A low bit rate wavelet-based image coder for transmission over hybrid networks
Yasser F. Syed, K.R. Rao · 1999
To handle the increased demand of personal communications over networks, a low bit rate wavelet based image coder is developed for use in multimedia transmissions. The HC-RIOT (Hbomogenous Cbonnected-Rbegion Ibnterested Obrdered Tbransmission) image coder provides a single coded bitstream that can be decoded at different data rates, which permits transmission over varying bandwidth network connections and is receivable by several different performance levels of decoders. This approach uses a wavelet-based transform combined with a two-stage ZTE/SPIHT entropy coder to create a bitstream with properties of progressive transmission, scalability, and perceptual optimization after a minimum bit rate is reached. A wavelet block chain (WBC) method is used in the initial coding of the low-low (LL) subband to separate and label homogenous regions of the image to the decoder without additional overhead in the bitstream. This information is then used to increase coding efficiency in the modified SPIHT module by the creation of a List of Insignificant Regions (LIR). In addition, perceptual quality of low bit rate images can be enhanced by zeromap filtering and weighting of the wavelet coefficients, which can be targeted down to specific regions of interest. Also the WBC method is shown to possibly assist in a spatio-temporal segmentation and object identification type scheme. The transmission format is initially comprised of a highly compressed base layer, which transmits at a fixed bit rate to provide a minimal quality image, and two enhancement layers, which provide progressive transmission of improvements to the base layer image. This three-layer format is compatible with an unequal channel protection strategy, which is used for error resiliency of transmission through networks. The image coder is designed to operate efficiently from 0.04 bpp to 0.4 bpp (200–20:1 compression ratio), which is suitable for low bit rate transmissions. The overall objective is to develop an image codec for transmission over hybrid networks at low bit rates, which also considers its integration into a video object coder as part of its design.