Virtual pixels not included in input image data are arranged before a first input pixel and after a last input pixel of an input pixel array, respectively. A position of a first output pixel is determined so that a difference between a position of the first input pixel and the position of the first output pixel equals a difference between a position of the last input pixel and a position of a last output pixel. Pixel data of an output pixel before the first input pixel is interpolated based on pixel data of the virtual pixel before the first input pixel and pixel data of the first input pixel. Pixel data of an output pixel after the last input pixel is interpolated based on pixel data of the virtual pixel arranged after the last input pixel and pixel data of the last input pixel.