A distortion of image data is corrected by performing a coordinate transformation of the image data by using { X = x + f ⁡ ( x - x 0 , y - y 0 ) Y = y + g ⁡ ( x - x 0 , y - y 0 ) where X and Y represent coordinates of a transformation source which is the image data after the correction of the distortion, x and y represent coordinates of a transformation destination which is the image data having the distortion, x0 and y0 are offset values in x direction and y direction, respectively, and f and g are correction functions.