HDTV Basics
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You may not be thinking about buying a new TV. But some time in the future, you will. 
What this means for the consumer is – ‘Know … Before You Go’. But Where To Start? Consumer Choices To commence, let’s notice at some of the different options you have; NTSC Analog TV – (National Television Standards Committee), Traditional TV; ATSC Digital TV – (Advanced Television Standards Committee), DTV; Integrated HDTV – or simply, HDTV; DTV with an Internal (built-in) High Definition TV Receiver. Digital-HDTV-‘Capable’ or ‘Ready’- Digital TV that is able to DISPLAY HDTV – BUT ONLY EDTV – Enhanced Digital TV – a classification* describing Digital TV’s that are basically ‘high-end’ SDTV’s. While these often include some type of technical features, added by the Manufacturer to enhance the picture, nevertheless, the picture quality does NOT equal HDTV. Technically, there is virtually no visual difference between an SDTV and an EDTV – with the possible exception of the higher price. Different TV Demonstrate Types: Direct-view – Images displayed directly on the picture tube (as in the traditional CRT – Cathode Ray Tube) or one of the new, alternative technologies with a “fixed pixel” screen; ie: LCD (Liquid Crystal Display); Limited Display Size – maximum range, about 40-inches. RPT – ‘Rear Projection TV’ – uses multiple, miniature picture tubes, (commonly 3) or pixel display, and a combination of mirrors and lenses to project the image from behind, on to the viewing screen; enables displayed picture to be significantly larger; size ranges: 43 to 70+ inches). Offers best value – picture size and quality at lowest cost. FPT – ‘Front Projection TV’ – Projects images forward, to an external screen; more commonly ancient in Home Theater Systems for displaying DVD Movies; for DTV/HDTV may require purchasing TV components separately – including, TV Receiver, A/V Receiver, Display Veil and Speaker System. Complete Systems can be extremely costly, and may require professional installation. Enables an almost unlimited display size. Different TV Display Technologies: CRT (Cathode Ray Tube): Ancient TV Technology – The established standard for television displays; best overall value – picture quality and cost; major drawback is bulk and mass as size increases. Plasma Display – Ultra-Thin form, High Contrast Ratings, ‘Fixed Pixel’ Display; Size up to 60+ inches; some display limitations – costly, high burn-in risk; picture quality affected by inability to display black-color; displays are extremely heavy and fragile; describe quality lost as pixels fade; many Plasma Displays do not display HDTV resolutions. Development continues. LCD – Liquid Crystal Display; Thin design, size limitations; good computer monitor; sharp picture for static displays; problems displaying images in motion; many LCD Displays are not HDTV satisfactory. Development continues. LCoS (Liquid Crystal on Silicon) – Improved LCD Technology, may hold promise for future HDTV display; costly; manufacturing problems continue; development ongoing. DLP (Digital Light Processor) – Uses Chip and Software Technology – entertaining, alternative display technology; well-behaved HDTV display; eliminates most short comings of other technologies; moderate cost; some viewers query “softer” describe, and use of “color-wheel;” promising future – development continues.
Digital TV (SDTV) programs can be in either 4:3 or 16:9 aspect ratio. TV Monitors of either aspect ratio can indicate programming with a different aspect ratio; however, this will affect the way the narrate is configured on the screen. We will discuss aspect ratio in greater depth, later on. As these options show, right from the initiate, the consumer has a number of decisions to make, long before making that final purchase decision. Examples: Aspect Ratio – width to height (4:3) or (16:9); refers to the TV Display and to TV Programs. Picture Resolution – 720-p; 1080-i; 480-i/p; – and recently added, 1080-p. Progressive Scan – display method (“p” in 720-p) Interlaced Scan – indicate method (“i” in 1080-i) D/A – A/D – digital to analog and analog to digital converter STB – Set-top Box (aka: Receiver, Tuner, Decoder or Descrambler) OTA – ‘over-the-air’ or ‘off-the-air’ – refers to Local TV Broadcasts (These are unbiased a few examples of the original terminology you will approach across. For a more complete list of Digital-HDTV definitions, please refer to the separate part under the heading: Digital-HDTV Glossary) The Digital Enigma Added to the complexity of Digital-HDTV, and all the confusion generated by the Digital Transition – as if these were not enough – are some perplexing contradictions. It is easy to get entangled in a web of paradoxes. A visit to the local electronics Super Store is likely to confirm this. Try asking any basic questions you may have – about the transition to Digital Television; or what the difference is between SDTV and HDTV; or what is needed to have High Definition TV reception in your home. Then compare the different answers – and/or lack of any coherent response. Note: To be splendid – there have been some new improvements regarding available information. It can only be hoped, that by the time you read this, more accurate information will be readily accessible. But counting on this would not be a wise bet. Second – In stark contrast, at the opposite extreme, is the continuous flow of ‘misinformation’ and ‘disinformation.’ This flood of unreliable information has inundated the general public. The path to useful and reliable information is littered with inaccuracies, fallacies and myths. And this is further aggravated by misleading advertising and marketing ploys. As an example, here’s a question asked repeatedly by perplexed consumers concerning the transition from Analog TV to Digital TV: Okay, that’s really two questions… Principal NOTE: The FCC’s mandatory transition from Analog TV to Digital TV does NOT refer to, nor mean ‘High Definition Television!’ This highlights one of the primary sources of so much of the public’s confusion concerning Digital TV and HDTV. These are two discrete terms, yet they are frequently used incorrectly – as if they were interchangeable words with the same meaning. They are NOT the same; they designate two distinctly different classifications of television.| High Definition Television is ‘digital’; however, HDTV is just one (1) of eighteen(18) ‘Digital TV Formats’ designated in the ATSC Standard. In reference to the second fraction of the above question: “When will this transition be completed? ” Considering that a number of interim “deadline” dates have been extended, not enforced or simply ignored, it leaves in doubt whether or not the 2006 deadline will be upheld. Thus, the actual “STOP” date for analog TV remains uncertain at this time – (early 2005). The general consensus at present is that the transition to Digital TV Broadcasts will not be completed by the scheduled date. Unfortunately, you cannot count on obtaining the information you need about digital-HDTV from the average ‘Sales Associate’ in your local Electronics Store. While you may be fortunate enough to find a sales-person who happens to be knowledgeable about Digital TV, and may even know the difference between DTV, SDTV and HDTV – the odds are not in your favor.
Now it’s time to perceive at how ATSC (Advanced Television Standards Committee) Digital Television (DTV) differs from traditional, NTSC (National Television Standards Committee) Analog TV Originally, the standard NTSC Analog TV received the transmitted video signal from a Local Broadcaster. But a major quandary with analog signals is that between the transmitter and your TV station many things can interfere, thus distorting the picture displayed on the Cover. From a plane flying far overhead, to hilly terrain, tall buildings and even weather and atmospheric conditions, all are obstacles that can interrupt the signal. Also, the strength of the analog signal is critical. A weaker signal can cause “snowy” and distorted pictures; the weaker the signal the more likely it will be affected by interference – something with which any of us who can remember “pre-cable TV” are only too familiar. The Digital Difference A Digital TV receiver isn’t concerned with signal strength, or what conditions exist between your set and the transmitter. As long as the signal gets to the receiver, and the code can be read, the Digital TV is able to reproduce a near-perfect picture – virtually identical to the original, back in the TV Studio.
A distinct advantage of digital broadcasting is that bad reception is a thing of the past. One reason Cable TV caught on is because it delivers clear TV pictures without regard to the viewer’s residence. Viewers don’t have to be constantly adjusting the antenna in an attempt to “tune-in” a weak signal from a distant transmitter to get a distinct picture.
This might be compared to sending Morse Code. As long as the person at the other destroy can design out the dots and dashes being transmitted they will be able to read the message. Once they lose the distinction between a dot and a dash they lose the message. Digital TV acts the same way; instead of sending dots and dashes, it sends millions of (1′s) and (0′s) every second. As long as the TV Receiver can read the (1′s and 0′s) it displays a virtually perfect picture. The bottom line … you either receive a 100% quality image, or nothing at all. Adding an “H” to ‘DTV’ = W O W! It is important to brand that the focus up to this point has been on DTV – digital television – in general. High Definition Television is digital television – BUT … Note: Unfortunately, you will likely confront mis-information stating that Digital TV in various configurations is ‘high definition television.’ This is NOT Proper! You may also be told that as long as the TV meets one or two criteria, or if it has been enhanced by the Manufacturer, using some proprietary engineering “magic,” this makes it – “as satisfactory as” – HDTV. Again, NOT TRUE! In considering Digital-HDTV, it may be helpful to treat any information you come across, the way that Governments handle relations with Foreign Countries – “Trust … BUT VERIFY!” How do you know if it is – HDTV? The image you see on your television screen is comprised of a series of horizontal lines. An electron gun ‘shoots’ energy beams (light) which strike a layer of phosphor on the inside surface of the picture tube, causing it to glow. These glowing lines create the image displayed on your TV screen. How they are formatted, which resolution is broken-down, what standards are met, are some of the factors that determine the type of television picture you will receive. Resolution Designate – although it is the horizontal lines that are counted, this is referred to as “vertical resolution” because the lines are counted from top to bottom – or vertically.
Note: More details about TV Resolution can be found in a separate section under the heading, Different TV Display Methods: Interlaced and Progressive Scan There are two methods that can be used to display the lines on the screen – either “Interlaced” or “Progressive Scan.” The NTSC adopted the standard known as “interlaced” to provide a method of compression that achieves a higher resolution using less-costly circuitry. In using the “Interlaced” method, the 480 lines are created in two fields (phases). The “scan-rate” for these (2) fields is 60hz (60 times per second). In Phase #1, the first 1/60th of a second, 240 lines (the odd numbered lines – 1,3,5 etc) are scanned on the tube. In the second 1/60th of a second, (phase #2)- the remaining 240 (even-numbered) lines are scanned. Progressive Scan Digital TV also has formats that use the interlaced system; however, DTV also uses another system, called “Progressive Scan.” The progressive system scans the total number of lines, 60 times a second; not half and half as in interlaced. This means you see the complete image displayed on your TV screen two-times more often. This results in smoother motion; moving images have less ‘motion artifacts’ with none of the visible “flicker.” A progressive scan system with 480 lines of resolution is written, “480p.”
Note: 1080i displays more lines and thus delivers more information. This produces better “spatial resolution” – producing sharper pictures when the image is “still” or has little motion. Manufacturers have generally preferred the Interlaced format because more lines of resolution can be delivered with less bandwidth, resulting in lower costs. Both sides in this (i/p) debate are dug-in, with ardent supporters and aggressive detractors abounding on each side. But which is the better system is a subjective determination. You might say “it’s in the eye of the beholder.” However, the introduction of 1080p should bring this debate to an demolish. The different television networks have individually selected the particular DTV format used by their respective networks for transmitting High Definition Television broadcasts. For instance, ABC and the FOX Network chose to utilize 720p; while CBS and NBC transmit in 1080i. The important note for consumers concerning HDTV resolution, is that the TV is capable of converting incoming signals to whatever the set’s native resolution is; this allows viewing all TV signals in the set’s designated (native) format. High Definition Television displays pictures that contain significantly more detail, resulting in much ‘crisper’ pictures. Images viewed on TV screens are made up of little picture elements known as ‘pixels.’ Each of these pixels is made up of three, closely spaced ‘dots’ of color – red, blue and green. Combined together on the TV’s phosphor hide, and viewed from a distance, the colors are seen as one. The phosphor at each of these dots emits light directly proportional to the intensity from the electron beam that hits it, as it scans across the screen. On stale, NTSC TV’s 256 levels of intensity are possible for each of the three colors. The result is a range of 16.8 million colors for each pixel. The pixels in the analog system are slightly ‘taller’ than their width. Get up close to an analog screen – especially the larger projection sets – and you can easily search for the red, blue and green rectangles. This is why distortion is sometimes seen on faded, NTSC TV’s.
DTV sets are sold in two ‘Aspect Ratios.’ Aspect Ratio refers to the ratio between the horizontal (width) measurement and the vertical (height) measurement of the screen. This ratio is also used in reference to how the picture is transmitted and displayed on the screen. The two aspect ratios used in DTV are (4:3) and (16:9). That is, (4) units wide by (3) units high, and (16) units wide by (9) units high respectively. Your NTSC-analog television has an aspect ratio of (4:3); the shroud appears almost ‘square’ because it has just slightly more width than height. For instance, a (4′) wide screen would have a height of (3′).
The ATSC adopted the 16:9 “wide-screen” aspect ratio as the standard for Digital-HDTV, because significantly more information can be displayed on the screen. And Wide-screen DTV/HDTV sets appear more ‘rectangular’ than the familiar ‘square’ shape of your NTSC-analog set. (Don’t confuse this with screen “size,” which is the screen’s diagonal measurement) Wide Screen Display – Why? In 1941, when the NTSC proposed the standards for broadcast television they had no reason not to adopt the same 4:3 ratio faded by the film industry. And it was a later benefit as TV producers began telecasting movies filmed in the format. In the 1950′s, Hollywood found they needed to provide the public with a specific reason to buy movie tickets, since people found it preferable to sit home and enjoy free television, rather than pay to see a movie. In addition to trying innovations like “3-D” movies, the studios experimented with aspect ratio; “Cinemascope” was one of the early ‘wide-screen’ ratios that can unruffled be seen today. The reasoning that led to wide-screen formats is simply that the wider view is closer to the human field of vision. And because the viewer is visually drawn into the action more with wide-screen, the enjoyment level is enhanced. Our vision is optimized within a 30-degree field of vision. We examine details best within the ‘center’ situation of this field, while our peripheral vision is better at detecting motion. Beyond 30-degrees there is no visible benefit. The familiar 4:3 ratio allows us only a 10-degree field of vision. In the theater, ‘wide-screen’ formats were easy to reproduce by using more or less of the state projected on the screen, as needed. However, as movies were displayed on TV screens, and later made into videos, the aspect ratio became more complicated. Initially, movies were ‘cropped’ to ‘fit’ 4:3 analog-TV sets. However, reducing the image height requires removing some information that leaves a portion of the vertical area ‘blank’; this appears as a black ‘Bar‘ on the screen. The image is displayed in the center of the screen, with the blank area divided into two, horizontal, black ‘bars’ across the top and bottom of the screen. These bars increase or decrease, as the aspect ratio changes. However, ‘letter-boxed’ movies, originally filmed in extra-wide format, can be especially troublesome when viewed on smaller TV screens, due to the extremely reduced viewing area. Letter-box and Window-box When you watch a program that is transmitted in (4:3) aspect ratio, on a (16:9) shroud, the image will be “window-boxed” – centered on the screen with vertical unlit bars (gray on some models) on both sides of the picture. When you watch a (16:9) program on a (4:3) hide, it will appear letter-boxed (previously described) with horizontal bars across the top and bottom of the screen. This brief introduction to Digital-HDTV Basics, provides a (simplified) overview of how DTV differs from traditional Analog TV, and how HDTV differs from Digital-SDTV; and a little about the Transition from Analog TV to Digital TV. (Refer to the HDTV Buyers Guide for more details on what to consider before buying a Digital-HDTV) |
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