The High-Definition Itch

Published Date
01 - Jan - 2007
| Last Updated
01 - Jan - 2007
The High-Definition Itch

You might be not able to afford one. There is nothing to watch on one. But you still want one. We help you scratch that HDTV itch

There is no clear path to HD land. The idea of high-definition television is a beehive of activity with new tech replacing the old, faster than a speeding bullet. With no clear winner, choices are numerous, with many pros and cons to weigh. Things are not very clear on the content either: HD content producers are ambiguous on their DRM (Digital Rights Management) policies-will they, won't they, and when (because they will)? What resolution will be widely adopted, to what extent will DRM shackle our media? To make matters worse, the content sources are anaemic in India (neither over-the-air nor broadcast HD channels available); the only HD content currently on offer being games. Nor is there any clarity on the next-generation of HD media-will Blu-Ray best HD-DVD or vice-versa?

But walk into an electronics shop and your jaw drops-pretty HDTVs all in a row and none of the above matters, lust overtakes logic; and while some practical corner of your brain pleads to look before you leap into the HD stream, you can't help but scratch that big-screen itch.

So, hearts filled with joyful consumerism, let's take a walk through the HD swamp-learn a bit about what makes an HDTV, and take a look at some of the numerous technologies available, with a strong emphasis on the pros and cons of each. Which technology to pick? There is no clear answer. Consider this an interesting journey without a destination.

What Makes An HDTV?
All televisions display images as a grid of coloured dots or pixels. The more the dots a TV can display, the higher its resolution. The TV sets that most of us currently use is called SDTV; it has the lowest resolution possible. An enhanced version of this type of TV-called EDTV-is also available, but even that type does not differ much over the SD variety. The drawback of a low resolution is that as the screen size of a television set increases, the TV has to fit the same number of pixels to a larger screen area. This results in poor image quality; it's similar to watching a video recorded by a cell phone on a PC in full-screen mode. Larger displays offer a more cinematic experience. This is where HDTV steps in.

TVs generally come in two screen ratios-a 4:3 screen and a 16:9 screen; some sets also sport a 16:10 screen. The number denotes the ratio of the horizontal size of a TV screen to its vertical size. Thus a 4:3 PAL SDTV (the most common variety) uses a fixed pixel grid of 768 × 576 or 720 x 540. Most movies, however, are shot in 16:9 format, also known as widescreen (as seen in movie theatres); some SDTV sets and almost all HDTV sets come in a 16:9 widescreen format. A small thing to note: if you are in the market for a new PC monitor, you'd do well to pick up a widescreen variety, as most forms of entertainment now come in 16:9.

Now what happens if your TV is not 16:9? The 16:9 format movie on a 4:3 TV set will be scaled down to fit the lesser width. This leads to empty areas at the top and the bottom of the TV screen, which are filled with black bars. This is known as letterboxing. Some sets might attempt to stretch and scale the image and make it fit the 4:3 area, leading to a distorted video. Others might zoom into the video instead; this hides a portion of the video content. A 4:3 format video on a 16:9 display will fill the screen from top to bottom but not from the sides, and so you will see borders on either side of the screen.

As a general rule of thumb, all HDTV sets are likely to be widescreen, but all widescreen TV sets need not be HDTV. Thus what essentially distinguishes an HDTV from an SDTV is its screen resolution. An SDTV is 480i, an EDTV is 480p, and HDTV can be either of three resolutions: 720p, 1080i, 1080p. What do these specifications mean? The number denotes the number of horizontal lines of dots that are present in the TV. Thus a 480i has 480 lines forming its screen. An HDTV resolution is 720 and above-720p, 1080i, and 1080p-since an HDTV is widescreen and 16:9, these numbers correspond to 1280 x 720 and 1920 x 1080 pixels. The "i" stands for "Interlaced," the "p" for "Progressive." This is a way to denote how a picture is painted on a TV screen.

HDTV: Looks good, feels great

Interlaced TV sets, which most of our TV sets are, divide a video image into odd and even lines of dots. Each divided image forms a field, and when the odd field and the even field are combined, they form a complete frame. An interlaced TV draws each field every 1/60 of a second to form an illusion of running 30 frames every second. The illusion, however, isn't perfect, and almost everyone can perceive flicker on our standard TV sets. A progressive scan TV set takes both the fields and combines them before displaying on screen. It thus displays a complete frame every 1/60 of a second-painting a complete picture at once, to eliminate the flicker. Progressive is almost always superior to interlaced.

Beware: some TV sets offer SDTV/EDTV resolutions along with 1080i-these are not HD sets; make sure your HDTV offers at least a 720p resolution.

Almost all HD sets available in the market today are 720p/1080i; 1080p sets are a newer breed and are much costlier than a 720p set. Generally, a 720p set can also do (or is advertised) as 1080i as well.

So which one should you buy? For all practical purposes, a 720p set is good enough. All HD content-movies, over-the-air TV content, or games-is enjoyable on a 720p set. More is, of course, better, but a 1080p set is not only significantly costlier, there is little HD content available in 1080p to best utilise the set. Subjectively, for lower screen sizes or larger sitting distances from the TV screen, it becomes very difficult to qualitatively differentiate content on a 720p set from that on a 1080p. Unless you are buying a set larger than 50 inches, you need not concern yourself with the lack of 1080p resolution.

Now that we're clear on the basics of TV and HDTV, let's move on to the specifics of what makes a High-Definition television.
HDMI Demystified
Our usual cables need not apply to the new HD era: S-video, SCART and composite cables are not suited for HDTV viewing. They simply do not have the required bandwidth, nor do they offer the required digital fidelity. When you move on to HDTV, you will have to deal with component, DVI and HDMI cables. The latter two are digital in nature and are the ideal course to take. A component cable will carry unprotected HD content. Most of the high-definition content will be protected, and to view this as intended, you will need HDMI ports on both the source of content (unless it's over-the-air) and on the TV set. HDMI (High-Definition Multimedia Interface) is a pure digital cable that carries audio and video and is backward-compatible with DVI-D-a DVI-D source can drive an HDMI unit through a converter, but the audio will not be available. As for the content protection: HDCP (High-Bandwidth Digital Content Protection) is a form of DRM (digital rights management) that controls content travelling along DVI-D and HDMI. High-definition video content is downgraded to DVD quality on non-HDCP compliant TV sets, when requested by the source. DVD-Audio content is restricted to DAT quality on non-HDCP digital audio outputs (analogue audio outputs have no quality limits). Thus you will need an HDTV with an HDMI port, a video source with HDMI output, and an HDMI cable to experience real HD content.
HD-DVD and Blu-ray Disc players allow movie studios to set an Image Constraint Token (ICT) flag that will only output full-resolution HD content through HDCP. If such a player is connected to a non-HDCP-enabled HDTV, and the content is flagged, the player will output a 480p signal. The good news is that most of the movies studios seem to have informally agreed to not use this flag for the near future; additionally, none of the HD games currently have any restrictions-they can be enjoyed over both component and HDMI without niggles.

One Big Family 
The majority of HDTV sets, be they LCD, plasma, rear-projection microdisplays, DLP, or LCoS technology, are so-called fixed-pixel displays. Such a display uses pixels to form images. Non-fixed-pixel displays are direct-view and rear-projection CRTs, and they don't use discrete pixels to display images. Fixed-pixel HD displays operate at a "native" resolution, say 720p. They are also all inherently progressive-scan-even a 1080i "interlaced" HDTV set runs at a 720p "progressive" resolution. Since an HDTV only talks in native resolution, there is some scaling involved with content: no matter what the source of the content, a fixed-pixel HDTV will always scale it to fit to its native resolution.

HDMI to DVI-D adapter

If the incoming signal has more pixels than the TV can handle, you will lose some detail and sharpness. If in turn the signal has fewer pixels, the TV will scale it to fit its screen but you won't get any extra detail and sharpness (this is called upscaling or upconverting). How well the TV does at scaling is a critical point to consider while purchasing an HDTV.
Before making a purchase, we recommend that you play various content on your desired set-TV, DVD, HD video games, and if available, HD movies.

What Flavour HDTV? 
Wouldn't it be great if you could just walk into a store and pick up an HDTV, any HDTV, without worrying about black levels, contrast ratio, refresh rates, viewing angles, colour saturation, colour accuracy and so on… of course it would, but if you're in the market for an HDTV, you need to understand the pros and cons of each HDTV technology.

Broadly speaking, there are two major categories of HDTV-you have your Flat Panel TV sets, which are your thin plasmas and LCD panels. Then you have your rear-projection sets which can be LCD, DLP (Digital light Processing), CRT, or LCoS (Liquid crystal on silicon). Apart from these, you can also purchase an HD-resolution projector, or an old-fashioned CRT TV set. Let us run through the major technologies first, and then take a look at the table Which HDTV Should I Buy?

Flat Panel Displays
There is little to differentiate between a plasma and an LCD display today-each one's pro is generally replicated well by the other. A plasma screen is no longer as liable to suffer from burn-in as it used to, while an LCD TV's viewing angle is much improved today than it was a year ago. And so on. Generally speaking, a plasma television is still a better choice if you are looking to set up a home-theatre: these are large screens with great image quality, high brightness, and good contrast ratio. The only negative is screen brightness: a plasma TV will gradually dim over its life. Present plasmas are typically 60,000 hrs of half-life-long enough to last five to six years, but something to keep in mind while picking one up. For gaming, both technologies have their cons: an LCD screen is liable to "ghost" or blur when the action gets fast (due to slower response time); a game's HUD (Head-up Display) is liable to be burned-in to a plasma screen. Both these display types are widely available in the market, and unless you are a videophile, picking up either of these technologies is a safe choice.
Rear-Projection TV
Microdisplays make up most rear-projection units. A microdisplay is driven by one or more microchips, which contain millions of pixels. Based on the nature of the chip, a microdisplay can be further classified as DLP, LCD, and LCoS. Each such unit displays by either bouncing light on to and off these chips (DLP and LCoS) or streaming light through them (LCD). The light source, being a lamp, must be replaced every 5,000 to 10,000 hours depending upon the technology and model (ask your local dealer for details); the lamps might also require a few seconds to warm up and cool down. Due to the nature of the technology, all such TVs are excellent for viewing in bright rooms. Let's quickly run through two of the most promising microdisplay technologies:

DLP: The microchip is actually an array of mirrors sitting on silicon, the number of mirrors correspond to the resolution of the set. These mirrors are rapidly repositioned to give various shades of grey by varying the intensity of light through a lens; black and white levels are achieved by switching the mirror off and on respectively. Colours are added by use of either a colour wheel, or by employing Red, Green, and Blue LEDs. A common complaint about DLP sets is that of the "rainbow effect"-this artefact is generally visible as a multi-colour shimmer when changing focus from one part of the projector screen to another, generally at a viewer's periphery when shifting focus from a high contrast area or bright object. The rainbow effect is mostly seen in single-chip DLP projectors. Make sure you check for this before buying a DLP set-people are not equally sensitive to the effect.

Some DLP sets use a technique called "wobulation" to double the actual resolution of a TV-a 1080p chip might have 960x1080 physical pixels. A mirror or lens is then made to move rapidly to form a complete picture, from the two halves of 960 pixels to give the 1920 x 1080 (1080p) finished picture. A wobulated image might appear soft; results vary from set to set.

 Ideal sitting distance from an HDTV set

Screen size                            Viewing distance
    30"                                       3.75 to 6.25 feet
    34"                                       4.25 to 7 feet
    42"                                       5.25 to 8.75 feet
    50"                                       6.25 to 10.5 feet
    56"                                       7 to 11.75 feet
    62"                                       7.75 to 13 feet
    70"                                       8.75 to 14.75 feet

What is an "HDTV-ready" TV?

Some HDTVs might not have an inbuilt tuner to view over-the-air or broadcast HD content; these are generally labelled as "HDTV-ready TV" and must be connected to a separate HDTV set-top box to view them. Note that they will have the usual PAL/NTSC SDTV tuners

HDMI Cables

LCoS: This is a technology similar to DLP, but uses liquid crystals instead of mirrors to reflect light. LCoS is the technology to watch-it has the potential to realise big-screen HDTVs with very high picture quality and at a low cost compared to the others. Pixels on LCOS panels can be made smaller than is possible with other microdisplay technologies, without compromising on picture quality or manufacturability. LCoS displays can be scaled to 1080p resolution and beyond, without increasing the size and cost of the panel and other optical components in the light engine. Commercially, Sony's SXRD is the most visible and viable implementation of this technology in the market.  

Ahmed ShaikhAhmed Shaikh