High-Speed Transmission of Sequential Freeze-Pictures by Extracting Changed Areas

A very high-speed freeze-picture transmission system via telephone lines is realized by sending only the changed areas from the previous picture. Transmission speed is improved in reverse proportion to the changed areas compared with conventional systems. Increase in circuit size is nominal. The new system is also much simpler than interframe codecs because it does not employ complicated coding mode controls, addressing, or buffering. Block size of the changed areas is selected to satisfy both fast transmission speed and circuit simplicity. High-speed transmission compatible with high picture quality is achieved by extraction of changed blocks using both the average value of the picture signal difference in each block and the maximum value. Protection of picture data against transmission errors is achieved using two synchronizing data groups among tripled addressing data groups. Reduction of impairments due to errors in DPCM picture data using backward decoding is also proposed and adopted.