面向监控系统的计算机屏幕图像编码/解码器的研制

在空中交通管制等关键系统中要求7×24 h不停机对系统计算机屏幕进行无损记录,同时记录的存储代价不能过大。针对屏幕图像序列的特点,采用图像差异提取、LZSS压缩Huffman编码等技术,实现了一个性能良好的Codec,其CPU占用率比XviD低50%左右,存储代价低40%左右。     

Modulation and coding for information storage

Many of the types of modulation codes designed for use in storage devices using magnetic recording are discussed. The codes are intended to minimize the negative effects of intersymbol interference. The channel model is first presented. The peak detection systems used in most commercial disk drives are described, as are the run length-limited (d,k) codes they use. Recently introduced recording channel technology based on sampling detection-partial-response (or PRML) is then considered. Several examples are given to illustrate that the introduction of partial response equalization, sampling detection, and digital signal processing has set the stage for the invention and application of advanced modulation and coding techniques in future storage products     

Holographic data storage systems

In this paper, we discuss fundamental issues underlying holographic data storage: grating formation, recording and readout of thick and thin holograms, multiplexing techniques, signal-to-noise ratio considerations, and readout techniques suitable for conventional, phase conjugate, and associative search data retrieval. Next, we consider holographic materials characteristics for digital data storage, followed by a discussion on photorefractive media, fixing techniques, and noise in photovoltaic and other media with a local response. Subsequently, we discuss photopolymer materials, followed by a discussion on system tradeoffs and a section on signal processing and en/decoding techniques, succeeded by a discussion on electronic implementations for control, signal encoding, and recovery. We proceed further by presenting significant demonstrations of digital holographic systems. We close by discussing the outlook for future holographic data storage systems and potential applications for which holographic data storage systems would be particularly suited.     

Digital television

It is now recognized worldwide that all television services, including HDTV, will eventually become digital, but there is wide disagreement about the optimum timing for transforming existing analog systems. A major driving force is the ongoing partial merging of television and digital computers in interactive multimedia services involving digital television and applications in areas like information (news), education, medical, entertainment, etc. A major target is to maximize interoperability of video services at all levels, including various resolutions, different transmission and storage mechanisms, as well as bit rates. This paper provides an overview of the current status in digital television, techniques used, future prospects, and research areas that need to be investigated. The maturity of compression techniques needed for digital video storage and transmission, and the establishment of international standards for digital television representation, like MPEG-2, have greatly contributed in this transformation. Recent developments are mentioned, including the American “Grand Alliance” FCC effort for digital terrestrial HDTV broadcasting, and also other efforts for digital television by cable and DBS. The concept of hierarchical multiresolution coding is also explained, and some of its techniques are briefly described     

On iterative decoding in some existing systems

Iterative decoding is used to achieve backward compatible performance improvement in several existing systems. Concatenated coding and iterative decoding are first set up using composite mappings, so that various applications in digital communication and recording can be described in a concise and uniform manner. An ambiguity zone detection (AZD) based iterative decoder, operating on generalized erasures, is described as an alternative for concatenated systems where turbo decoding cannot be performed. The described iterative decoding techniques are then applied to selected wireless communication and digital recording systems. Simulation results and utilization of decoding gains are discussed     

Digital video recording

Through mutual technology transfer between consumer and professional video recorders, the last 20 years has witnessed a rapid evolution from analog to digital recording. Each new digital videotape recorder (VTR) uses different channel coding. This implies that improving the recording density involves the development of new channel-coding schemes together with evolutionary magnetic tapes and heads. As a result, professional digital VTR's offer the best features for video recording. This paper reviews state-of-the-art magnetic recording devices, signal processing techniques for digital recording. It also describes the specifications for home-use digital recorders for current television systems, and discusses disk recording technology in the future     

Equalization techniques for high-density magnetic recording

The advent of digital computers spurred the development of magnetic tape and disk-drive storage systems capable of storing large amounts of digital information. Since the early development of such systems in the 1950s, we have experienced a phenomenal growth in the use of digital storage systems and an equally large increase in storage capacity and storage density. Over the past four decades, the major factor contributing to the large increases in storage density and capacity has been the continuous technological improvements in the design and development magnetic media and heads. As the storage densities increase, signal processing becomes an important tool in the reconstruction of the digital information in the readback process. We present a tutorial treatment of signal-processing techniques for combating intersymbol interference inherent in high-density digital magnetic recording systems. We focus primarily on magnetic disk systems. We observed that the optimum detector for the ISI-corrupted signal is a maximum-likelihood sequence detector (MLSD) that can be efficiently implemented by means of the Viterbi algorithm     

Effective multi-program broadcasting of prerecorded video using VBR MPEG-2 coding

The tradeoff between picture quality and bandwidth usage is a prominent issue in the world of broadcasting. Since broadcasters are able to transmit multiple streams simultaneously in a channel, they face the challenge of guaranteeing the contracted picture quality required by each of the transmitted video streams while maximizing the number of video streams carried in each channel. We have developed an easy to implement MPEG-2 based multi-program video coding system suitable for digital TV broadcast, video on demand, and high definition TV over broadcast satellite networks with limited bandwidth. Compared to present broadcast systems and for the same level of contracted picture quality, our system greatly increases the number of video streams transmitted in each channel. As a result, either a large number of transponders can be freed to carry real-time broadcasting or the level of picture quality can be significantly increased. By switching from tape storage to video server technology, the need for numerous playback (VTR) systems at the headend is eliminated. In addition, the most of the complete MPEG-2 encoders are replaced by much less complex MPEG-2 transcoders. All this means a much more cost-effective solution for broadcast stations.     

数字图像清晰度

给出了数字图像清晰度的多种表达方式,指出空间分解力反映了数字图像清晰度的实质,应推荐使用;定量分析不同数字图像系统在各个方向上所能达到的图像清晰度理论值的计算方法和实际值的估算方法;为适应我国数字视频技术和产业的蓬勃发展,指出并实验了用数字处理技术,在不增加传输、记录开销条件下,提高重建图像清晰度的途径;设计并用计算机生成了多种数字电视清晰度测试信号和图卡。     

Shedding light on the future of SP for optical recording

Optical recording has lagged behind magnetic recording in two key areas: writable/erasable/rewritable media and density gains from advanced signal processing. While there are some writable optical-disk products available, their writing capability pales in comparison to magnetic recording. A great deal of research and development in writable/erasable/rewritable optical media continues and we address this in the article. Of particular interest is the use of near-field optical approaches to dramatically increase the storage density in both magnetic and optical recording. To a great extent, this article is about the future of signal processing for optical recording, since advanced signal processing has not been applied to any great extent in optical recording. The intention is twofold: (1) to provide a summary of current and existing optical recording technologies, and (2) to encourage and motivate work in advanced signal processing for these and other optical systems. We begin by summarizing the optical recording and readback processes and then describe writable optical channels and the gains associated with using partial-response coding techniques. We then describe nonbinary recording and the potential gains due to signal processing. The digital versatile disc (DVD), multilayer recording, and holographic recording are also discussed     

1.544-Mbits/s Transmission of TV Signals by Interframe Coding System

As a powerful tool for economizing on the digital transmission of videotelephone signals, interframe coding techniques have drawn increasing attention, and various interframe coding schemes have been proposed recently. However, many problems remain to be studied in establishing technical feasibility for these techniques and schemes. This concise paper reports on field trial in which a 1.544-Mbits/s digital transmission of videotelephone signals was conducted over Nippon Telegraph and Telephone Public Corporation's (NTT's) PCM100M digital repeatered line between Tokyo and Yokohama, Japan. The experimental interframe codec is based on the well-understood conditional picture element replenishment algorithm. The object of the field trial was to demonstrate, not the validity of the algorithm itself, but the technical feasibility of the interframe coding system as an entity. Experimental results are satisfactory enough to assure us of the system's practicality in the near future.     

Error-correcting two-dimensional modulation codes

Modulation coding, to limit the number of consecutive zeros in a data stream, is essential in digital magnetic recording/playback systems. Additionally, such systems require error-correction coding to ensure that the decoded output matches the recorder input, even if noise is present. Typically, these two coding steps have been performed independently, although various methods of combining them into one step have recently appeared. Another recent development is two-dimensional modulation codes, which meet runlength constraints using several parallel recording tracks, significantly increasing channel capacity. The article combines these two ideas. Previous techniques (both block and trellis structures) for combining error correction and modulation coding are surveyed, with discussion of their applicability in the two-dimensional case. One approach, based on trellis-coded modulation, is explored in detail, and a class of codes is developed which exploits the increased capacity to achieve good error-correcting ability at the same rate as common non-error-correcting one-dimensional codes     

Quality of band-compressed TV services

Some typical digital high-efficiency coding algorithms applied to the different types of digital transmission systems are discussed, and the resultant picture quality degradation is examined. Techniques for bit-rate reduction, which is fundamental to high-efficiency coding, are described, namely interframe prediction and conditional picture replenishment, hybrid coding using the discrete cosine transform, and vector quantization. Pulse-code-modulation noise, coding distortion, and channel coding error are considered. Subjective and objective methods for evaluating coded pictures are described     

FLC and VLC coding for professional digital HDTV recording — Application to D1-like recorders

Digital recording is a key issue for HDTV studio applications. However, digital baseband recording of HDTV has some drawbacks, for example, high tape consumption and the fact that 1.2 Gbit/s recorders are close to technology limits. Bit-rate reduction techniques allow these difficulties to be overcome. This paper deals with two different approaches for picture coding suitable for professional HDTV recording, with special attention paid to compatibility with existing D1 VCRs (video cassettes recorder). The first approach considers that the behavior of a recorder requires FLC (fixed length code) data as opposed to VLC (variable length code) data, and the second approach supposes that the problems generated by use of VLC data can be overcome with preanalysis and extra error protection strategies. Comparisons of efficiency are presented including multiple copying.     

Digital recording in the professional industry. 1. Recordingtechnology

Describes the use of digital techniques in professional sound recording. It outlines the processes of sampling, quantising and channel coding necessary for converting an analogue signal into a digital format suitable for recording on magnetic tape, as well as the signal reconstruction processes are outlined. Popular stationary and rotary head recording formats are described     

Partial-response coding, maximum-likelihood decoding: capitalizing on the analogy between communication and recording - [History of communications]

Signal processing and coding technology for digital magnetic recording is the core technology of the channel electronics module in a hard disk drive (HDD) that processes signals read from magnetic media. In this historical review I focus on what is now widely known as partial-response, maximum-likelihood (PRML) technology, which takes advantage of the inherent redundancy that exists in signals read out of magnetic media; its theoretical foundation goes back to 1970, and it capitalizes on the analogy between high-speed data transmission and high-density digital recording, and that between a convolutional code and a partial-response signal. The first PRML-based product was introduced by IBM in 1990, and PRML technology soon became the industry standard for all digital magnetic recording products, ranging from computers' HDDs and tape drives to micro hard discs used in PCs, mobile phones, and MP3 players; use of the PRML principle has recently been extended to optical recording products such as CDs and DVDs. Its improved version, called NPML (noise-predictive, maximum-likelihood), and variants have been adopted by the HDD industry since 2000. Today, a large number of communication and information theory researchers are investigating use of advanced techniques such as turbo coding/decoding to further improve the density and reliability of both magnetic and optical recording systems.     

Entropy Coded Differential Pulse-Code Modulation Systems for Television

This concise paper describes experiments with a television source encoder which consists of a differential PCM encoder followed by entropy coding. This encoder converts analog television signals into a digital bit stream for digital transmission or storage. When optimized, this type of system is known to perform very close to the rate distortion bound. The differential PCM encoder has a 16-level quantizer during low entropy areas of the picture (quiet areas) but switches to a 6-level quantizer in high entropy (busy) areas of the picture which tend to fill up the buffer. This strategy avoids buffer overflow and has the desirable property that it produces low noise in quiet areas of the picture and higher noise in busy areas of the picture.     

Photorefractive optics in three-dimensional digital memory

To exceed the capacity limitation of the surface-recording method of current optical data storage, the third dimension is introduced with photorefractive materials. Photorefractive materials are suitable for three-dimensional data storage in conjunction with nonlinear optical systems such as the two-photon absorption process of the material for recording and the confocal laser-scanning system for reading. I will describe the systems and the materials for three-dimensional digital memory with the experimental results for read-only memory with photopolymer, erasable memory with a lithium niobate crystal and rewritable memory with photochromic organic materials. The comparison between photorefractive digital three-dimensional memory with conventional holographic three-dimensional memory and near-field memory is also discussed in terms of dynamic range, noise, recording density, and accessibility