A Practical Voiceband Television System Design.

摘要

A need exists to send television on channels of limited bandwidth,particularly 3kHz. Successive images must have adequate picture content yet be frequent enough to give the appearance of motion. A new coding scheme was devised to meet this need for video data compression. A 2400baud system was designed and built. A hierarchy of transmission modes is used which allows the transmitter to choose the most efficient of 3modes to send a line. One mode uses a variable-length Instantaneously Uniquely Decipherable code optimized for the statistics of some typical expected pictures. The picture size is 64by 64elements,each with 4luminance levels. The transmitter has a stored line (129bits) and a two-dimension model to predict the following line. After comparing the prediction to a fresh line the deviations from the prediction are sent. Then the receiver uses the same model to update a similar stored line to be displayed. Frame duration can range from .13to 3.54seconds as determined by the actual picture. (Author)