Difference between revisions of "HDTV"
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Latest revision as of 17:58, 17 September 2007
What is Digital Television?
Digital Television (also known as DTV or ATSC) is the successor to the aging American analog television standard, known as NTSC. Digital television signals are compressed to a smaller size than analog signals using the MPEG2 codec and are then broadcast. Less bandwidth is used, thus freeing up space of the "over-the-air" (OTA) frequency spectrum. This extra space could then be used publicly or sold off by the United States government.
Because ATSC is a different broadcast standard, all current analog televisions will not receive DTV signals without a tuner/receiver or "set-top box".
The U.S. government has mandated that all broadcasters cease analog broadcasting and switch exclusively to digital broadcasts by February 17th, 2009.
What is Standard Definition Television?
Standard Definition (SDTV) is a digital broadcast signal that is either 640 x 480 pixels, or 704 x 480 pixels and includes stereo sound. Though lacking in resolution, SDTV signals can be sub-divided into smaller sub-channels allowing for multiple streams of video or data (also known as "Multicasting").
What is High Definition Television?
High Definition (HDTV) is a digital broadcast signal that is either 1280 x 720 pixels progressive, or 1920 x 1080 pixels interlaced. Besides increased resolution, other unique features of HDTV are the widescreen 16:9 aspect ratio, and the Dolby Digital sound output.
How do I receive DTV programming?
Digital Television programming can be received in two ways:
- A UHF antenna connected to a digital tuner/receiver. Most new digital televisions have tuners built in. If your digital television is "HD-ready" an external tuner is required.
- Cable or Satellite service. The majority of service providers now offer HDTV programming. A cable or satellite receiver will be required to receive programming.
Digital TV Buyer's Guide
Buying a digital television can be confusing. There are many different technologies and standards to choose from, and a lot of technical details need to be understood so that an independent, informed decision can be made.
EDTV vs. HDTV
When it comes to native resolution, digital televisions come in two varieties: "Enhanced Definition TV" (EDTV), and "High Definition TV" (HDTV). EDTV is 852x480, 1024x768, or 1024x1024; and HDTV is 1280x720, 1366x768, or 1920x1080.
When shopping for a television, always determine what it's native resolution is. HD programming can be viewed on an EDTV, but the programming will be limited to the EDTV's resolution and much of the HD image quality will be lost.
Some digital televisions do not have integrated ATSC tuners to receive HD channels via an antenna; these televisions are labeled as "HD-Ready" or as an "HD monitor". A separate ATSC tuner would be required for over-the-air reception.
Every digital television should have the proper connections for current and future video components. Here are the types of inputs to look for...
HDMI - "High Definition Multimedia Interface" is an all-digital audio/video interface capable of transmitting uncompressed data streams between compatible digital sources like DVD players, cable/satellite receivers, and audio receivers. HDMI will eventually replace older analog input interfaces such as Component Video and be the only connection used by future audio/video devices because it supports the HDCP (High-bandwidth Digital Content Protection) standard. HDMI is backwards compatible with DVI-D. It is recommended that a television have at least two HDMI inputs.
DVI-D - "Digital Video Interface" is a common connection on many digital televisions. Originally designed as a computer-based interface for monitors and projectors, DVI-D is compatible with HDMI devices by using a DVI-HDMI adapter.
Component Video - An analog interface in which video information is sent thru three separate signals: Red, Green, and Blue. For the highest quality possible, always try to use HDMI or DVI connections, unless the device you are using only supports Component video.
VGA - "Video Graphics Array" is the most common analog connection used with computers. Many LCD flat panels offer a VGA input so that a personal computer can be connected. Also known as a "PC In" input.
TV Technology - In Depth
There are many different technologies used in HDTVs
Direct View/Tube: Using a Cathode-Ray Tube, direct-view televisions offer decent picture quality and black level. Although relatively inexpensive, their physical size is cumbersome compared to other newer technologies.
Flat Panel: This revolutionary new type of television has gained popularity due to it's smaller depth then ordinary TVs. Flat panel TVs can be mounted on walls, and placed just about anywhere.
- Plasma - This type of flat panel television consists of tiny phosphors that are activated by the release of neon and xenon gases between two flat panels of glass. Plasma televisions offer fantastic brightness, color, and viewing angles. The biggest drawback to plasma technology is "burn-in". If stationary images (such as channel logos, graphics, or letterbox bars) are shown for extended periods of time, they could become engraved in the display. Luckily, many manufacturers have developed anti burn-in features such as screen savers, and settings that can mitigate the problem. The lifespan of plasma televisions, which was once an issue, has also improved. Many current generation plasmas are rated for 50,000 - 60,000 viewing hours.
- LCD - This type of flat panel television has an array of monochrome pixels, which contain liquid crystal molecules. These molecules are suspended between two transparent electrodes and polarizing filters. The pixel array is placed in front of a light source, and electrical charges determine when light is allowed to pass through, creating an image. Unlike plasma technology, LCD televisions can be produced in sizes below 40". At comparable sizes, LCD often outperforms plasma with regards to native resolution. Many new LCD televisions are now achieving 1920 x 1080 resolution. LCD is immune to burn-in, and can be used with video games or computers without any risk to the display. Keep in mind that LCD has a narrower viewing angle. If viewed from the sides, the image quality will be affected by a significant drop in brightness.
Rear Projection (RPTV): Thinking of going big, but want to avoid paying exuberant prices on a Plasma or LCD flat panel? Then consider a rear projection television. Bulky, "big screen" televisions have been around for decades, but new micro-display technologies have not only improved the image quality of these televisions, but have also reduced their physical size.
- CRT - Cathode-ray tube rear projection had been the standard for "big screen" televisions since their inception. CRT rear projection provides full 1080i resolution, decent black levels, and color. However, these tube RPTVs lack the brightness of micro-display RPTVs. With the advancement of micro-display televisions, CRT RPTVs are quickly disappearing from the marketplace.
- DLP - "Digital Light Processing": microscopically small mirrors laid out in a matrix on a semi-conductor microchip create an image. Each mirror represents a pixel. The mirrors rapidly reposition themselves, controlling the light output. DLP televisions offer good brightness and black level performance. A potential problem with DLP is "rainbow effect". Some people can see brief streaks of color during certain situations, causing headaches. Not everyone is susceptible to this problem.
- LCD - This rear projection format is usually found in entry-level RPTVs. LCD lacks the brightness and black level performance of DLP sets. Although LCD doesn't suffer from the above mentioned "rainbow effect"; a major issue is "screen door effect". When sitting close to an LCD set, a faint grid of pixels is visible, similar to looking through a screen door.
- LCoS - "Liquid Crystal on Silicon": Very similar to DLP, LCoS uses liquid crystals instead of mirrors. Contrary to LCD, liquid crystals are applied directly to a silicon chip and coated with an aluminized layer and a passivation layer. LCoS offers great black level performance, no rainbow or screen-door effect, and provides full 1920x1080 resolution on many models. LCoS tends to cost more than DLP and LCD rear projection. Only two major manufacturers offer LCoS televisions under the following brands: JVC's HD-ILA (Direct-drive Image Light Amplifier), and Sony's SXRD (Silicon X-tal Reflective Display).
Front Projection: If you are looking for a true movie theater expierance at home, a front projector is a must have. Most projectors can accommodate screen sizes from 60" - 120". However, to get the best performance from a projector, you will need a dark, light-controlled environment. Front projectors used to only be accessible to those with tons of cash, but many decent digital front projectors can be found for $999-$2999.
- DLP - These projectors tend to offer better brightness and black-level performance than LCD models. However, just like DLP rear projection, these front projectors suffer from "rainbow effect".
- LCD - This type of projector is not as expensive as DLP front projectors. LCD projectors have decent picture quality and resolution, and offer many features not available on DLP. No "rainbow effect", but "screen door" is still an issue on most projectors. Many companies like Panasonic have introduced features such as "Smooth Screen" technology that reduces this problem.