Image data of first and second planes are created based on display image data containing first and second image data. At least a portion of the first plane corresponding to a display region of the second image data is set to have a color other than black. When the second image data is black, the first image data is set for a first region of the second plane corresponding to a display region of the first image data, and a second region of the second plane corresponding to the non-display region of the first image data is set to a transparent mode. The created image data may be blended so that an image of the image data of the second plane can be superimposed on an image of the image data of the first plane. The blended image data may be used to display an image display panel.