Extension of the CCITT visual communication coding algorithm for operation in ATM networks

摘要

This paper describes an adaptation of the Reference Model algorithm, studied in the CCITT—Specialists Group on Coding for Visual Telephony—as future standard for synchronous transmissions, to Asynchronous Transfer Mode (ATM) networks. The adaptation leads to advantages due to the characteristics of an asynchtonous environment, in particular its capability to manage variable bitrate (VBR) flows which permits, for example, to maintain an almost constant image quality over the whole transmission. The new algorithm uses two control parameters—average bitrate and peak bitrate—and permits to improve the overall image quality by means of a powerful resolution control scheme. Experiments have been done in order to know the best trade-off of spatial-temporal resolutions and quantization step that permits to reach a uniform image quality, avoiding critical situations. Some results are presented for conversational and broadcasting image sequences.