Performance evaluation is one of the main research topics in information retrieval. Evaluation metrics are used to quantify various performance aspects of a retrieval method. These metrics assist in identifying the optimum method for a specific retrieval challenge but also to allow its parameters fine-tuning in order to achieve a robust operation for a given set of requirements specification. In this work, we present RETRIEVAL, a Web-based integrated information retrieval performance evaluation platform. It offers a number of metrics that are popular within the scientific community, so as to compose an efficient framework for implementing performance evaluation. We discuss the functionality of RETRIEVAL by citing important aspects such as the data input approaches, the user-level performance metrics parameterization, the evaluation scenarios, the interactive plots, and the performance reports repository that offers both archiving and download functionalities.

Nowadays, the huge non-indexing quantities of image archives (especially document images) require the development of intelligent tools for their retrieval with convenience comparable of the texts search engines. The proposed technique addresses the document retrieval problem by a word matching procedure. It performs matching directly in the images bypassing OCR and using word-images as queries. It is constituted of two different parts: The offline and the online operation. In the offline operation, the archive of document images is examined and the results are stored in a database. The online operation consists of the Web interface, the creation of the word's image and finally, the matching stage. The proposed matching process it can be described shortly as a two-threshold rating system. Finally, the proposed system has been build and it can be found in at the Web address: http://orpheus.ee.duth.gr/irs2.

To efficiently compress rasterized compound documents, an encoder must be content-adaptive. Content adaptivity may be achieved by using a layered approach. In such an approach, a compound image is segmented into layers and then the appropriate encoders are employed to compress these layers individually. A major factor in using these standard encoders efficiently is to match the layer characteristics to these of the encoder by using data filling techniques to fill-in the initially sparse layers. In this work, we propose a sub-optimal non-linear projections scheme that efficiently matches the baseline JPEG coder in compressing background layers, leading to smaller files with better image quality.

By applying the latest technologies in image compression for managing the storage of massive image data within cultural heritage databases and by exploiting the universality of the Internet we are now able not only to effectively digitize, record and preserve, but also to promote the dissemination of cultural heritage. In this work we present an application of the latest image compression standard JPEG2000 in managing and browsing image databases, focusing on the image transmission aspect rather than database management and indexing. We combine the technologies of JPEG2000 image compression with client-server socket connections and client browser plug-in, as to provide with an all-in-one package for remote browsing of JPEG2000 compressed image databases, suitable for the effective dissemination of cultural heritage.

We present the behavior of the JPEG2000 coding scheme over noisy or congested communication channels and highlight the cost analysis aspect. Two error schemes are considered including bit errors and packet dropping effects. Two bit error methods are used, consisting of flipping or dropping the bits, and various packet sizes are put to the test of packet dropping. Extensive performance results are presented and the overall cost analysis is emphasized.

In complex color documents, text, drawings and graphics occur with millions of different colors. In many cases, text regions are overlaid onto drawings or graphics. A new method is proposed for the automatic detection and extraction of text in mixed type color documents. The proposed method is based on a combination of an adaptive color reduction (ACR) technique and a page layout analysis (PLA) approach. The ACR technique is used to obtain the optimal number of colors. Then, the image is split to separable binary images, each one corresponding to every principal color. The PLA technique is applied independently to each one of the color planes and identifies the text regions. A merging procedure is applied in the final stage to merge the text regions derived from the color planes and to produce the final document.

A new alternative is proposed for reducing the power consumption of the portable (battery-powered) units operating in a mobile packet-data network. First, a review of the current power-saving protocols is given. It is shown that the most common means for conserving power is the intermittent operation of the receivers (at the portable units) and a central administration authority that synchronizes the receivers. Some drawbacks of the synchronous operation lead us to the introduction of an asynchronous power-saving protocol, where no central synchronization is necessary and where each terminal may control its power consumption relative to its current needs. According to the proposed power-saving page-and-answer protocol, an acknowledgment paging procedure is preceding every packet transmission in order to alert mobile terminals with pending traffic. Steady-state performance is evaluated with the aid of simulation. The relationship between the achieved power-saving and the mean packet delay degradation is presented. Finally, we express some notable implementation issues and some considerations regarding the employment of this protocol as a supplementary power-saving service in microcellular mobile data networks and wireless local area networks.

Two forms of a sampling theorem for concentric circles are established for a bandlimited two-dimensional (2-D) function. The location of the samples is prescribed either on equidistant circles or on the roots of the Bessel function J0( ). Both methods give comparable results, however, the number of samples required for their numerical evaluation is significantly less for the root-sampling formulation.

A post-processing method suitable for low bit rate spatial domain block-coded images is described. An adaptive filtering process is employed to reduce the visually annoying artefacts introduced from compression. The decision-based filtering uses an estimation of the local characteristics of the coded image. For the areas of low image detail a smoothing operator is used; whereas in the high image detail areas (edges, texture) an adaptive Gaussian-type filter is employed. The main advantage of this filter is that the shape and the position of the Gaussian kernel are adjusted according to the characteristics of the local image region. Simulation results demonstrate that this method enhances the quality of coded edges and reduces annoying blocking effects, resulting in a better picture quality.

Entropy coders, such as Huffman and arithmetic coders, achieve compression by exploiting nonuniformity in the probabilities under which a random variable to be coded takes on its possible values. Practical realizations generally require running adaptive estimates of these probabilities. An analysis of the relationship between estimation quality and the resulting coding efficiency suggests a particular scheme, dubbed scaled-count, for obtaining such estimates. It can optimally balance estimation accuracy against a need for rapid response to changing underlying statistics. When the symbols being coded are from a binary alphabet, simple hardware and software implementations requiring almost no computation are possible. A scaled-count adaptive probability estimator of the type described in this paper is used in the arithmetic coder of the JBIG and JPEG image coding standards.

An image compression algorithm is presented that is suitable for transmitting a high-resolution (400 dot/in) black-and-white (two-tone) facsimile image over a packet network. The algorithm decomposes the image into nondroppable (essential) and droppable (supplementary) bits. The nondroppable bits describe the image at low resolution (200 dot/in) and can be coded with any of the standard CCITT Group 3 or Group 4 techniques. Thus, the algorithm is compatible with the large installed base of Group 3 facsimile machines. The droppable (supplementary) bits are approximately 45% of the total number of bits and can be dropped by the network to relieve congestion. The supplementary bits are encoded with a predictive Huffman method. Resynchronization after missing some of the supplementary information presents no serious difficulties. The algorithm is information preserving, assuming that all droppable bits are available, and its compression efficiency is equal to or better than that of direct two-dimensional Group 3 or 4 CCITT encoding of the high-resolution (400 dot/in) image. Frame memory is not needed.>

A circulating-loop experimental technique to simulate the jitter accumulation of a chain of fiber-optic regenerators is described. This technique allows system designer to establish the jitter accumulation characteristics of systems without the need for many test regenerators. An analytic description of how well the loop technique simulates a china of identical fiber-optic regenerators is presented along with a comparison of calculated and simulated jitter accumulation.>

The new lightwave long-haul transmission systems typically use surface-acoustic-wave (SAW) filters for timing recovery, in place of the phase-locked loops favored in slower systems. We report here analytical studies of jitter phenomena allowed by two kinds of filter ripple. The ripple is capable of causing jitter to accumulate exponentially with the number of regeneratorsNin a repeatered line. Such behavior is well known in the case of phase-locked-loop retiming, where the "jitter peaking" that usually appears in the loop response must be carefully limited to avoid exponential jitter growth. We show that equivalent phenomena can appear when the SAW filters exhibit passband ripple, or, as previously reported in condensed form, When ripple-free filters are detuned by approximately one-half the full 3 dB bandwidth. Furthermore, in the case of ripply filters, exponential jitter accumulation is found to be much more pronounced for random jitter than for systematic jitter. In addition, the alignment jitter within each regenerator can grow exponentially along the chain of regenerators. Neither of these statements is true in the case of the ripple-free filters previously treated in the literature.

Surface-acoustic-wave (SAW) filters have been generally accepted as the best available choice for timing recovery in repeatered transoceanic fiber transmission systems operating in the range of 300 Mbit/s as well as in other digital transmission systems operating from approximately 0.1 to 1 or 2 Gbit/s. The SAW technology is ready and reliable, filter size is consistent with the severe space limitations of undersea repeater housings, and cost is reasonable, especially for the transversal (tapped-delay-line) filter type. This paper updates the relationship between system performance and the characteristics of transversal SAW filters, which have a finite impulse response and non-minimum-phase behavior. New results relate to passband ripple (typical in these filters), thermal characteristics, and the impact of the-delay-line structure on filter "ringing" time.