1. An image processing apparatus for generating an output image having a resolution the same as or higher than that of the original image, the image processing apparatus comprising: first image converting means for converting the resolution of the original image into the same resolution as the output image so as to generate an output resolution image; second image converting means for converting the resolution of the original image into a resolution different from that of the output image so as to generate an intermediate resolution image; similarity information generating means for detecting a plurality of similar areas, in a block in the intermediate resolution image corresponding to a predetermined partial area in the output resolution image, that resemble the partial area, and for generating similarity information including a position of each of the plurality of similar areas in the intermediate resolution image and a weight of the position; texture generating means for generating a texture image by combining high-frequency components of the intermediate resolution image at the position indicated in the similarity information in accordance with the weight indicated in the similarity information; and texture blending means for blending the output resolution image and the texture image so as to generate output image.