Bell Communications Research Inc, the Livingston, New Jersey research organisation owned by the seven regional telephone companies spun off from AT&T Co claims a significant advance towards the economic delivery into homes of television pictures comparable in quality to 35mm movies. The key is a compression technique that enables the signal for a high definition television raster to be compressed into a single channel of the planned fibre optic Broadband Integrated Services Digital Network, taking up under 120M-bits per second of bandwidth, compared with more 1Gbps required to carry an uncompressed high definition signal. The technique involves splitting the signal for the 1,125 lines per frame into four narrower bands. The lowest frequency band is further compressed by discrete cosine transform, the other three bands are compressed via quantisation, the combination achieving a 10:1 reduction in the bandwidth needed with virtually no reduction in image quality. The lab is also testing high definition television-related services such as medical diagnostic imaging and electronic publishing delivery.
