A compressive coding device converts three color components of pixel data from the RGB presentation to the YCbCr presentation according to a mapping rule. Converted pixel data are subsequently subjected to irreversible compressive coding, thus producing compressive coded data. Pixel data ascribed to transparency control are converted to a prescribed value out of a mapping range according to the mapping rule. Compressive coded data are supplied to a visual display control device, in which they are decoded and reproduced into original pixel data of the first color presentation. Compressive coded data corresponding to pixel data ascribed to transparency control are rendered with a prescribed color in the RGB presentation which is designated as transparency in advance or not rendered on screen. Thus, it is possible to precisely perform the transparency control without causing a reduction of the compression factor regardless of the irreversible compressive coding and decoding.