An image processing device in a projection system that includes a first image generation section adapted to project first image on a projection surface and a second image generation section adapted to project second image on the projection surface so as to overlap the first image is disclosed. The image processing device includes: a pixel shift amount calculation section adapted to calculate a pixel shift amount between the first image and the second image; a modulation transfer function (MTF) obtaining section adapted to obtain MTF at a predetermined frequency, corresponding to the pixel shift amount calculated by the pixel shift amount calculation section; a correction filter generation section adapted to generate a correction filter adapted to correct the MTF so that the image displayed on the projection surface has desired sharpness; and a filter applying section adapted to apply the correction filter to image data corresponding to the image.