1. An image processing device comprising: an image generator configured to generate a color image including a mark image and a normal image, wherein the image processing device is configured to output the mark image in a semi transparent manner, wherein a contrast of a boundary line of the mark image of a specific color component image of the color image is greater than a contrast of a boundary line of the normal image of the specific color component image of the color image, wherein the boundary line of the normal image is a boundary line distributed within a predetermined distance from the boundary line of the mark image, and the predetermined distance is greater than a half of a smaller one of a horizontal size or a vertical size of a cell at the boundary line of the mark image, wherein the contrast of the boundary line of the normal image is selectively controlled with respect to the specific color component image among a plurality of color component images.