One of the problems in vector quantization (VQ) is its relatively long encoding time especially when an exhaustive search is made for the codevector. This paper presents a hashing-based technique to organize the codebook so that the search time can be significantly reduced. Hashing gives the speed advantages of a direct search, while maintaining a codebook of reasonable size. Experiments show that hashing-based VQ sustained image quality as the encoding time was reduced, while full search VQ suffered greatly. For example, for 2/spl times/2 vectors and with 1024 codebook entries, encoding time was reduced by a factor of 10 without significant loss of image quality.

A syntax-based arithmetic coding (SAC) is introduced for applications in very low bit rate visual telephony. An upper bound of SAC on encoding bit rates for finite homogeneous Markov chains is derived and is the source entropy plus a vanishing term depending only on the actual implementation precision. The SAC video coder is implemented in a layered structure; the states of symbol output of video coder are chosen for an efficient performance.

Some psychovisual properties of the human visual system are discussed and interpreted in a mathematical framework. The formation of perception is described by appropriate minimization problems and the edge information is found to be of primary importance in visual perception. Having introduced the concept of edge strength, it is demonstrated that strong edges are of higher perceptual importance than weaker edges (textures). We have also found that smooth areas of an image influence our perception together with the edge information, and that this influence can be mathematically described via a minimization problem. Based on this study, we have proposed to decompose the image into three components: (i) primary, (ii) smooth, and (iii) texture, which contain, respectively, the strong edges, the background, and the textures. An algorithm is developed to generate the three-component image model, and an example is provided in which the resulting three components demonstrate the specific properties as expected. Finally, it is shown that the primary component provides a superior representation of the strong edge information as compared with the popular Laplacian-Gaussian operator edge extraction scheme.

For past I see ibid., vol.4, no.4, p.405 (1995). The use of the image model of Part I is investigated in the context of image compression. The model decomposes the image into a primary component that contains the strong edge information, a smooth component that represents the background slow-intensity variations, and a texture component that contains the textures. The primary component, which is known to be perceptually important, is encoded separately by encoding the intensity and geometric information of the strong edge brim contours. Two alternatives for coding the smooth and texture components are studied: entropy-coded adaptive DCT and entropy-coded subband coding. It is shown via simulations that the proposed schemes, which can be thought of as a hybrid of waveform coding and feature-based coding techniques, result in both subjective and objective performance improvements over several other image coding schemes and, in particular, over the JPEG continuous-tone image compression standard. These improvements are especially noticeable at low bit rates. Furthermore, it is shown that a perceptual tuning based on the contrast-sensitivity of the human visual system can be used in the DCT-based scheme, which in conjunction with the three-component model, leads to additional subjective performance improvements.

A new scheme, based on the concept of stressed curves, is developed for extracting significant curvature points on a planar curve. The authors show that the problem has an interesting analogy to stable configurations of a mechanical structure. The stressed curve is generated by recursively solving a potential energy minimization problem. The resulting algorithm is rather simple and is local since the iteration for each point of the curve uses at most four of its nearest neighbors. Examples and some of the applications of this new scheme are provided along with a comparison with the curvature primal sketch scheme. The proposed scheme offers efficient and accurate extraction of significant curvature points with a smaller computational complexity.>

A distributed real-time video playback application is presented using an isochronous Ethernet to interconnect video clients to dedicated video servers. Special displaying functions such as seeking, pausing, stepping, and regular/fast playing forward and backward are supported, which are all emulated in the server through control messages received from the clients. The video compression scheme is DCT-based and entropy-coded with adaptivity to the local statistical properties. The important property of the coding system is the constant quality of the decoded frames and is reached by minimizing the average bitrate subject to a constraint on an estimate of the quantization error. This coding scheme also gives rise to a higher PSNR performance as compared with JPEG.

The authors described a three-component image model developed based on psychovisual studies of the human visual system. This image model consists of the primary component which contains the strong edge information of the image, the smooth component which represents the background slow-intensity variations, and the texture component which contains the textures. Using the image model, an adaptive discrete cosine transform (DCT) image coder is developed in order to achieve high subjective performance at low bit rates (>

Combined vector quantization (VQ) and two-dimensional discrete cosine transform (DCT) coding of images is discussed. An algorithm for bit allocation for a composite source is developed. This algorithm is used to vary the bit allocation of the transform encoder based on the VQ outputs. An important feature of the scheme is that the bit allocation map used for the scalar quantization of the 2D DCT coefficients varies according to the VQ output-one bit allocation map per VQ codevector. Thus, the VQ achieves two purposes: (1) it performs bit rate reduction, and (2) its output is used to determine the bit-allocation map for the 2D DCT coding. To exploit the interblock correlation, a two-dimensional interblock noiseless coding is used to encode the VQ outputs. Simulation results indicate that performance improvements over several other image-coding schemes can be obtained. The improvements are more noticeable at lower bit rates.>