Digital Compression Techniques Research Articles

Management of hemorrhage of retro hepatic inferior vena cava injury during piggy-back technique for liver transplantation

Injury to large abdominal vessels is still one of the most terrifying results of trauma or intraoperative faults, as the management of the hemorrhage is hardly difficult due to being torrentially and unaware of the proper reparation. The controversial problem is which technique should be preferred in case of injury to RHIVC and how can it be managed with minimal risk. Over two-year period, we retrospectively analyzed the patients who had undergone adult-to-adult liver transplantation and collected data about the injuries to RHIVC during recipient hepatectomy. All patients were treated with the same surgical technique including digital compression and continuous suturing the tear. Twenty five patients (21 male, 4 female) were detected. The causative factors for end stage liver disease included hepatitis B, hepatitis C with or without hepatocellular carcinoma, autoimmune hepatitis, alcoholic hepatitis, cryptogenic hepatitis, Wilson disease, and nonalcoholic steatohepatitis. Mean diameter of the injury was measured 0.5 cm (range: 0.2-1.6). Only three patients (12%) had more than one injury. Mean amount of blood loss between injury and repair was 130 cc (40-350 cc). There was no operative mortality. Calmness of the operative team followed by the appropriate surgical approach is the key of the success in case of any injury to RHIVC. Digital compression technique can be enough to prevent massive bleeding and repair the injury tract without any vascular exclusion that may result with serious postoperative complications. We proposed this technique because of its ability by most surgeon and easy to perform in a safe way.

Objective quality assessment of MPEG-2 video streams by using CBP neural networks

The increasing use of compression standards in broadcasting digital TV has raised the need for established criteria to measure perceived quality. Novel methods must take into account the specific artifacts introduced by digital compression techniques. This paper presents a methodology using circular backpropagation (CBP) neural networks for the objective quality assessment of motion picture expert group (MPEG) video streams. Objective features are continuously extracted from compressed video streams on a frame-by-frame basis; they feed the CBP network estimating the corresponding perceived quality. The resulting adaptive modeling of subjective perception supports a real-time system for monitoring displayed video quality. The overall system mimics perception but does not require an analytical model of the underlying physical phenomenon. The ability to process compressed video streams represents a crucial advantage over existing approaches, as avoiding the decoding process greatly enhances the system's real-time performance. Experimental evidence confirmed the approach validity. The system was tested on real test videos; they included different contents ranging from fiction to sport. The neural model provided a satisfactory, continuous-time approximation for actual scoring curves, which was validated statistically in terms of confidence analysis. As expected, videos with slow-varying contents such as fiction featured the best performances.

Wireless provision of true VoD services and fast access to Internet

AbstractThe evolution of digital compression techniques has made possible the provision of full‐motion video services through networking infrastructures of sufficient bandwidth. This paper presents a wireless broadband network, which is capable of providing true interactive VoD services (with full VCR functions) and fast access to Internet to a number of simultaneous clients. The network is based on frequency hopping spread spectrum (FHSS) technology operating in the 2.4 GHz frequency band. The paper describes the system architecture and configuration adopted in a real environment trial and elaborates on the provided picture quality in a multi‐client environment. Copyright © 2002 John Wiley & Sons, Ltd.

Objective assessment of MPEG-2 video quality

The increasing use of video compression standards in broadcasting television systems has required, in recent years, the development of video quality measurements that take into account artifacts specifically caused by digital compression techniques. In this paper we present a methodology for the objective quality as- sessment of MPEG video streams by using circular back- propagation feedforward neural networks. Mapping neural networks can render nonlinear relationships between objective features and subjective judgments, thus avoiding any simplifying assumption on the complexity of the model. The neural network processes an in- stantaneous set of input values, and yields an associated estimate of perceived quality. Therefore, the neural-network approach turns objective quality assessment into adaptive modeling of subjective perception. The objective features used for the estimate are chosen according to the assessed relevance to perceived quality and are continuously extracted in real time from compressed video streams. The overall system mimics perception but does not require any ana- lytical model of the underlying physical phenomenon. The capability to process compressed video streams represents an important ad- vantage over existing approaches, like avoiding the stream- decoding process greatly enhances real-time performance. Experi- mental results confirm that the system provides satisfactory, continuous-time approximations for actual scoring curves concern- ing real test videos. © 2002 SPIE and IS&T.

Coded channels. Digital television by satellite

Digital compression techniques will allow satellite TV broadcasting to continue to compete effectively with broadband cable. Instead of transmitting a continuously varying analogue electrical voltage to represent the picture, digital television converts each of the pixels that makes up a TV picture into a coded message. Provided that a receiver can decode the digital message, it can build up a completely new picture, dot by dot, on the screen, with perfect results. As digital compression of television signals becomes the norm, and broadcasters try to squeeze ten or more, services down the same bandwidth that used to carry just one analogue picture, lessons will be learned-about what is acceptable on different types of picture material. Variable rates of compression could perhaps be applied to different scenes in real time, and the channel bandwidth provided for each programme being transmitted over a satellite transponder could be varied dynamically according to the data rate that each scene requires. The author discusses these various aspects of data compression and channel coding.

Video Compression Techniques and Multilevel Approaches

Digital compression techniques are applied to video signals to allow their transmission and distribution through a number of media to the viewer. Systems based on transform techniques have been developed for different applications: from videophone to transmission of TV and HDTV with contribution quality. A brief overview of the basic algorithms adopted for the compression is given: discrete cosine transform (DCT), subband coding, entropy coding, and motion evaluation and compensation. The importance of adopting suitable test material to evaluate the coding systems is discussed. In addition, the article mentions the issues presently debated in standardization groups and international projects: multilevel approaches, to provide various levels of resolution and quality for applications ranging from mobile video to HDTV and the benefits that the adoption of progressive scanning formats could provide in terms of coding efficiency and picture quality

Digital Image Compression Based on Visual Perception and Scene Properties

Digital compression techniques have made impressive progress in recent years. Frequently, a reader of a paper on compression is left with the impression that one is getting something for nothing; however, compression can only be achieved by leaving out unnecessary information about the image. A compression ratio of 20:1 simply means that 95% of the information in the original image has been eliminated. There are only two types of information that can be removed without seeing degradation in image quality: information that can be accurately predicted or information that the human visual system cannot see. This article will discuss present compression techniques in terms of these two factors and show how even further compression can be obtained by developing a complete understanding of scene properties and those of visual perception. From an analysis based on present knowledge of visual perception and scene statistics, compression ratios in excess of 50:1 should be achievable without perceptible degradation.

Waveform preserving encoders for the compression of EEG data

This paper discusses several approaches to the redundancy reduction of clinical electroencephalographic (EEG) data. The encoders presented here are basically of two types. The first type compresses EEG data with very little visual or spectral information present in the original lost in the compression/decompression process. The other type compresses EEG data with some loss of visual reconstruction quality (although still acceptable) but with the advantage of achieving high compression ratios, and providing a convenient and natural way for subsequent automated EEG diagnosis. In deriving redundancy reduction encoders, the efficiency of several digital compression techniques has been compared by encoding EEG data. The general approach adopted, however, is not restricted to this class of data, but can be applied (with minor modifications) to other data of similar characteristics. Dieser Beitrag diskutiert verschiedene Verfahren der Redundanzreduktion von Elektroencephalogrammen (EEG) im klinischen Betrieb. Beschrieben werden zwei prinzipielle Arten von Codierern. Beim ersten Verfahren ist der Informationsverlust infolge der Datenkompression und -dekompression verglichen mit dem Original verhältnismäßig gering. Beim zweiten Verfahren entsteht ein gewisser, wenn auch akzeptabler Informationsverlust bei der visuellen Rekonstruktion. Der Vorteil dabei liegt jedoch darin, daß man eine beträchtliche Datenreduktion erreicht, und daß man darüber hinaus einige Einsicht in den Prozeß der Erzeugung des EEGs und eine daraus ableitbare mögliche automatische Diagnose erhält. Beim Entwurf von Codierern zur Redundanzreduktion wurde die Effizienz verschiedener digitaler Kompressionsverfahren an EEGs praktisch erprobt. Die hier vorgeschlagene allgemeine Vorgehensweise ist jedoch nicht auf diesen einen Datentyp beschränkt, sondern läßt sich - mit kleineren Modifikationen - auch auf andere Daten mit ähnlichen Eigenschaften anwenden. Cet article traite de différentes approches possibles en vue de réduire la redondance de données cliniques électro-encéphalographiques (EEG). Les codeurs présentés ici sont de deux types: Le premier type de codeur comprime les données electro-encéphalographiques de sorte qu'après un codage/décodage, la perte d'information sur la forme et sur le spectre du signal initial soit très faible. L'autre type de codeur, s'il provoque à la reconstruction du signal une perte de qualité visuelle (néanmoins acceptable), il permet cependant d'une part un taux de compression élevé et il fournit d'autre part des renseignements sur le processus electro-encéphalographique et par la même un diagnostic automatique. L'efficacité de plusieurs techniques numériques de compression a été comparée en codant des données électro-encéphalographiques. L'approche générale adoptée ne se restreint pas à cette seule classe de données, mais peut être appliquée (avec des modifications mineures) à d'autres classes de données de caractéristiques similaires.

An Instrument for the Measurement of Auroral Electrons and Protons

An instrument to measure the energy spectrum of auroral electrons and protons has been developed and is operational in orbit aboard ATS-5. It uses cylindrical coordinate electrostatic analyzers for detection of electrons and protons in the range of 50 eV to 50 keV. The analyzers focus these particles onto channel electron multipliers, which are followed by special-purpose amplifier-discriminator electronics. These electronics protect against counting losses due to gain degradation attributable to fatigue and to recovery effects associated with high counting rates. The pulse amplifiers have a dynamic range of 1000:1 and resolve 1-?s pulse pairs. Their fixed dead time (td) permits accurate correction to be made for counting rates exceeding l/td. A fast, ultrastable, programmable high-voltage scan system provides differential voltages between 0 and 6400 V in 62 exponential steps to the analyzer plates for energy selection. A digital servo permits either continuous sequential scanning over the 1000:1 range in energy, or automatic tracking of a spectral peak. Digital compression techniques are used to provide maximum data transfer to the spacecraft telemetry.