The invention provides a display unit which can improve emission efficiency of lights for image display, and assure luminance of display images. Developed mass may be increased or decreased by changing set points such as a photoreceptor roll charge, development bias or raster output scanner laser power. The tapes are mounted on a backing block which is rotated to move the tapes from a line contact with the top bevel of the wafer to a line contact with the bottom bevel of the wafer. Thus, the image coding method, image decoding method, image coding apparatus, image decoding apparatus, program, computer data signal, and image transmission system, which are capable of enhancing efficiency of data compression in coded data by reflecting characteristics of image data to be coded on coding conditions, are realized.