synonymHD video(HDTV) generally refers to high-definition movies
HDTV (Hign Definition Television), a high-definition movie, uses digital signal transmissionTV programCollection and production ofTV programThe transmission of and the reception of user terminals are all digitized, which is one of the highest standards in digital TV DTV. It stipulates that the corresponding device video must have at least 720p or 1080i scanning,Aspect Ratio 16:9, audio output isDolby digital Format 5.1 sound channel, compatible with receiving signals of other lower formats and performing digital processing and playback.The mainstream HDTV has three formats, namely 720p, 1080i and 1080p.[1-2]
The maximum size of TV set in traditional display equipment is about 50 inches, and the model height ratio of pictures is 4:3 by default. In addition, snowflakes and flickers often appear, which cannot meet people's demand for large screen display.Although later, there are two models that support 16:9 and 4:3Large screen TV, such asPlasma TV、rear-projection tv, LCD TV, etc., but they are also difficult to break the limit of 100 inches. In addition, traditional TV sets are also too large, too bulky, unable to move easily, with large heat dissipation, easily scratched mirrors, mirror reflection interference, and quite expensive.[1-2]
Technical Principles
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HDTV is the abbreviation of Hign Definition Television“HDTV”HDTV technology is derived from DTV (Digital Television) "digital TV" technology. HDTV technology and DTV technology both use digital signals, while HDTV technology is the highest standard of DTV, with the best video and audio effects.[1-2]
DTV is a digital TV technology, which extends from the traditional analog TV technology.The so-called digital TV refers to the use of digital TV signals in all links from the studio to the transmission, transmission and reception, or the transmission of all signals of the system throughBinary digitThe digital stream is formed.[1-2]
To put it simply, the format with a physical resolution of 720p or higher is usually called HD, which is called High Definition in English, or HD for short.Full HD refers to the physical resolution of 1920 × 1080 progressive scanning, or 1080p, which is the top HD specification.[2]
HDTV vs. currentanalog signalDifferent from traditional TV systems, HDTV adopts digital signal transmission.Since HDTV has realized the collection and production of TV programs, the transmission of TV programs, and the reception to user terminalsdigitization。[1-2]
HDTV stipulates that video must have at least 720 line non interlaced (720p, commonly known as progressive) or 1080 line interlaced (1080i, commonly known as interlaced) scanning (DVD standard is 480 lines),Aspect Ratio It is 16:9.The audio output is 5.1 channels (Dolby digital format), and can be compatible with receiving signals in other lower formats and performing digital processing and playback.[1-2]
Display requirements
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format
HDTV has three display formats: 720P (1280 × 720, non interleaving, field frequency 24, 30 or 60), 1080i (1920 × 1080, interleaving, field frequency 60), 1080P (1920 × 1080, non interleaving, field frequency 24 or 30), but basically it only inherits the algorithm of analog video, mainly to correspond to the original TV video definition standard.For true HDTV, there are only two standards that determine the definition: resolution and encoding algorithm.Among them, 720P and 1080i are the most common ones circulating on the network, while 1080P samples are relatively large on the Microsoft WMV-HD site.[1-2]
The US HD standard mainly has two formats, namely 1280 × 720p/60 and 1920 × 1080i/60;Europe tends to 1920 × 1080i/50;With 720p as the highest format, the required line frequency support is 45kHz, while the 1080i/60Hz line frequency support only requires 33.75kHz, and the 1080i/50Hz line frequency requirement is even lower, only 28.125kHz.[1-2]
Among the three formats of HD signals, 1080i/50Hz and 1080i/60Hz have exceeded 1000 lines in the number of scan lines, but they all use interlaced scan mode. 1080 lines are completed by two scans, and only half of the actual number of scan lines per field is 1080/2=540 lines.Because a complete picture needs to be displayed by two scans, this interlaced scanning technology is limited in principle, and slight flickering and crawling still exist when displaying fine pictures, especially still pictures.But 720p/60Hz is different. It adopts progressive scanning mode. A complete picture is displayed at one time. The number of lines in a single scan can reach 720 lines, and the horizontal scan can reach 1280 points;At the same time, because the field frequency is 60Hz, the picture is stable and clear without flickering[1]。[2]
HDTV resolution is 1280 × 720 and 1920 × 1080, which is really a big challenge for today's displays. If the resolution is further improved, it will be difficult to obtain better image quality on existing displays, because the bottleneck at this time is the display device.For screens below 32 inches, the 1920 × 1080 resolution has basically reached the human eye's resolution limit for dynamic video definition, which means that no matter how high the resolution is, it can only show advantages on large screen displays.[2]
code
In addition to the resolution is the key to HDTV, the coding algorithm can not be ignored.HDTV can be basically divided into three algorithms: MPEG2-TS, WMV-HD and H.264. Different coding technologies naturally differ in compression ratio and image quality.In contrast, MPEG2 TS has a poor "compression ratio", while WMV-HD and H.264 are more advanced.The encoding technology with poor "compression ratio" also has low requirements for decoding environment, which means that the requirements for hardware equipment can be reduced.[2]
Basic characteristics
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HDTV has extremely high definition, resolution up to 1920 × 1080, and frame rate up to 60fps.In addition, the screen aspect ratio of HDTV has also changed from 4:3 to 16:9. If you use a large screen display, you will feel like you are in the cinema.At the same time, due to the use ofdigital technique The signal anti noise ability is also greatly enhanced. On the sound system, HDTV supportsDolby 5.1 channelTransmission, bringing people Hi Fi level hearing enjoyment.andanalog televisionIn contrast, digital TV has high-definition picture, high fidelity stereo sound, TV signal can be stored, and can be completed with a computermultimedia system , full utilization of frequency resources and many other advantages will inevitably promote HDTV to become the main force of home theater.[1-2]
HDTV is characterized by high definition, while most display devices such as rear projection, liquid crystal, plasma, etc. may not be able to achieve the resolution of signal source, that is, display devices cannot play the advantages of signal source.According to the survey, the display device that can perfectly display HDTV is a projector, and the player's most desired playback device is also a projector.The biggest advantage of the projector is its large screen, which can easily reach more than 100 inches, and its visual impact is very strong.Most video projectors only support 720p and 1080i resolution formats, while a few can support 1080p resolution formats.But even the 720p projection picture is much clearer than DVD, which only provides 480i or 480p format output.[1-2]
application area
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As a new generation of display equipment, projection has been widely used in China's education and business fields, and has shown great development potential in the home market.Its advantage lies in high image quality. The projector has been able to output 1080i, 720p or higher signal formats, and can be compatible with different signals downward;Large screen display, the projector can easily achieve a large screen display of more than 100 inches;And there is an advantage that no TV can match, that is, the size of the projection picture can be adjusted at will, and it can be moved at will.Therefore, the marriage between HDTV and projector is unstoppable.[1-2]
