Grid foil shadows of a synchronous grid are removable by obtaining an approximate fluoroscopic image by extracting detection signals of pixels not influenced by the grid foil shadows from a fluoroscopic image and carrying out an interpolation process thereon, obtaining a grid foil shadow image by determining a difference between the fluoroscopic image and the approximate fluoroscopic image, obtaining a foil shadow standard image by averaging the grid foil shadow image in a longitudinal direction of the grid foil shadows, and removing the grid foil shadows by determining a difference between the fluoroscopic image and the foil shadow standard image.
