Abstract: An image data recording and transmission system is described in which a data compressor 76 decorrelates input image data into sub band component data, a data recorder 78 stores the sub band data, a data decompressor 80 decompresses data read from the data recorder and a transmission signal generator 82 produces a bandwidth limited transmission signal from the decompressed data. The combined action of a data sequencer 18, a quantizer 114 and an entropy encoder 20 within the data compressor act to remove from the data stream that information corresponding to frequencies not transmittable with the bandwidth limited transmission signal (e.g. PAL or NTSC) subsequently produced by a transmission signal generator 82. Accordingly, the data recorder need not use storage capacity recording data which cannot be used by the transmission signal generator.

Abstract: A data compression apparatus is described which applies a dynamically variable degree of quantisation Q.sub.s to input data so as to control blocks of output data to have a predetermined maximum size. The dynamic control can be carried out on an inter-block basis or an intra-block basis. An overflow detector is provided for inserting an overflow indicator within blocks of compressed data to indicate when overflow has occurred.