![[עזרה]](./images/smilies/mit09.gif "[עזרה]"){kind=small}
אני חדש בתחום מישהו יכול להסביר לי בבקשה?הבנתי שיש TV ויש SAT
שלום מה זה HDTV?
-
oriel
- תותח על
- הודעות: 2034
- הצטרף: 25 מרץ 2004, 16:19
אילו תחנות משדרות באיכות כזאת?
The HDTV screen uses a 16:9 aspect ratio. The high resolution images (1920 pixels × 1080 lines or 1280 pixels × 720 lines) allow much more detail to be shown compared to analog television or regular DVDs. MPEG-2 is used as the compression codec. The images are expected to be at least 6 times as sharp as standard definition television or analog television. Like NTSC and PAL, most 1920 × 1080 broadcasts use interlacing to reduce bandwidth demands. Alternating scan lines are broadcast 60 times a second, similar to NTSC's 60 Hz interlacing. This format is entitled 1080i, or 1080i60. In areas traditionally using PAL 50 Hz (1080i50) is also used. Progressive scan formats are also used with frame rates up to 60 per second. The 1280 × 720 format in practice is always progressive scan (with the entire frame refreshed each time) and is thus termed 720p. Several US broadcasters currently broadcast 720p/60 content.
The US digital television system also allows lower, non HD resolutions to be encoded, such as Enhanced Digital Television (EDTV), which is a standard size of 720 × 480 (PAL: 720 × 576) TV picture, only in progressive format, allowing 60 (PAL: 50) full frames per second. Also included is a system for broadcasting Standard Definition Television (SDTV) with the interlacing.
Dolby Digital AC-3 is used as the audio codec, allowing the transport of up to 5 channels of sound with a 6th channel for low frequency effects (the so-called "5.1" configuration). Japanese HDTV broadcasts use MPEG's Advanced Audio Coding (AAC) as the audio codec, which also allows 5.1 audio output. DVB allows both.
Digital HDTV transmission is designed to occupy the same 6 MHz terrestrial band now used in the US for analog NTSC broadcasts. A single NTSC 6 MHz channel can carry 19.2 Mbit/s of information using ATSC's standard 8-VSB (8-level Vestigial Side Band) modulation method. This is sufficient to carry up to 6 standard definition TV channels, or a single HDTV channel. As a side note, the standard for HD signal transmission over digital cable television systems in the US is now fixed as QAM 256 (Quadrature Amplitude Modulation), which is technically part of the DVB standard (but not ATSC) and is a de facto cable industry standard. This method has higher bandwidth than 8-VSB, allowing two 19.2 Mbit/s channels in a 6 MHz bandwidth, due to its lower tolerance for errors which are generally less of a concern in a wired environment. The ATSC standards included a provision for 16-VSB transmission over cable at 38.4 Mbit/s, but the encoding never gained wide acceptance.
Due to technical reasons having to do with the video equipment, recording technologies, and the 19.2 Mbit/s-limited ATSC channel, some HDTV signals will not reach their nominal resolution. Most notably, 1080i60 is impossible to broadcast without artifacts at this bandwidth using ATSC. Most 1080i broadcast signals actually are filtered to 1440 horizontal samples to allow adequate compression, and most current consumer HDTVs based on CRTs cannot resolve even 1440 horizontal samples (most rear-projection CRTs will resolve 1200-1300 at best, unless based on 9" guns). Despite this, HDTV viewed even on existing sets is still far superior to PAL or NTSC in resolution, and future sets are likely to offer superior resolution at the same or lower prices.
The US digital television system also allows lower, non HD resolutions to be encoded, such as Enhanced Digital Television (EDTV), which is a standard size of 720 × 480 (PAL: 720 × 576) TV picture, only in progressive format, allowing 60 (PAL: 50) full frames per second. Also included is a system for broadcasting Standard Definition Television (SDTV) with the interlacing.
Dolby Digital AC-3 is used as the audio codec, allowing the transport of up to 5 channels of sound with a 6th channel for low frequency effects (the so-called "5.1" configuration). Japanese HDTV broadcasts use MPEG's Advanced Audio Coding (AAC) as the audio codec, which also allows 5.1 audio output. DVB allows both.
Digital HDTV transmission is designed to occupy the same 6 MHz terrestrial band now used in the US for analog NTSC broadcasts. A single NTSC 6 MHz channel can carry 19.2 Mbit/s of information using ATSC's standard 8-VSB (8-level Vestigial Side Band) modulation method. This is sufficient to carry up to 6 standard definition TV channels, or a single HDTV channel. As a side note, the standard for HD signal transmission over digital cable television systems in the US is now fixed as QAM 256 (Quadrature Amplitude Modulation), which is technically part of the DVB standard (but not ATSC) and is a de facto cable industry standard. This method has higher bandwidth than 8-VSB, allowing two 19.2 Mbit/s channels in a 6 MHz bandwidth, due to its lower tolerance for errors which are generally less of a concern in a wired environment. The ATSC standards included a provision for 16-VSB transmission over cable at 38.4 Mbit/s, but the encoding never gained wide acceptance.
Due to technical reasons having to do with the video equipment, recording technologies, and the 19.2 Mbit/s-limited ATSC channel, some HDTV signals will not reach their nominal resolution. Most notably, 1080i60 is impossible to broadcast without artifacts at this bandwidth using ATSC. Most 1080i broadcast signals actually are filtered to 1440 horizontal samples to allow adequate compression, and most current consumer HDTVs based on CRTs cannot resolve even 1440 horizontal samples (most rear-projection CRTs will resolve 1200-1300 at best, unless based on 9" guns). Despite this, HDTV viewed even on existing sets is still far superior to PAL or NTSC in resolution, and future sets are likely to offer superior resolution at the same or lower prices.