second absorption grating modulates intensity of the G1 image at each of relative positions to form two or more fringe images. The relative positions differ in phase with respect to a period pattern of the G1 image. The FPD detects two or more frames of image data of the fringe images. A defective pixel detector reads two or more frames of image data stored in a memory and obtains a characteristic value of an intensity modulated signal on a pixel-by-pixel basis based on the read image data. The defective pixel detector detects a defective pixel based on the characteristic value obtained.
