Abstract: An image data coding system comprises a screen-area determining means for determining the area of a screen reproduced on the basis of an input image data; a code-amount assigning control means for controlling regions to which data on the screen are to be assigned and the code amount assigned to each of the regions, on the basis of the results determined on the area of the reproduced screen; and a coding means for coding the image data signal inputted in accordance with the code amount assigned to each of the regions. In an image data coding and/or decoding system, a coding system performs the two-dimensional orthogonal transform of picture signals of all the pixels with respect to inside blocks and of only picture signals of pixels contained in a content with respect to edge blocks, in accordance with a map signal indicative of the position and shape of the content, and it codes the map signal.