HDTV - Beyond the basics
HDTV - A Closer Look at What Makes HDTV Different
The usual National Television Standards Committee (NTSC) analog TV screen in the U.S. has 525 scan lines, with 480 actually visible. The usual TV has an effective picture resolution of about 210,000 pixels. In the highest resolution digital TV formats, each picture contains about two million pixels. This means about ten times more picture detail on the HDTV screen! On an analog TV the lower resolution is not as noticeable because typically the screen image is constantly changing.
HDTV is part of several standards incorporated in digital television or DTV. Basically, DTV is composed of three separate standards:
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HDTV 1080 (1080 lines of resolution, 16:9 aspect ratio)
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HDTV 720 (720 lines of resolution, 16:9 aspect ratio)
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SDTV (480 lines of resolution, 16:9 or 4:3 aspect ratio)
Of the eighteen DTV formats, six are HDTV formats—five of which are based on progressive scanning and one using interlaced scanning. Of the remaining formats, eight are SDTV (four wide-screen formats with 16:9 aspect ratios, and four conventional formats with 4:3 aspect ratios), and the remaining four are Video Graphics Array (VGA) formats. Stations are free to choose which formats to broadcast.
Formats used in HDTV:
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720p - 1280x720 pixels progressive
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1080i - 1920x1080 pixels interlaced
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1080p* - 1920×1080 pixels progressive
Interlaced or Progressive refers to the scanning system. In an interlaced format, the screen shows every odd line at one scan of the screen, and then follows that up with the even lines in a second scan. Since there are 30 frames shown per second, the screen shows one half of the frame every 1/60 of a second. For smaller screens this is less noticeable. As screens get large the problem with interlacing is flicker. Progressive scanning shows the whole picture, every line in one showing, every 1/60 of a second. This provides for a much smoother picture, but uses slightly more bandwidth.
*1080p is currently the digital standard for filming digital motion pictures. See article: "1080i v. 1080p" in GearWorks by Geoffrey Morrison, November, 2006.
MPEG-2
Broadcasters are having to squeeze the increased picture detail and higher quality surround sound into the same 6-megahertz bandwidth used by analog television. Compression software, very similar to what is used in personal computing, allows this to happen.
Digital TV relies on a compression and encoding scheme known as MPEG-2 to fit its stunning images into a reasonable amount of bandwidth. In each image, the MPEG-2 software records just enough of the picture without making it look like something is missing. In subsequent frames the software only records changes to the image and leaves the rest of the image as-is from the previous frame. MPEG-2 reduces the amount of data by about 55 to 1. MPEG-2 already is the industry standard for DVD videos and some of the satellite TV broadcast systems. Compression reduces image quality from what is seen by the digital camera at the studio. However, MPEG-2 is very good at throwing away image detail that the human eye ignores anyway. The quality of the image is very good, and significantly better than traditional analog TV.
The use of MPEG-2 permits a HDTV receiver to interact with computer multimedia applications directly. For example, a HDTV show could be recorded on a multimedia computer, and CD-ROM applications could be played on HDTV systems. A Digital TV decodes the MPEG-2 signal and displays it just as a computer monitor does, giving it high resolution and stability.
What Does DVI Mean? What is HDCP? What is HDMI? DVI stands for digital visual interface. DVI is an all-digital link between a video/audio source such as an HDTV set-top and a display device such as an HDTV. The DVI link provides an uncompressed digital stream at rates up to 5 Gbps between the two devices. The DVI link does not contain audio, and as such, audio still need to be connected from the set-top to the HDTV or home theatre system. One advantage of DVI is that the link allows graphics to be sent along the link as well. This allows the user interface from the set-top to be displayed on the HDTV. The DVI 1.0 connector and cable on the set-top and HDTV looks as follows:
HDCP stands for High-Bandwidth Digital Content Protection. HDCP is the copy protection standard that is tied to DVI.
HDMI is the next generation of DVI. HDMI stands for High-Definition Multimedia Interface. The main difference between HDMI and DVI 1.0 is that HDMI adds audio to the DVI link and is a smaller connector. The HDMI interface will be backwards compatible to the DVI 1.0 interface, meaning that you can connect up a set-top to an HDTV, where one has DVI 1.0 and the other has HDMI. HDMI in HDTVs has been available since 2004.
See more information on hookup diagrams. |
