est neighbor is generally very advances in design and manufacturing technologies will computationally complex, but structured search tech- create hardware devices that will allow greater adapt- niques can provide good bit rates, quality, and compu- ability, interactivity, and interoperability of video appli- tational performance. Tree-structured VQ (TSVQ) [14] cations. For instance, MPEG-7 has defined format free reduces the search complexity from codebook size N to operations for the storage and retrieval of audio-visual log N, with a corresponding loss in average distortion. information that is being used by digital cable TV vendors The simplicity of the VQ decoder (it only requires for "on demand" delivery of digital video content. a simple table lookup for the transmitted codebook index), and its bit rate-distortion performance make it an attractive alternative for specialized applications. The 7.4.3 Video compression complexity of the codebook search generally limits the application requirements use of VQ in real-time applications. VQ quantizers have also been proposed for Interframe, variable bit rate, and A wide variety of digital video applications currently subband video compression methods [5]. exist. They range from simple low resolution and band- Three dimensional wavelet encoding is a topic of width applications (multimedia, PicturePhone) to very recent interest. This video encoding method is based on high resolution and bandwidth (HDTV) demands. This Video compression CHAPTER 7.4 section will present requirements of current and future This represents an increase of approximately 59 times digital video applications and the demands they place on the required NTSC system bandwidth, and about 41 the video compression system. times the full transmission channel bandwidth (6 MHz) To demonstrate the importance of video compression, for current NTSC signals. HDTV picture resolution the transmission of digital video television signals is requires up to three times more raw bandwidth than this presented. The 