1. An image data update apparatus, the apparatus updating image data showing an image including two areas, anti-aliasing being applied to pixels around a boundary between the two areas, the anti-aliasing smoothing change of color on the boundary, the apparatus comprising: an image data storage means for storing first image data showing a first image, part of which includes a first component, which has a first area with a predetermined color, the first area separating from each other the first component and a background area of the first component, wherein the anti-aliasing is applied to a pixel around a boundary between the first component and the first area and to a pixel around a boundary between the first area and the background area; and an image data update means for executing an image data update operation having a first step of generating second image data by changing part corresponding to an area including the first component and the first area in the first image among the first image data stored in the image data storage means while maintaining the anti-aliasing applied to the pixels around the boundary between the first area and the background area.