1. An image forming apparatus comprising: an illumination system which sequentially emits illuminating light beams from multiple different irradiation directions with respect to an object and irradiates the object with the illuminating light beams; an image sensor which is arranged at a position where the illuminating light beams that have been transmitted through the object are incident and which captures a plurality of different images in the multiple different irradiation directions, respectively; an image processing section which forms a high-resolution image of the object, having a higher resolution than any of the plurality of images, based on the plurality of images; and a memory which stores data about the ratio of light rays that have been incident on a photoelectric conversion section of each pixel of the image sensor to light rays that have passed through the upper surface of a plurality of subpixels included in the pixel with respect to each of the multiple irradiation directions, wherein the image processing section forms the high-resolution image of the object based on the data that has been retrieved from the memory by extracting, as a vector, a set of pixel values associated with the multiple irradiation directions from pixel values that form each of the plurality of images.