So what is "Component Video" anyway?
by Evan Powell, ProjectorCentral, February 26, 2001
http://www.projectorcentral.com


If you are just getting into home theater you will no doubt be confused by a lot of the jargon. And since the term component video is sure to befuddle just about everyone, here's a little primer on the subject. It might sound a little technical at first, but if you've got a DVD player, read on for some important information.

Starting at the beginning: RGB

Believe it or not, your eyes can see only three colors—red, green, and blue. All of the other colors and shades of the spectrum you perceive are the result of your brain interpreting the mix of red, green, and blue signals coming from your eyes. Pigments of your imagination, you might call them. (Sorry.)

Therefore, since your eyes only see red, green, and blue, a video system needs to capture and reproduce only red, green, and blue, or RGB as it's called. The camera must capture RGB on the front end. That information must be delivered accurately to your television or projector which must display RGB. By varying the intensity of red, green, and blue, every color of the spectrum can be reproduced. Voila. Perfectly natural color on your screen.

A Problem: Bandwidth

So how do you transport an image from the camera to your TV or projector? You could transmit it in the RGB format in which the camera first captured it. However, RGB is a bandwidth hog and bandwidth is expensive. So the first thing that happens is RGB is converted into a more compact format. This format is component video.

Component video consists of three signals. The first is the luminance signal, which indicates brightness or black & white information that is contained in the original RGB signal. It is referred to as the "Y" component. The second and third signals are called "color difference" signals which indicate how much blue and red there is relative to luminance. The blue component is "B-Y" and the red component is "R-Y". The color difference signals are mathematical derivatives of the RGB signal.

Green doesn't need to be transmitted as a separate signal since it can be inferred from the "Y, B-Y, R-Y" combination. The display device knows how bright the image is from the Y component, and since it knows how much is blue and red, it figures the rest must be green so it fills it in.

Once we've got our video information packaged up in component video format we've reduced bandwidth requirements by a factor of 3 to 2. But more compression was required for broadcast purposes. So back in 1953 when color television was born, a technique was developed to compress all of the component video information into one signal for broadcast. That one signal defined by the National Television Standards Committee (NTSC) is known as composite video.

Composite video shows up everywhere these days. It is (except for HDTV) what comes over the air to your TV's antenna, or through the coaxial cable from your cable TV provider. The yellow "video" jacks on the back of your VCR, laserdisc player or DVD player all output composite video.

The good news is that it only takes one wire to carry a composite video signal. The bad news is that the display system, whether it's a television or projector, needs to un-compress the composite signal, restore it to its original three-signal component video format, and then derive from that the RGB information for final display.

The problem is that picture information is lost when component video is compressed into composite format. Furthermore, once you pack luminance (Y) and chrominance (C) information into one signal, it cannot ever be separated cleanly again. So when the television or projector tries to convert the composite signal back to component video, it can't recover the entire original signal. The result is that the final video image on the screen is diminished—the picture is not as crisp and clean, and the colors aren't as accurate and rich as they would have been had the composite video compression been avoided.

So what does all this mean to you?

If you want good picture quality, there's some amazingly good news here. The news is this: DVDs are encoded in component video!. This is a big step forward since VHS tapes and laserdiscs are encoded in composite video. So the signal information in those media is already diminished and compromised. But DVD is a different animal—not only is it more compact and easy to use, but a much higher quality format is on the DVD itself. All you need to do is take advantage of it.

To do that, you need a DVD player with component video output, and a television or projector with component video input. You can connect the two with a three-wire component video cable. When you do this, you transfer the high quality signal from the DVD straight into your display system without it ever being converted to composite video. The result—better detail, a cleaner picture, and more accurate and richer color.

But wait, there's more. Let's say you are one of the vast majority of consumers out there whose DVD player doesn't have component video outputs or your television or projector doesn't take component video input. What you then have is two connection options.

First, you can do what most people do--use the simple yellow (RCA) video jacks. Actually this cable is often bound together with the audio connectors to make it even easier—yellow for video and red and white for audio. Couldn't be easier, right? Big mistake.

The second connection option (the better option) is that you can use the clumsy 4-pin S-video jacks. This often requires a trip to the electronics store to get a more expensive cable. Most people don't want to bother. So they use the yellow RCA jacks because they are labeled VIDEO, and because that's the cable that came with the DVD player. Once they hook it up and turn it on, they find that the picture looks better than their VCR. So they are happy and forget about S-video. This is of course the wrong thing to do.

Why? Because by using the yellow RCA video jacks, you are forcing your DVD player to down-convert all that great component video information on the DVD to lowly composite video in order to transmit it to your television or projector. You lose much of the picture quality that the DVD can deliver by doing this. OK, it looks better than your VCR. But you aren't getting the best picture you can get.

So the alternative, S-video, is a MUCH better solution. An S-video cable actually carries two separate signals, one for luminance (Y) and one for chrominance or color (C). The Y signal is the same as in the native component video format. And the C is simply a combination of the B-Y and R-Y color difference signals. (Sometimes you will see S-video referred to as Y/C.) By keeping luminance and chrominance information separate on two wires it prevents most of the signal degradation that is inherent in the conversion to single-wire composite video.

So. If you've got a DVD player and want to give yourself an instant video system upgrade, replace the composite video RCA cable (the one with the yellow plugs) with an S-video cable (round connector with four little pins). It's simple and inexpensive, and you will get a much better picture.

Use component video if you have it

If you have component video output on your DVD player and your TV or projector can take that signal, use it. DVD players with this output usually have three RCA jacks which are color-coded green, blue, and red. They are labeled either Y, B-Y, R-Y, or alternatively Y, Pb, Pr, or Y, Cb, Cr. For practical purposes they are all the same thing. If your television or projector also has the same three RCA jacks, just connect them with a three-wire component video cable making sure the colors match up on both ends (or you can use three standard composite video cables to do the same thing).

Frequently a projector will take component video, but only through a VGA port, commonly a 15-pin D-sub like the output ports on a PC. In this case you will need a cable that has the three RCA jacks on one end for the DVD player, and a 15-pin D-sub VGA connector on the other. You can order this cable from most projector manufacturers that market projectors with this interface.

Progressive vs. interlaced component video

We've got one more important thing to cover on this topic. Component video comes in two flavors—progressive and interlaced.

There are three basic kinds of DVD players. First, there are those that have composite and S-video outputs only. Second, there are those that have composite, S-video, and component video interlaced (480i) outputs. Finally, there are those that have composite, S-video, and two forms of component video—component interlaced (480i) and component progressive (480p) outputs.

People often make a big mistake these days by going out to buy a DVD player knowing that "component video" is an important thing, but not being aware that there are lots of DVD players that output "component-interlaced only" and not component-progressive. Both products will say they are "component video" compatible, but if you don't know the difference, you can end up buying something you don't want. If your current video display system takes component-progressive 480p (or you intend to get one that does), you will need to make sure your DVD player offers this as an output as well.

It is important to know this when buying a projector or TV also. There are projectors on the market that will take component-interlaced 480i, but not component-progressive 480p. Some with take both, and some will take neither. The best picture quality will often come from matching a DVD player with a projector that both have component progressive 480p.

If a projector specification sheet says that it takes component video, DO NOT assume that it takes both 480i and 480p unless it specifically states that it is 480p or component-progressive compatible. Sometimes a specification sheet will state component video compatibility, but it means 480i only.

(NOTE: At this writing, if the line item "Component video" on our Projector Database specification sheets says "yes" it means that the projector will take either 480i or 480p but not necessarily both. We are presently in the process of upgrading our Database to include specific indications as to compatibility with component 480i and 480p individually in order to eliminate this confusion. But until that is done, be aware of the issue if you are currently buying a projector or large screen TV for your home theater.)

Conclusion
The way to get the best DVD picture is to use component video connections (if you have them) between your DVD player and your TV or projector. Component-progressive is preferred when you have both progressive and interlaced options.

For the vast majority of DVD users who don't have component capability in either their players or their display systems, the next best thing is S-video. If you are one of the large majority of DVD enthusiasts who are running composite video out of your DVD player and inadvertently degrading the picture as a result, give yourself a quality upgrade--get an S-video cable as soon as possible.

Summary of Video Quality:
HIGHER < Component Progressive / Component Interlaced / S-Video / Composite > LOWER