Masahiro Wada

Reversible variable length codes

Proposes some reversible variable length codes (RVLCs) which can be decoded instantaneously both in the forward and backward directions and have high transmission efficiency. These codes can be used, for example, in the backward reconstruction of video signals from the data last received when some signal is lost midway in the transmission. Schemes for a symmetrical RVLC requiring only a single code table and for an asymmetrical RVLC having short average code length are introduced. They compare favorably with other reversible codes such as B2 codes in several aspects. >

Error states and synchronization recovery for variable length codes

An efficient technique for obtaining a variable length code (VLC) resistant to synchronization loss due to channel errors is proposed. Bit errors in the channel lead to incorrect decoding of a VLC and result in error states for continuous codewords. In this paper first a precise value is found for assessing the ability of a VLC to recover synchronization from the error states. Next a new transformation for converting a code into another of the same efficiency (equivalent transformation) is introduced, and several VLCs with an identical efficiency are compared through estimation of synchronization recovery in order to find an error-resistant VLC. Based on the equivalent transformation, an efficient method for finding an error-resistant VLC with high recovery performance from among multiple VLCs is described. >

ATM networking and video-coding techniques for QOS control in B-ISDN

Integration of video services are addressed. The view that various types of end-to-end quality of service (QOS) for video communications, ranging from videophone to high-definition television (HDTV), should be supported to utilize broadband integrated services digital network (B-ISDN) services and video data is expressed. End-to-end QOS is recognized as a function of terminal capability and network performance. The key feature of B-ISDN is that both terminal capability and network performance are selectable and controllable. In order to capture the basic characteristics of end-to-end QOS, it is necessary to conduct experiments using a prototype system. A prototype system comprising an asynchronous transfer mode (ATM) switch and video codecs is presented. The ATM switch is based on distributed-memory-switch architecture and it will provide for nonblocking cell-switching capability with a very low cell-transfer delay. Developed codecs conform to H.261 with an additional function of controlling average coding bit rate. The coding bit rate is chosen as a parameter of terminal capability and the cell-loss ratio is chosen as a parameter of network performance. From experiments using a prototype system, a relationship between coding bit rate and cell-loss ratio is obtained. >

Analysis of optimum-frame-rate in low-bit-rate video coding

We analyze frame rate in low bit rate video coding and show that an optimal frame rate can be theoretically obtained. In order to achieve an optimum balance between coded picture quality and motion smoothness, a frame rate has to be selected which is appropriate to parameters such as coding scheme, property of the video signals and coding bit rate. In this paper, coding distortion measured by mean square error due to quantization is analyzed by modeling video signals, and it is shown that the frame rate can be uniquely optimized. The result of this analysis is compared with the results of computer simulation. In addition, the relation between this analysis and the subjective evaluation is described.

Coding Control Schemes for Store- and-Forward Video Codecs.

Coding control schemes are developed for store-and-forward video codecs which transmit high quality pictures through low bit rate digital lines. Video transmission through easily accessable digital networks, such as ISDN and INMARSAT-A HSD service is in demand. The current transmission rates, however, are around 64 kbit/s, and are not sufficient for real-time transmission of high quality video sequences. The store-and-forward video coding approach solves this problem by using rate conversion at the expense of transmission time. Here, new techniques are required for coding rate and quality control.This paper describes a coding rate control scheme that can be used to improve coding efficiency under variable bit rate conditions. It also describes an adaptive pre-filter that optimizes input picture resolutions as well as an edge-preserving post-filter that reduces block noise for subjective quality improvement. Each scheme is evaluated by computer simulation.