Chapter 2: HT Video

Certainly the TV is the central part of any HT system. This chapter will tell you about some of the important concepts and technologies behind TVs and end up giving you what you need to start shopping if you decide your current TV won’t do.

Understanding Resolution

If you look closely at a TV screen, you can see that the picture isn’t smooth and uniform, but is rather made up of numerous dots. By “numerous,” I mean about 300,000 or more.

If you step back from the TV, your eye can no longer see the dots, and the picture looks continuous. That’s the minimum viewing distance at which you can comfortably sit. The problem is that at that distance the TV picture is pretty small. It’s much smaller than the picture on the screen of a movie theater from where you normally sit, even it you sit fairly far back.

This is one of the main obstacles to getting what we want out of HT: A small picture just doesn’t make it seem like we’re at the movies. The obvious thing to do is to get a bigger TV, but that might not work—the dots might just be bigger, and the picture will still look lousy. Worse, you might not be able to get far enough back if the TV gets really big.

To learn what’s behind this difficulty and how to fix it, we need to understand what’s called resolution, which is the technical term for the number of dots in some given span. As you read on, remember that the higher the resolution, the smoother and sharper the picture.

How TV Resolution is Measured

On TVs resolution is measured by imagining the biggest circle that can be drawn on the screen and then counting the dots along the vertical and horizontal diameters of the circle, as shown in Fig. 2-1.

That’s the way it’s supposed to be, anyway. Some TV manufacturers measure the horizontal resolution all the way across, even though that’s wrong, because that’s what most buyers think horizontal resolution is and, more importantly, it gives a higher number. (Computer-screen resolution is measured all the way across, which is perhaps why there’s so much confusion.)

In this book, I’ll use TV resolution correctly and consistently, so that our comparisons of various things will make sense. But when you go shopping, be careful.

With TVs resolution is usually given in terms of lines instead of dots, since a row of dots forms a line, and I’ll use lines from now on. So you don’t get confused, remember that the vertical resolution is the number of horizontal lines, and the horizontal resolution is the number of vertical lines. Every time I give a number for the resolution in one direction or the other, I’ll put a V or H after it, to remind you which it is. (For example, 480V, a measure of vertical resolution, is the number of horizontal lines.) That’s not typical notation that you’ll find outside of this book, but I’ll use it anyway.

The next two sections discuss vertical and horizontal resolution separately and in a bit more detail.

Vertical Resolution: NTSC, PAL, SECAM, and HDTV

Today, there are three main standards in the world for TVs. They apply to broadcast, cable, satellite, videotape, DVDs, and all other sources of TV video:

·      NTSC (“National Television System Committee”). Used in North and South America, Japan, South Korea, and Pacific islands.

·      PAL (“Phase Alternation by Line”). Used in most of Western Europe, Africa, Asia (except Japan and South Korea), and Australia.

·      SECAM (“Sequential Couleur Avec Memoire”–sequential color with memory). Used in France and Eastern Europe.

A TV for one standard can’t play a source in a different standard, which is why, for example, gift shops often sell two or even three kinds of souvenir videotapes.

The vertical resolution of an NTSC TV is fixed at 480V lines, and PAL and SECAM vertical resolutions are fixed at 576V. Thus, there’s no point comparing the vertical resolutions of various makes and models of TVs of a given standard, because the number is fixed.

HDTV (high definition TV) is a newer standard that provides for much higher resolution than the others. There’s more about it in Chap. 5; for now we’re only concerned with the two new vertical resolutions it offers: 720V lines and 1080V lines.

Horizontal Resolution of TVs

Horizontal resolution, unlike vertical resolution, isn’t fixed by the broadcast standard (NTSC, PAL, SECAM, or HDTV), so it does make sense to compare the resolutions of different TVs and different program sources. The higher the number, the better.

(Remember how horizontal resolution is measured: It’s the number of vertical lines across the biggest circle the screen can show, not the number all the way across the screen.)

Some TVs have more horizontal resolution than others (600H is very good; 800H or more is outstanding), but it’s hard as a shopper to compare numbers because often the number isn’t given and, when it is, they don’t say how it’s measured. Probably it makes sense to compare numbers within a given manufacturer’s catalog, under the assumption that, however it’s measured, it’s at least consistent. Fortunately, your choice of TVs will be determined mostly by other factors, and the problem of knowing the horizontal resolution when you’re comparing models will be less serious than it seems. And, as you would expect, HDTVs have higher horizontal resolutions than non-HD TVs, to go with their greater vertical resolution.

Horizontal Resolution of Program Sources

While it may be difficult to find out exactly what the horizontal resolution of a TV is, the horizontal resolution of given program source is generally fixed. It’s usually different from the TV’s resolution, but TVs can make the conversion automatically. (Ironically, expensive projection TVs are sometimes an exception— with them you use an external scaler, which you have to buy separately.)

Here are the horizontal and vertical resolutions of some typical sources:

From this table and what we already know about TVs, it’s apparent why DVDs look better than videotape, even on ordinary TVs: The horizontal resolution of the source is more than twice as good (500H vs. 240H), even though the vertical resolution (480V for NTSC) is the same.

Interlaced and Progressive Scanning

Given a certain number of horizontal lines on a TV screen, there are two methods that TVs use to display a picture on their screen. To explain these, look at Fig. 2-2, in which the horizontal lines (also called scan lines) are numbered. (Only the first 9 lines are shown.)

The first method is called interlaced. Line 1 is scanned, followed by line 3, and so on, skipping every even line. Then, scanning picks up with line 2, 4, and so on, this time skipping every odd line. Each scan from top to bottom is called a field, so only half the lines are scanned in each field. For NTSC, it takes 1/60 sec. to scan each field, and 1/30 sec. (or two fields) to scan all the lines and complete the frame.

The second method is called progressive. Here the lines are scanned in order, without skipping, so each field scans all the lines in 1/60 sec. A frame takes only one field. The picture looks sharper and clearer than does an interlaced picture, because we’re getting the full vertical resolution in each field, rather than half of it. Or, to say it another way, a full frame is shown every 1/60 sec. instead of 1/30 sec.

Progressive scanning is normal for computer screens, but until recently it hasn’t been used for TVs because:

·      NTSC, PAL, and SECAM are interlaced signals.

·      It’s more expensive to build a progressive-scan TV.

·      The first generation of DVD players produced only interlaced video, and HDTV didn’t exist, so there weren’t any progressive-scan sources.

But now the situation has improved: There are progressive-scan program sources available, and while progressive-scan TVs are still more expensive, at least they’re commonly available.

It’s useful to indicate whether a TV or a program source is interlaced or progressive by putting the letter “i” or “p” after the vertical-resolution number. Thus, NTSC and PAL/SECAM are 480iV and 576iV.

Now we get to the interesting stuff: DVDs are 480iV inherently, but there are ways to generate 480pV from them, which is what progressive-scan DVD players do (at extra cost).

The two new HDTV vertical resolutions mentioned earlier are 720pV and 1080iV, and nearly all HDTVs also provide a 480pV mode (sometimes called Extended-Definition TV, or EDTV), which works great with progressive-scan DVD players. Of course, HDTVs also handle the older TV resolutions (e.g., 480iV for NTSC).

(If you’re wondering about 720iV and 1080pV, which are logical variations on HDTV’s 720pV and 1080iV, they weren’t included in the HDTV specification because 1080pV was thought to be too much to ask of TVs, and 720iV is inferior to 720pV. Nonetheless, there are very expensive TVs that actually can handle 1080pV. They line-double the incoming 1080iV picture, as explained in the next section.)

We’ll have more to say about interlaced and progressive capabilities later in the book. For now, here’s what you need to remember:

·      Standard TVs are 480iV (NTSC) or 576iV (PAL/SECAM).

·      HDTVs in addition display 480pV, 720pV, and 1080iV.

·      For a given resolution, progressive scanning is twice as good as interlaced.

·      Even if you don’t care yet about HDTV, getting an HD-ready TV (an HDTV with just a standard tuner, rather than an HDTV tuner) is worthwhile for its 480pV capability, which is ideal for DVDs.

Note that in this section, all the numbers had a V after them, because interlaced vs. progressive is all about scan lines, which make up the vertical resolution. The horizontal resolution has nothing to do with interlaced vs. progressive.

Line Doubling

If a TV is capable of progressive scanning (i.e., has a 480pV mode), it can improve the picture from a 480iV source (e.g., broadcast TV, non-progressive-scan DVD) by including every line in both interlaced fields in each scan. All it needs to do is remember the lines from the previous field so they can be duplicated in the current field. This trick is called line doubling. For high-quality 480iV inputs, such as from a DVD player, line doubling makes a tremendous difference in picture quality, although it’s not as good as having a 480pV source to begin with. Fortunately, essentially all HDTVs do line-doubling.

(“Line doubling” is something of a misnomer, since you still have the same number of lines—they’re just displayed more frequently. Maybe “line duplicating” would be a more accurate term.)

Some TVs go even farther by doubling the horizontal resolution as well, or quadrupling the vertical resolution, or both. Some use very fancy processing, including even an analysis of image motion. Various spiffy marketing terms are used to describe the feature; for instance, Sony calls their advanced method “digital reality creation.”

For non-progressive DVD input, some TVs can do what’s called “3:2 pull down” instead of simple line doubling. This recreates the progressive-scan image from the interlaced input using a method more elaborate than simple line doubling. It’s almost the same as what a progressive-scan DVD player does, only it’s done in the TV rather than the player. The results are excellent, although it’s still usually better to derive the progressive-scan image in the player, rather than the TV.

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Standard and Widescreen Formats

Most TV screens are squarish, but movies are usually widescreen. By “squarish” I mean that, whatever the size of the screen, the ratio of its width to its height (the aspect ratio) is 4:3 or, to say it another way, 1.33:1. Therefore, a 30 inch (diagonal) 4:3 TV screen is 24 inches wide and 18 inches high.

Widescreen movies for theatrical release can be almost any shape, but the most common aspect ratios are 1.66:1, 1.85:1, and 2.35:1. Even some popular TV shows are now shot in widescreen, such as ER and The Sopranos. The different aspect ratios are shown in Fig. 2-3.

The aspect ratio 1.78:1 (16:9), shown in the middle of Fig. 2-3, is for widescreen TVs. It doesn’t exactly match any movie format, although it’s very close to 1.85:1. We’ll discuss widescreen TVs soon, after we talk about how widescreen pictures are shown on 4:3 TVs.

(Strictly speaking, a widescreen TV is not necessarily the same as an HDTV, but in practice nobody manufactures a standard-definition widescreen TVs. There are, however, a few 4:3 HDTVs, although most HDTVs are widescreen.)

Widescreen Images on 4:3 TVs

Since a widescreen image won’t naturally fit on a 4:3 TV, something has to be done to force it to the right shape. The reformatting is done when the source is created (e.g., reformatting a movie for showing on broadcast TV), or by the DVD player if it’s playing a widescreen DVD, or by the TV itself. Wherever it’s done, there are three methods for doing it, as shown in Fig. 2-4:

·      Pan-and-scan (P&S): Crop the image down to 4:3, discarding part of it. This has to be done carefully, as the part to be kept varies from shot to shot during the film.

·      Letterbox: Keep the whole widescreen image, but reduce it and put black bars at the top and bottom to fill a 4:3 rectangle. Sometimes called “matted.”

·      Anamorphic: Squeeze the image horizontally, keeping the height the same. Used on most widescreen DVDs. (The DVDs that aren’t anamorphic are letterboxed.)

Each method has its pros and cons:

For all three methods, the cons are worse for 2.35:1 widescreen than they are for 1.85:1. For instance, when a 1.85:1 widescreen image is letterboxed, about 25% of the scan lines are wasted on the black bars. For a 2.35:1 image, it’s about 40%.

Unfortunately, none of the three methods is entirely satisfactory. Ignorance is bliss: Most people who watch P&S movies on their 4:3 TVs probably never think much about what they’re missing, if they even know about it. But, as a reader of this book, you’re no longer ignorant. Sorry.

Sometimes the same movie is released on VHS or DVD in both widescreen and standard [4:3] formats, although, regrettably, most video-rental stores don’t stock the widescreen version. In the case of DVDs, sometimes both versions are on opposite sides of the same DVD. And, sometimes a movie is released only in one version. Do some research before you buy or rent so you know what’s available. More about this in Chap. 4.

Widescreen Images on 16:9 TVs

The best solution to the widescreen problem is to get a widescreen TV, one that’s 16:9 instead of 4:3. These TVs are designed for HDTV, which is inherently 16:9. (There are also 4:3 TVs that can show HDTV programs.) The ratio 16:9 works out to 1.78:1, so it’s almost right for 1.85:1 movies, too. And, while it isn’t perfect for 2.35:1 movies, it’s way ahead of 4:3.

There are four kinds of formats that widescreen TVs need to be able to handle, and so these TVs have four display modes, which are either automatic or settable with a remote-control button. The following table lists each mode and indicates what kind of input it’s used for. As you’re reading the table, refer to Fig. 2-4, where pan-and-scan, letterbox, and anamorphic images are illustrated.

Some TVs are pretty smart and can sense the format of the source and switch themselves into the best mode automatically, but more often you have to choose the mode yourself. What happens in practice is that you start watching, decide that the picture isn’t quite right (e.g., squeezed because it’s an anamorphic DVD, or letterboxed into a 4:3 area in the middle of the screen), and then operate the remote’s format button until you have things the way you want them. This sounds like more trouble than it really is, but after a while you get used to it and generally pick the right mode on the first try.

Here are some more comments about the table:

·      For 4:3 images with the TV in standard mode, since they fill the full height of the screen, you get the full 480V lines of vertical resolution. Part of the TV screen isn’t used at the sides, but that’s OK because the whole picture is still there. (That is, the whole picture as it came from the source is still there—if it’s a pan-and-scan picture, what’s gone is gone.)

·      For 1.85:1 letterboxed images with the TV in zoom mode, the TV screen is entirely full, so no TV screen space is lost at all. However, only about 75% of the vertical resolution is used; 25% was taken up by the black bars, even though they’re off-screen. Still, zoom mode looks pretty good, especially if there’s a line doubler. (Some high-end DVD players can zoom a letterboxed 4:3 image so the TV doesn’t have to; with these the TV sees a non-anamorphic letterboxed widescreen image as an anamorphic one, and no TV resolution is lost.)

·      For 2.35:1 letterboxed images with the TV in zoom mode, the images are treated as though they were 1.85:1, since the TV doesn’t know the difference. You still get bars at the top and bottom, but they’re much thinner than they would be on a 4:3 TV. (There aren’t any super-widescreen TVs in a 2.35:1 format.)

·      The previous point applies as well to 2.35:1 anamorphic images with the TV in anamorphic mode: You still get thin black bars at the top and bottom.

·      When the screen is filled with a 1.85:1 image, a very small sliver of the image is lost at the top and bottom, because the screen is actually only 1.78:1 (16:9), but this small error is hardly noticeable, and it’s a good tradeoff. The two cases in the table where this happens are 1.85:1 letterboxed images with the TV in zoom mode and 1.85:1 anamorphic images with the TV in anamorphic mode. It doesn’t happen with HDTV images, because HDTV is 1.78:1 (16:9), not 1.85:1 like movies. If a 1.85:1 movie is being broadcast in HDTV, the slight trimming is done by the broadcaster.

For images other than the main ones listed, such as 1.66:1 (e.g.,  Disney’s The Emperor’s New Groove), you treat them like 1.85:1 images, anamorphic or letterboxed, whichever is the case.

Here’s a pro-and-con table like the one in the previous section, only now revised to address the pros and cons of widescreen images on 16:9 TVs. The comments in the table are for 1.85:1 widescreen source images; as mentioned above, for 2.35:1 images the notation “fills screen” isn’t quite true, because there are still thin black bars at the top and bottom.

All this talk about thin and thick bars, across or at the sides, is probably a little confusing. Here’s a table to sort it all out visually:

Vertical Compression on 4:3 TVs

When I introduced the anamorphic image in Fig. 2-4, I said that it had been squeezed horizontally. To show it normally, I said a 16:9 TV had to stretch it back into its original shape. There’s another way to think of the image in Fig. 2-4: that it’s been stretched vertically, and the way to set it right is to squeeze it vertically. It turns out that some 4:3 TVs can actually do this, thus turning themselves into widescreen TVs.

I’ll call this feature “vertical-compression.” TV manufacturers also call it “v-compression,” “vertical squeeze,” “widescreen mode,” “squeeze mode,” or “16:9 mode.”

Vertical compression squeezes the image in a particularly clever way: by moving all the scan lines to the middle of the picture. There are still 480V lines (for NTSC, anyway), but they are closer together, so the part of the screen that’s actually scanned is 16:9, turning the TV into a widescreen TV with no loss of resolution.

The image on a TV in vertical compression mode looks exactly like a letterboxed widescreen image (as shown in Fig. 2-4), except that it looks better because of the higher resolution in the picture area.

Vertical compression only works with anamorphic images, which are found only on DVDs. It’s of no help with HDTV or with letterboxed widescreen images. Still, if DVDs are important to you and you want a 4:3 TV, this is a great feature to have, and it doesn’t add much to the cost of the set.

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Display Technologies

There are two basic kinds of TV displays:

·      Direct-view, which means that you’re looking directly at the image. Traditional TVs with picture tubes are direct view, but there are also thin-panel LCD and plasma direct-view TVs.

·      Projection, which means that you’re looking at a screen onto which a small picture is projected.

To understand how all the types work, it’s helpful to separate how a TV creates the image from how the image is displayed.

Image Creation

For HT, there are five ways for a TV to create an image:

1.        CRT (“cathode ray tube”), also know as a picture tube. This is the oldest and most common TV type.

2.        LCD (“liquid crystal display”), the same technology used on calculators, wristwatches, and portable computers.

3.        Plasma, used in high-quality, if expensive, thin-panel displays up to about 60”.

4.        DLP (“digital light processing”), used in projection TVs.

5.        D-ILA (“direct-drive image light amplifier”), also used in projection TVs.

In a CRT, the glass at the front is coated with phosphor and is illuminated by an electronic beam that goes side-to-side and up-and-down, tracing the scan lines. The resolution is controlled by electronics, so the same CRT can display different vertical and horizontal resolutions.

The other four technologies are called fixed-pixel displays, because there’s a separate picture element (“pixel”) for each picture dot, and hence the resolution is fixed. They don’t have the flexibility of a CRT with its electronic beam. If the source is at a different resolution, a circuit called a scaler has to modify it to match the display.

A plasma display also uses phosphor. Each pixel corresponds to a sealed cell containing gas that reacts with the phosphor to light up the cell. In a 480-by-852 color display, for example, there are 408,960 clusters of three cells each (red, green, and blue). Plasma displays are the most expensive and provide the best picture. A 50” plasma display costs around $15,000.

LCDs have a liquid crystal at each pixel (or three at each pixel, for color) that’s turned on or off by an electric current. Unlike the two phosphor-based technologies (CRT and plasma), an LCD doesn’t generate light. An external light source must reflect off it or pass through it.

DLP and D-ILA devices are very small, so they can’t be used for direct-view TVs, only for projectors.

The heart of a DLP device is the Digital Micromirror Device (DMD), an array, smaller than a postage stamp, of microscopic mirrors that move independently. A pixel is on if the light is directed to the lens, and off if it’s directed to the side. A beam of light passes through a spinning wheel containing red, blue, and green filters and is then reflected off of the DMD through a lens that’s focused on the screen.

D-ILA can be loosely thought of as a combination of LCD and DLP. The image is formed by bouncing light off of a reflective LCD. Sometimes D-ILA is called rLCD (“reflective LCD”) or LCOS (“liquid crystal on silicon”).

Image Display

There are three ways to display an image: direct-view, front projection, and rear projection.

In a direct-view TV, the image is created at the size you view it, and you look directly at the created image. Direct-view TVs can be CRT, LCD, or plasma. (DLPs and D-ILAs are much too small.) The problem for HT is that we usually want a large display; direct-view technologies get expensive when they get large. And, they’re limited in size at any price: CRTs and LCDs to about 40” and plasmas to about 60”.

A more practical way to get a big image is to create a small one and magnify it, just like projecting a 35mm slide with a slide projector.

With a front projector, it really is like showing slides. The projector is at the back of the room or up at the ceiling, and the screen is at the front.

Or, you can put the projector behind a translucent screen, which is how rear-projection works. To save space, a mirror is used to fold the light beam. Usually, the whole assembly is packaged into one large box containing the screen, the mirror, the projector, a TV tuner, an audio amplifier, and speakers. The whole business is called a rear-projection TV.

A projection TV can use four of the five image-creation technologies listed in the previous section (not plasma).

For front-projection, CRT-based projectors are the most mature and give the best pictures, but DLP-based projectors are now (Spring 2002) starting to appear and have created a new low-priced market ($3000 - $15,000). LCD-based front-projectors have been used for business presentations for years and a few models are designed for HT. There are also a few D-ILA-based front projectors.

For rear-projection, CRTs dominate by far, but DLP-based and LCD-based models are beginning to be introduced. They have several advantages over CRTs: shallower cabinets, sharper pictures, and less maintenance. Right now they’re more expensive, but that should change over the next few years.

Summary of Display Technologies

Here’s a table that summarizes how the five image-creation and three display technologies combine into the different TV types. In each column, the most expensive (and best, for right now) is marked with $ and the cheapest with ¢. “Yes” means products exist, and “no” means they don’t.

Some other points about the display technologies:

·      CRTs traditionally had curved screens, but now the better ones have flat screens, which makes it much easier to eliminate reflections.

·      Front-projection TVs require a pitch-black room, and the CRT-based ones require professional installation.

·      The LCD and plasma direct-view TVs are very thin and light, so you can hang them on the wall.

·      You get the most value for your money with a 4:3 CRT direct-view TV up to 36”, a CRT rear-projection TV from 40” to around 65”, and a DLP front-projector for really big images.

·      16:9 CRTs are expensive—consider a rear-projection TV instead if you have the space.

·      Phosphor displays—CRT and plasma—can be damaged by burn-in if the same image stays on the screen too long, or there are bars at the top and bottom or at the sides for too long. It’s very important that the contrast and brightness not be too high and that the images be varied from time to time. (This is why computers have screen savers.)

·      Front-projectors aren’t usually complete TVs. They all lack tuners (use a VCR or a set-top-box), and many lack scalers, which means you have to get a separate video processor. Make sure you plan out your whole system before buying so you don’t go over-budget. And don’t forget $1000 or so for the screen.

·      For a fixed-pixel display (anything other than CRT), the quality of the scaler is extremely important. Make sure you test a candidate system with the source you’re going to use it with (e.g., 480pV output from a progressive-scan DVD player). If the store doesn’t have exactly the right setup, you’ll have to hold the audition in your home.

·      Unlike direct-view and rear-projection TVs, with a front-projector you can get almost any size image you want, but the bigger it is, the dimmer. For the least-expensive front-projectors, a width of 80”-to-90” is about right. For a bigger room you’ll need a more powerful projector.

·      There’s a race on between LCD and DLP in the low-priced front-projector market. Quality is going up, and prices down. Great news, even if it makes shopping more difficult.

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Analog and Digital TVs

The words “analog” and “digital” as applied to TVs don’t mean much in and of themselves (not, say, like analog vs. digital clocks), but are rather catchall terms for how the TVs work internally and what resolutions they support. Sadly, a so-called digital TV still uses analog for its video input, so those wonderful digital sources (DVD, satellite, cable) have to be converted to analog before they go to the TV, even if it’s digital. This is true even of today’s HDTVs.

Practically speaking, then, analog means TVs that can handle a resolution of 480iV only, whereas digital means at least 480pV. To the extent that the term “HD-ready” means anything different from plain “digital,” it means that the TV can also handle the other two HDTV resolutions, 720pV and 1080iV. Furthermore, essentially all 16:9 TVs are digital.

Since no analog TV can handle the important 480pV resolution that’s so great for DVDs, for HT you should consider a digital TV if you can afford it.

Whether a TV is analog or digital, the input to it that you’ll most likely be using is analog. There is a new input type called DVI (“digital video interface”), which some high-end TVs have, but none of the common video sources (DVD, satellite, cable) use it yet. There’s more on this later on in this chapter in the section titled “Digital Video Input.”

TV Size

How Large a TV Do You Need?

Big 4:3 Instead of Smaller 16:9?

TV Inputs and Outputs

Physical Connectors

Analog Video Input

Digital Video Input

Audio Input

Summary: The Essential TV Inputs

TV Outputs

Useless TV Features?

Simplified Shopping

©2001, 2002 Marc J. Rochkind. All rights reserved. Send comments about this site to site@htexplained.com.