- Panasonic-plasma Panasonic's monthly plasma panel production capacity has reached 150,000 units, and plasma will be the dominant product in the market in the future, so Panasonic will bet on plasma TV manufacturing
Performance: In terms of home theater effect, the effect of equilibrium TVs is stronger than that of LCD TVs. Our video expert, senior editor David Katzmaier, explains that this is because LCD TVs typically can't display the kind of blackness that plasma TVs can. So LCD TVs have trouble displaying more detail, and video gamers may feel that the image doesn't have the same "three-dimensional" quality.
While the image quality of LCD and plasma TVs in general has improved from year to year, performance varies widely from manufacturer to manufacturer. Check out CNET's reviews at wvtews.cnet.com before you buy. The reviews in our magazine are picky about performance (it's what we do), so pay attention if you're looking to add a home theater. But if you're just buying a small-screen LCD TV (under 26 inches) for your kitchen or bedroom, don't be too hard on yourself.
Lifespan: LCD TVs have a distinct advantage over plasma TVs in this regard. While the lifespan of plasma TVs varies, it takes about 20,000 hours to reduce to half brightness, while LCDs can go 50,000 hours before reducing to half brightness.
Burn-in and elevation issues: "Burn-in" is a problem with plasma TVs, where a static image remains on the screen for an extended period of time, leaving a "ghost image" of that image on the screen. If a stock ticker or news ticker is displayed below the TV for an extended period of time, or if you frequently watch standard format TV programs on a wide screen, shadows will appear above, below, or on both sides of the screen on the side of the image. While manufacturers take every means to try to solve this problem, it's best to take care of it in your own use, such as not playing still images on the screen for long periods of time and setting the contrast ratio to less than 50 percent.
LCD TVs don't have the problem of burned-in screens and don't have problems at high altitudes, whereas the difference in air pressure at different altitudes can cause plasma TVs to emit an unpleasant humming sound. While some manufacturers have specialized models that supposedly don't have this problem, we still don't recommend plasma TVs if you live at high altitude.
High-definition: most plasma and LCD TVs can display high-definition signals. But beware: To enjoy a truly full HDTV, the display resolution must be at least 1280 x 720. Very few 42-inchers can achieve this resolution, and most 50-inch plasma TVs and almost all LCD TVs larger than 26 inches have no problem. Of course, a less-than-42-inch TV up against a true high-definition TV generally won't notice much difference between the two unless you sit in front of the screen and look closely. For example, while Panasonic's TH-42PA20U model 42-inch plasma TV offers only up to Enhanced Definition resolution (EDTV, 852×480), reception of HDTV on it is still very good, and given the price factor (which can be as low as $3,389 a pop online), it's probably the best 42-inch plasma TV for the money.
Computers and video games: Most plasma and LCD TVs can be used as computer monitors, and many even offer DVI ports for better display performance. Both types of TVs have no problem hooking up a game console. So which is better for gaming? It's hard to make a verdict on the two technologies based on performance alone, but LCD TVs are a safer bet considering that plasma TVs have the potential for screen burn-in.
Digital television: digital television is that all aspects of the studio to launch, transmission, reception are using digital television signals or to the system all signal propagation is through the 0, 1 digital string of digital streams composed of the spread of digital signals, the propagation rate of the digital signal is 19.39 megabytes per second, so the transmission of data streams to ensure that the digital television of the high-definition to overcome the inherent shortcomings of the analog television. The inherent shortcomings of analog television. At the same time also due to the digital TV can allow the simultaneous existence of several standard signals, each digital channel can be divided into several sub-channels, so that both a large data stream - 19.39 megabytes per second, but also can be divided into several sub-streams, such as four, each of which is the rate of 4.85 megabytes per second, which, although the clarity of the image to be greatly reduced, can greatly increase the type of information to meet the different needs. For example, in the broadcast of a sports game, the audience needs high-definition images, the television station should be used 19.39 megabytes per second transmission; and in the news broadcast, the audience's attention is the content of the news rather than the announcer's image, so there is no need to use so high clarity, then only need to be 3 megabytes per second speed can be, the remaining 16.39 megabytes available to the transmission of other content.
Nowadays, digital TV is one of the most talked about and lively topics. Because digital TV is a new thing, some related reports and articles in the introduction of specious concepts, such as "digital TV", "all-digital TV", "all-media TV "digital TV", "all-digital TV", "all-media TV", "multimedia TV" and so on, resulting in confusion and bewilderment of the public. In fact, the meaning of "digital TV" does not refer to our average person in the home of the television set, but refers to the television signal processing, transmission, transmission and reception process using digital signals in the television system or television equipment. The specific transmission process is: the image and sound signals sent by the television station, digital compression and digital modulation, the formation of digital television signals, through the satellite, terrestrial wireless broadcasting or cable transmission, etc., received by the digital television, through the digital demodulation and digital audio-visual decoding process to restore the original image and accompanying sound. Because the whole process is processed using digital technology, therefore, the signal loss is small, the reception effect is good.
The basic principle of digital television
The television video and audio signals digitized, the amount of data is very large, very detrimental to the transmission, so the data compression technology has become the key. There are two ways to realize the data compression technology: one is in the source coding process for compression, IEEE's MPEG expert group has been developed to formulate the ISO/IEC13818 (MPEG-2) international standards, MPEG-2 using a combination of different layers and levels to meet the quality from the family quality to the quality of broadcasting as well as will be broadcasting the quality of high-definition television different requirements, the application of its very broad MPEG-2 has a wide range of applications, it supports standard resolution 16:9 widescreen and high-definition television and other formats, from entering the home of the DVD to satellite television, broadcast television microwave transmission have adopted this standard. The second is to improve the channel coding, the development of new digital modulation technology to improve the unit bandwidth data transmission rate. For example, in the European DVB digital TV system, digital satellite TV system (DVB-S) using orthogonal phase-shift keying modulation (OPSK); digital cable TV system (DVB-C) using orthogonal amplitude modulation (QAM); digital terrestrial open-circuit TV system (DVB-T) using more complex coded orthogonal frequency-division multiplexing modulation (COFDM).
Digital television classification
Digital television can be categorized in the following ways:
(1) According to the classification of signal transmission: can be divided into terrestrial wireless transmission (terrestrial digital television), satellite transmission (satellite digital television), cable transmission (cable digital television) three categories.
(2) Classification by product type: it can be divided into digital TV monitors, digital TV set-top boxes, integrated digital TV receivers.
(3)Classification by clarity: it can be divided into low definition digital TV (image horizontal clarity greater than 250 lines), standard definition digital TV (image horizontal clarity greater than 500 lines), high definition digital TV (image horizontal clarity greater than 800 lines, i.e., HDTV).
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(14)(15)(16) The image format of VCD belongs to the level of low definition digital television (LDTV), and the image format of DVD belongs to the level of standard definition digital television (SDTV).(4) according to the display screen format classification: can be divided into 4:3 format ratio and 16:9 format ratio of two types.
(5) according to the number of scanning lines (display format) classification: can be divided into HDTV scanning lines (more than 1000 lines) and SDTV scanning lines (600 to 800 lines) and so on.
The advantages of digital TV
Digital TV technology has the following advantages over the original analog TV technology:
(l) The signal clutter ratio is independent of the number of consecutive processing. Television signals are digitized with a number of binary two levels to represent, and thus in the continuous processing or in the transmission process after the introduction of clutter, the clutter amplitude as long as it does not exceed a certain rated level, through the digital signal regeneration, may be able to remove it, even if a clutter level exceeds the rated value, resulting in a miscode, you can use error correction coding and decoding technology to correct them. Therefore, in the digital signal transmission process, will not reduce the signal-to-noise ratio. The analog signal processing and transmission, each time may introduce new noise, in order to ensure that the final output has sufficient signal to noise ratio, it is necessary to put forward a variety of processing equipment for a higher signal to noise ratio requirements. Analog signals require S/N>40dB, while digital signals only require S/N>20dB. analog signals in the transmission process noise gradually accumulated, while digital signals in the transmission process, basically does not produce new noise, that is, the signal to noise ratio is basically unchanged.
(2) The effect of nonlinear distortion of the system can be avoided. In contrast, in analog systems, nonlinear distortion can cause significant damage to the image.
(3) The output signal of digital devices is stable and reliable. Because the digital signal is only "0", "l" two levels, "l" level amplitude size as long as to meet the processing circuit may be recognized as "l" level can be, a little bigger, a little smaller does not matter.
(4) easy to realize the signal storage, and storage time and signal characteristics are irrelevant. In recent years, the development of large-scale integrated circuits (semiconductor memory), you can store more than one frame of the TV signal, thus completing the analog technology is not possible to achieve the processing function. For example, the frame memory can be used to achieve frame synchronization and standard conversion processing, to obtain a variety of new television image effects.
(5) due to the use of digital technology, with the computer can realize the automatic control and adjustment of equipment.
(6) digital technology can realize the time division multiplex, make full use of the channel capacity, the use of digital television signals in the line, field fading time, can realize the text multiplex broadcasting (Teletext).
(7) compressed digital TV signal after digital modulation, can be open-circuit broadcasting, in the design of the service area (terrestrial broadcasting), the audience will be a great probability of realizing the "error-free reception" (send "0" to receive "0", send "l" to receive "l"), to receive and see the TV image and sound quality is very close to the studio quality.
(8) can reasonably utilize various types of spectrum resources. In terms of terrestrial broadcasting, digital television can be enabled to analog television quot;disable the channel" (taboo channel), and in the future to be able to use the "single frequency network" (single frequency network) technology, such as l sets of television programs only occupy the same 1 digital television channels and coverage of the whole country. In addition, the existing 6MHz analog TV channels can be used to transmit l digital high-definition TV programs or 4-6 digital regular TV programs of higher quality, or 16-24 digital TV programs of comparable quality to home VHS recorders.
(9) In the synchronous transfer mode (STM) of the communication network, a variety of services can be realized "dynamic combination" (dynamic combination). For example, in digital high-definition television programs, there are often moments when the image details are less. At this time, because of the compressed image data is small, it can be inserted into other services (such as TV program guide, fax, video game software, etc.), without having to insert a large number of meaningless "filler bits".
(10) Encryption/decryption and scrambling/descrambling techniques can be easily implemented for professional applications (including military) as well as broadcasting applications (especially for various types of fee-based services).
(ll) It is scalable, hierarchical, and interoperable, and is easy to transmit over various types of communication channels, especially Asynchronous Transfer Mode (ATM) networks, and is also easy to interconnect with computer networks.
(12) It can be "integrated" with computers to form a class of multimedia computer systems, which will become an important part of the future "National Information Infrastructure" (NII).
Digital television related technology
(1) digital television broadcasting process and means of realization
Digital television broadcasting, the signal process including production (editing), signal processing, broadcasting (transmission) and receiving (display) several processes.
Currently used for digital program production means are: digital video cameras and digital photo cameras, computers, digital editing machines, digital subtitle machines; for digital signal processing means are: digital signal processing technology (DSP), compression, decompression, scaling and other technologies; for the means of transmission are: terrestrial broadcasting transmission, cable (or fiber-optic cable) transmission, satellite broadcasting (DSS) and the broadband integrated service network (DSS). Broadband Integrated Services Network (ISDN), DVD, etc.; used to receive the means of display: cathode ray tube displays (CRT), liquid crystal displays, plasma displays, projection displays (including front projection, rear projection) and so on.
The main function of video coding technology is to complete the compression of the image, so that the signal transmission of digital television from 995Mbit / s reduced to 20 ~ 30Mbit / s. Video coding calculations are mainly based on the following objective: (1) image time correlation. The video signal consists of continuous images, neighboring images have a lot of correlation, to find these correlations can reduce the amount of information. (2) image space correlation. For example, if there is a large block of a single color in the image, then it is not necessary to store all the pixels. (3) Visual properties of the human eye. The human eye on the original image of the distortion sensitivity of different places, the insensitive and irrelevant information to give a larger distortion, even if all of this information is lost, the human eye may not be aware of; on the contrary, the human eye is more sensitive to the information, as far as possible to reduce its distortion. (4) Statistical properties between events. The smaller the probability of occurrence of the event, the greater its entropy value, indicating that the greater the amount of information, the need to allocate a longer code word; conversely, the greater the probability of occurrence, the smaller its entropy value, only need to allocate a shorter code word.
Same as video codec, the main function of audio codec is to complete the compression of sound information. After the digitization of the sound signal, the amount of information is much larger than the analog transmission state, and thus the sound of digital TV can not be transmitted directly as the sound of analog TV, but more than one compression coding process.
The compression coding of audio signals mainly utilizes the auditory properties of the human ear. (1) Auditory masking effect. In human hearing, the existence of a sound masks the existence of another sound, masking effect is a more complex psychological and physiological phenomena, including the human ear frequency domain masking effect and time domain masking effect. (2) Directional properties of the human ear to sound. For high-frequency sound signals above 2KHZ, it is difficult for the human ear to determine its directionality, and thus the high-frequency part of the stereo broadcast does not have to repeat the storage.
The international digital image encoding has developed three standards, H.261, which is mainly used for videoconferencing, JPMG, which is mainly used for still images, and MPEG, which is mainly used for continuous images.
In terms of HDTV video compression codec standards, the United States, Europe, and Japan have differences, and have adopted the MPEG-2 standard. MPEG (Moving Picture Expert Group) means "Moving Picture Experts Group", compressed information can be processed by computers, but also in the existing and future distribution of television broadcast channels.
In terms of audio coding, Europe and Japan have adopted the MPEG-2 standard; the United States has adopted Dolby's AC-3 program, with MPEG-2 as the backup program.
For our country, the future source codec standard will also be the same as the United States, Europe, Japan, the same MPEG-2 standard.
(3) Digital TV multiplexing system
Digital TV multiplexing system is one of the key parts of HDTV. From the sending end of the flow of information, it will be video, audio, auxiliary data and other encoders to send the data bit stream, processed and compounded into a single serial bit stream, sent to the channel coding and modulation. The receiving end is the opposite of this process.
Multiplexers do not exist in analog TV systems. In digital TV, the multiplexer takes the code streams of audio, video, and ancillary data and packages them through a packer (which is the common term for what is actually a data packet) and then compounds them into a single path. Currently network communications data are packaged and transmitted in a certain format. the packaging of HDTV data will give it a basis for scalability, hierarchy, and interactivity.
Pay TV is a direction of TV development now and in the future. The multiplexer can scramble the packaged program information to randomize it, and the receiver has a key to unscramble it.
In terms of HDTV multiplexing transmission standards, the United States, Europe, Japan, there is no disagreement, have adopted the MPEG-2 standard. The U.S. has a dedicated chip for MPEG-2 demultiplexing. I am afraid that our country will also adopt MPEG-2 as the standard for multiplexing transmission.
The HDTV packet length is 188 bytes, which is an integer multiple of the ATM signal element. In the future, optical fiber as the transmission medium, ATM as the information transmission mode of broadband integrated business digital network is likely to become the future "information superhighway" of the main facilities. Four ATM channels can be used to completely transmit an HDTV packet, thus providing a convenient interface between HDTV and ATM.
(4) Digital TV channel codec and modulation demodulation
The purpose of digital TV channel codec and modulation demodulation is to improve the signal's interference immunity through error correction coding, grid coding, equalization and other technologies, through the modulation of the transmission signal on the carrier or pulse string, ready for launch. We are currently talking about the system of digital television in various countries, the standard can not be unified, mainly refers to the differences between countries in that area, specifically including error correction, equalization and other technologies, the difference in bandwidth, especially the modulation method.
The common modulation methods for digital transmission are:
Quadrature amplitude modulation (QAM): high modulation efficiency, requires a high signal-to-noise ratio of the transmission path, suitable for cable television cable transmission.
Keyed Phase Shift Modulation (QPSK): high modulation efficiency, requires a low signal-to-noise ratio in the transmission path, suitable for satellite broadcasting.
Residual sideband modulation (VSB): good resistance to multipath propagation effects (i.e., elimination of ghosting effect is good), suitable for terrestrial broadcasting.
Coded Orthogonal Frequency Division Modulation (COFDM): good resistance to multipath propagation effects and cochannel interference, suitable for terrestrial broadcasting and cochannel network broadcasting.
The U.S. terrestrial television broadcasting so far still accounts for more than half of its television business, so the United States in the development of high-definition television first considered how to disseminate through the terrestrial broadcasting network, and put forward a standard based on digital high-definition television - ATSC. the U.S. HDTV terrestrial broadcasting channel bandwidth of 6MHZ, modulation is used in the 8VSB. it is expected that the U.S. satellite broadcast TV will use QPSK modulation, cable TV will use QAM or VSB modulation.
Since 1995, Europe has issued standards for digital television terrestrial broadcasting (DVB-T), digital television satellite broadcasting (DVB-S), and digital television cable broadcasting (DVB-C). The first consideration for DTV in Europe is the satellite channel, which uses QPSK modulation. European terrestrial broadcasting digital television using COFDM modulation, 8M bandwidth. European cable DTV uses QAM modulation.
Japan's digital TV first considered the satellite channel, using QPSK modulation. And in 1999 released the standard for digital TV - ISDB
The use of digital TV
In digital TV, two-way information transmission technology is used to increase the interactive capabilities, giving the TV many new functions, so that people can access a variety of network services in accordance with their own needs, including video-on-demand, online shopping, distance learning, telemedicine, and other new business
Digital TVs have become a real information appliance.
The most important service provided by digital TV is video-on-demand (VOD), which is a new way of watching TV, it is not like traditional TV, the user can only passively watch the program broadcast by the TV station, which provides a greater degree of freedom, more choices, more interactive ability to pass on the user's needs, to see the user's point of view, and effectively improve the program's participation, interactivity, and relevance. Interactivity and relevance. Therefore, it can be foreseen that the future direction of TV development is towards the direction of on-demand mode. Digital TV also provides other services, including data transmission, graphic broadcasting and Internet access. Users are able to use TV reality stock trading, information query, surfing on the Internet, etc., so that the TV is given a new use, expanding the function of the TV, turning the TV from a closed window into a window of communication.
The connection and difference between digital TV and pay TV
△Digital TV is not equal to pay TV
In fact, digital TV is not equal to pay TV. The concept of digital TV refers to the fact that the whole process of the program from filming, editing, broadcasting, transmitting to receiving is realized by using digital technology. Including digital camera, digital production, digital coding, digital modulation and digital reception, to achieve the purpose of high-quality transmission of television signals. Not only that, digital TV also has rich information business broadcasting function, with interactivity, etc..
From the chronology of the development of digital television, the domestic termination of analog digital signal broadcasting by 2015, during which it is clear that not only the development of pay TV subscribers, the digitization of public **** channel (traditional TV) is also an inevitable trend. And most businessmen currently believe that digital TV is equivalent to pay TV, which is a departure from the reality of development.
△ digital TV can be with the pay TV peer
In fact, digital TV not only can be with the pay TV peer, but also, digital TV and pay TV on the same track is the future development of domestic and foreign digital TV a trend. Adoption of this development model of television stations can occupy the pay TV market, while adapting to the technological trend, and gradually meet the needs of digital broadcasting. In this process, the integration of all kinds of resources to form a new network relationship is extremely important.
Television stations hope to have a digital TV platform through the construction of pay channels, while public channels try to delay digitization, which is conducive to the use of digital TV to achieve the purpose of revenue. And once the time limit set by the government is reached, the open channels can be smoothly transferred to the digital platform.
△Pay TV "content is king"
In fact, the pay TV era more emphasis on "content is king". "The key to the success or failure of pay TV lies in content rather than technology." Li Xiaoming, deputy director of China Central Television (CCTV), asserted this when talking about the prospect of profitability of this business model of pay TV. Digitalization is an unavoidable trend, and as technology matures and advances, the Internet's image and sound transmission level will compete with TV, so TV will lose the advantage of synchronous transmission of video and audio. Therefore, what can really attract the audience is destined to be the content, and will be very different from the previous content. Some industry insiders believe that the people will not pay just to see a clearer program, nor will they pay just because the TV program you broadcast has some simple forms of interaction. "How many people are willing to watch TV while sending money to the set-top box when they can receive a dozen or so channels in a typical area?" Some experts have raised this question. The root of what viewers care about is, after all, the kind of content they get to see, otherwise they won't pay for it. Therefore, it can be predicted that the biggest bottleneck in the promotion of pay TV lies in how to promote the charging model that is directly related to profitability, which in turn depends on the content that is broadcast.
The Prospect of Digital Television
The rapid development of the world's communications and information technology will trigger changes in the entire television broadcasting industry chain, and digital television is a key link in this change. Along with the comprehensive digitization of television broadcasting, the traditional television media will gradually integrate with other means in the field of information and communication in terms of technology and function, thus forming a new and huge digital television industry. This new industry has attracted wide attention, and all developed countries, according to their own national conditions, have respectively formulated the program and industrial objectives for the transition from analog TV to digital TV. Digital TV is regarded as the strategic technology of the new century by various countries. Digital TV has become another major "hot spot" after the IT explosion of telecommunications.
The digitalization of television is another major technological revolution in the history of television development. Digital TV is not only a technical system supported and matched by standards, equipment and program production, but also will have an impact on related industries and promote their development.
What is high definition?
There are many technologies involved in the realization of "high definition," but the simplest and most intuitive expression for the average consumer is that high-definition video provides more detail than the existing television picture. You can get a better idea of what "high definition" means by comparing it to the existing PAL TV standard.
The PAL standard has a resolution of 720 x 576, and in a non-progressive display system, the picture is refreshed at a rate of 50 times per second, which means that each time an odd-numbered line of the picture is displayed, then an even-numbered line is displayed, and then the next frame is displayed. PAL is currently used in domestic TVs and DVDs.
Theoretically, any system that can provide a higher resolution than the existing PAL (or NTSC) system can be called a "high-definition" system. Now the main "high-definition" standard there are two main: the first standard resolution of 1280 × 720, using progressive scanning (Progressive Scan), known as 720p. Progressive scanning can be more stable image, but also conducive to the display of high-speed dynamic picture.
The second standard provides a higher resolution (1920 x 1080), but uses Interlace Scan, known as 1080i, which provides more detail than 720p, but is less suitable for displaying high-speed motion pictures. Both high-definition standards are 16:9 widescreen with a refresh rate of either 50 Hz or 60 Hz. Content providers can choose one of these standards for distributing their video programs, and high-definition TVs process content in both formats on their own.
The standards for TV programs are often differentiated by their vertical resolution (or number of scanning lines) and whether they are progressive scanning or not, so PAL is also known as 576i, while the two high-definition standards mentioned above are referred to as 720p and 1080i. 1080p, which is also a standard often advertised by manufacturers, requires twice the amount of data to be processed as 1080i. 1080i, so it is still limited to applications in high-end systems. Many ordinary consumer color TVs that claim to support 1080p are simply de-interlacing the 1080i signal.