Abstract: A compression/decompression system for an image data performs a motion compensated prediction and an orthogonal transformation in a time-direction with respect to a plurality of picture planes by combining one pair of an A-frame and a B-frame. The system has a motion estimation element for obtaining a motion vector signal with respect to the A-frame from a first block signal, a motion prediction element for outputting a third block signal obtained by performing a motion compensated prediction with respect to the A-frame on the basis of the motion vector signal, and an orthogonal transformation element for outputting a first and second transformed information obtained by performing an orthogonal transformation in the time-direction with respect to a plurality of picture planes on the basis of the first and third block signals.