The hybrid contextural algorithm for reading real-life documents printed in varying fonts of any size is presented. Text is recognized progressively in three passes. The first pass is used to generate character hypothesis, the second to generate word hypothesis, and the third to verify the word hypothesis. During the first pass, isolated characters are recognized using a dynamic contour warping classifier. Transient statistical information is collected to accelerate the recognition process and to verify hypotheses in later processing. A transient dictionary consisting of high confidence nondictionary words is constructed in this pass. During the second pass, word-level hypotheses are generated using hybrid contextual text processing. Nondictionary words are recognized using a modified Viterbi algorithm, a string matching algorithm utilizing n grams, special handlers for touching characters, and pragmatic handlers for numerals, punctuation, hyphens, apostrophes, and a prefix/suffix handler. This processing usually generates several word hypothesis. During the third pass, word-level verification occurs.>

The multimedia interactive conferencing application (MICA), a personal-workstation application for multipoint visual teleconferencing, is described. MICA allows people at two or more locations to share visual material such as documents, photographs, and computer screens in a highly interactive way. It supports the distribution, storage, retrieval, and high-quality display of visuals, real-time interaction by pointing and annotation, and meeting services facilities. The context of multimedia teleconferencing and computer-supported cooperative work is established, relating earlier research to the design of MICA. The services MICA offers are outlined. The handling, compression, and display of multiple media, and the design of a suitable user interface for MICA are discussed.>

The multipoint communication layer (MCL) is a generic multipoint communication service designed to support highly interactive multimedia conferencing applications. It supports full-duplex multipoint communication between an arbitrary number of connected locations over a variety of networks. MCL design was driven by the demanding real-time multipoint communication requirements of MICA (multimedia interactive conferencing application). The authors establish the context for MCL by considering MICA's communication requirements and reviewing related work in the area of multipoint communication. They present the overall design of the MCL service and describe its communication primitives, protocol message structures, and implementation. Comparison is made with alternative strategies and the use of MCL services for other applications is examined.>

Provides an overview of the technical articles and features presented in this issue.

In this paper several video conferencing systems are discussed. These include single person-camera, voice-switched, split-screen, continuous presence, and virtual space systems. Special emphasis is placed on the more recent video conferencing systems, i.e., the continuous presence and the virtual space systems. The role of digital signal processing in the video conferencing environment is discussed. The interaction between service definition, the video conferencing system, and the digital signal processing requirements is highlighted.

This paper presents the coding algorithms and simulation results of multimode movement-compensated interframe video coders operating at 15 and 20 mbits/s for broadcast applications. The coding algorithms are based on a motion-compensated predictive coding approach. Simulation results using samples of broadcast video sequence indicate that excellent picture quality is obtained at the 20 Mbit/s transmission bit rate. Results of informal subjective evaluation of picture quality are also presented.

This paper describes a technique for varying the quantization characteristics in a Differential Pulse Code Modulation (DPCM) System. A multiplier, based on already transmitted picture elements (pels) which are spatially close to the pel being coded, is used to multiply the prediction error in a DPCM system. This multiplied prediction error is quantized by a fixed quantizer. Coarseness of quantization is thus dependent on the value of the multiplier, which is adjusted on the basis of the sensitivity of the human observers to quantization errors. The implementation is particularly useful in those cases where the quantizer outputs are coded using fixed length code words. Computer simulations on a variety of pictures indicate that a good quality picture can be produced by using a quantizer having between 8 to 10 levels and a two-dimensional predictor. Similar picture quality can be obtained by a simple nonadaptive previous element DPCM system having a quantizer with 13 to 16 levels.

In developing countries telecommunication policies are based on the urban development program. It is pointed out that the telecommunication needs of the developing countries lie in both the urban and rural areas and as a result two distinct networks, urban and rural, are needed. Establishment of a National Rural Telecommunication Agency is suggested to implement the concept of rural networks.