Mosaic image generation device and method

There is provided a mosaic image generation technique that eliminates restriction on a material image corresponding to an object image and improves the visibilities of the mosaic image and the material image. A mosaic image generation device comprises: a dividing unit for dividing an object image, from which a mosaic image is generated, into a plurality of blocks; an object image processing unit for calculating, as a target density value, an average density value of each basic color in each of the blocks divided by the dividing unit; a decision unit for deciding from the plurality of blocks alayout block on which the material image is to be laid out, without being restricted by the image of the layout block; a calculation unit for calculating an average density value of each basic color in the material image; and a color correction unit for performing a color correction on the material image such that the average density value of each basic color in the material image becomes the target density value of each