An image processing device that outputs a raster image to an image forming unit that forms an image at a first resolution based on the raster image, generates a raster image at a second resolution that is lower than the first resolution; inspects pixels of the generated raster image having the second resolution, and if there is a pixel group including a pixel and pixels surrounding the pixel that has a layout pattern identical to a predetermined layout pattern, replaces the pixel with a predetermined raster image having the first resolution; inspects pixels of the raster image having the first resolution, and if there is a pixel group including a pixel and pixels surrounding the pixel that satisfies a predetermined condition, replaces the pixel with a pixel of a different color; and outputs the raster image having the first resolution subjected to line-thinning to the image forming unit.