The invention is an image processing program to generate image data expanded into pixels of an image output device. The image processing procedure includes a procedure to generate second image data expanded into the pixels of the image output device by enlarging first image data expanded into pixels and contained in the rendering record, and a compression procedure that compresses the second image data. Further the generation procedure has an interpolation processing in which, when the difference in the luminance of the image data between adjacent pixels of the first image data is small, the image data of the second image data is rendered to the image data of any of the adjacent pixels, and when the difference is large, the image data of the second image data is rendered to image data that is found from the image data of the adjacent pixels by means of an interpolation calculation.