Virtual communities are discussed as expressions of the modern tension between individuality and community, emphasizing the role that counterculture and its values played in shaping the virtual community project. This article analyzes postings to the WELL conferences and the online groups that served as incubators and testing ground for the term “virtual community,” revealing how this concept was culturally shaped by the countercultural ideals of WELL users and how the tension between individualism and communitarian ideals was dealt with. The overarching conclusion is that virtual communities act both as solvent and glue in modern society, being similar to the “small group” movement.

In ATM networks cell loss or channel errors can cause data to be dropped in the channel. When digital images/video are transmitted over these networks one must be able to reconstruct the missing data so that the impact of the errors is minimized. We overview the problem of using EZW encoders in channels where data-loss is possible. We also describe an error resilience scheme based on unequal error protection and data interleaving that addresses the problem of using rate scalable encoders over ATM networks

Protection of intellectual property is a critical issue in digital multimedia distribution systems. Cryptographic tools are commonly used for secure delivery of content and access keys to consumers via terrestrial, satellite, cable and Internet transmissions. A third requirement is the distribution of the copyright or usage rights associated with the digital content. The integrity, as opposed to security, of this data is essential to prevent unauthorized modification. Two approaches have been proposed in the open literature: allocating special fields in the transport stream and embedding a watermark into multimedia content. We present two new methods, based on secret sharing, to create channels with guaranteed data integrity.

In this paper, ultrasound breast image segmentation is improved by using the volumetric data available in neighboring slices. The new algorithm extends the EM/MPM framework to 3D by including pixels from neighboring frames in the Markov Random Field (MRF) clique. In addition, this paper describes a unique linear cost factor introduced in the optimization loop to compensate for the attenuation common to ultrasound images.

Unlike conventional layered scalable video coding, leaky prediction layered video coding (LPLC) introduces a leaky factor /spl alpha/, which takes on values in the range between 0 and 1, to partially include the enhancement layer in the motion compensation loop, hence obtaining a trade-off between coding efficiency and error resilience performance. In this paper, we use quantization noise modeling to theoretically analyze the rate distortion performance of LPLC. An alternative block diagram of LPLC is first developed, which significantly simplifies the theoretical analysis. Closed form expressions, as a function of the leaky factor, are derived for two scenarios, where drift error occurs in the enhancement layer and no drift occurs within the motion compensation loop. Theoretical results are evaluated with respect to the leaky factor, showing that a leaky factor of 0.4-0.6 is a good choice in terms of the overall rate distortion performance of LPLC.

The globalization of telecommunicative ties between nations is studied from a heterogenization perspective. A theoretical model inspired by Appadurai’s “disjuncture hypothesis,” which stipulates that global flows of communication are multidimensional and reinforce regional/local identities, is tested empirically on an international voice traffic dataset. Spatial-statistical measures (global and local versions of Moran’s I) indicate that countries that share the same linguistic (English, Spanish, or French) or civilizational (Catholic, Protestant, and Buddhist–Hindu) background are more likely to be each other’s “telecommunicative neighbors” and that this tendency has increased over time (1989–1999).

Generally speaking, rate scalable video systems today are evaluated operationally, meaning that the algorithm is implemented and the rate-distortion performance is evaluated for an example set of inputs. However, in these cases it is difficult to separate the artifacts caused by the compression algorithm and data set with general trends associated with scalability. In this paper, we derive and evaluate theoretical rate-distortion performance bounds for both layered and continuously rate scalable video compression algorithms which use a single motion-compensated prediction (MCP) loop. These bounds are derived using rate-distortion theory based on an optimum mean-square error (MSE) quantizer, and are thus applicable to all methods of intraframe encoding which use MSE as a distortion measure. By specifying translatory motion and using an approximation of the predicted error frame power spectral density, it is possible to derive parametric versions of the rate-distortion functions which are based solely on the input power spectral density and the accuracy of the motion-compensated prediction. The theory is applicable to systems which allow prediction drift, such as the data-partitioning and SNR-scalability schemes in MPEG-2, as well as those with zero prediction drift such as fine granularity scalability MPEG-4. For systems which allow prediction drift we show that optimum motion compensation is a sufficient condition for stability of the decoding system.

Real-time multimedia applications over the Internet have posed a lot of challenges due to the lack of quality of service (QoS) guarantees, frequent fluctuations in channel bandwidth, and packet losses. To address these issues, a great deal of research has been done in both video coding and video transmission fields. In this paper we present a logarithm-based TCP-friendly rate control (L-TFRC) mechanism, which can estimate the available bandwidth more accurately and improve the smoothness of the multimedia streaming significantly. We also apply it to a progressive fine granularity scalable (PFGS)-based video streaming. Both simulations and experiments over the Internet confirm the performance of L-TFRC.

Claims about the emergence of a new type of social aggregation—“virtual community”—cover a type of ideological discourse about social interactions. The main cultural resource fueling this ideology is the counterculture and its social project. Virtual community, both as a discursive and as a social practice, is a culmination rather than a resolution of the modern conflict between community and individuality. Presenting virtual community as a panacea for modern social tensions, especially that between individualistic and communitarian ideals, hides from sight not only some of the negative aspects of on-line social life (cliquish behavior and incivility) but also the role played by communication technology in fragmenting modern society.

Wyner-Ziv video coding aims to design encoders based on the Slepian-Wolf and Wyner-Ziv distributed source coding theorems. In this coding scenario, source statistics are exploited at the decoder so that it is feasible to design simplified encoders. The shift of the computational complexity from the encoder to the decoder is suitable for emerging mobile multimedia applications. Many channel coding techniques are used for the construction of distributed video coding systems. In this paper we present a Wyner-Ziv video coding design using low-density parity-check (LDPC) codes. We also present a refined side estimator to further improve the decoded video quality. Experimental results are presented to demonstrate the rate-distortion performance of the method

Printer identification based on a printed document can provide forensic information to protect copyright and verify authenticity. In addition to intrinsic features (intrinsic signatures) of the printer, modulating the printing process to embed specific signatures (extrinsic signatures) will further extend the encoding capacity and utility. One of the key issues with embedding extrinsic signature is the embedded signature should not be detectable by the human observer but is detectable using a matched sensing device and detection algorithm. In this paper, we will investigate the modeling and experimental characterization of the EP process to obtain the modulation threshold such that the embedding signatures are below human visual threshold. An empirical model is established and a heuristic functional inverse is used to obtain the process modulation threshold.

In this paper we present two performance optimization methods for a motion compensated (MC) 2D wavelet video coding technique, which is based on two of the current state-of-the-art codecs: H.26L TML9.4 and JPEG2000 VM7.2. First, a new metric for motion vector selection is proposed to take both edge and texture complexity into account in motion prediction. Second, a frame level rate allocation algorithm, which is an extension of JPEG2000 PCRD (Post Compression Rate Distortion) optimization, is proposed. Experimental results demonstrate the significant performance improvements by these two techniques.

We propose a nested interleaving scheme in order to provide three levels of synchronization in a compressed video bitstream for low data rate wireless applications. The first level of interleaving specifies the starting position of each macroblock (MB) in a video frame. The second level of interleaving provides the start position of each MB header codeword and the start position of each DCT block. The start position of each VLC in a DCT block is located in a known position by the third level of interleaving. Our scheme is assumed to operate in the form of a transcoder, placed before and after the channel, of a MPEG-4 Simple Profile bitstream. Since the three level interleaving provides synchronization on a VLC scale, syntax-based bit error detections can be done in a VLC unit. The detected errors can be repaired syntactically so that the transcoder generates a MPEG-4 compliant bitstream which can then be decoded with a standard MPEG-4 decoder such as MoMuSys (FDIS V1.0).

We discuss in this paper the issues related to image watermarking benchmarking and scenarios based on digital rights management requirements. We show that improvements are needed in image quality evaluation, specially related to image geometrical deformation assessments, in risk evaluation related to specific delivery scenarios and in multidimensional criteria evaluation. Efficient benchmarking is still an open issue and we suggest the use of open-source Web-based evaluation systems for the collective progresses in this domain.