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Trying to wrap your head around something as outwardly simple as 'the difference between RGB and composite or S-video' shouldn't involve hours of research and dozens of diagrams and examples. It shouldn't involve research into human vision deficiencies, the history of TV, obscure photographic terminology or digital image technobabble either. And yet it does - all this and more.
So what exactly is RGB? Is it better than component video? How bad is composite video, anyway? Is S-video good enough? The answers to some of these questions are below. Some topics are glossed over a bit - like how we got here but you can find those answers on other pages (See contents on the right). I've already written several video format primers (like this one for GameGo Magazine) and you may recognize some of this content. Since those were written I've learned a lot more, and hope this new document will serve you better than the old ones. Note to PAL users:
This is an older image, but gives a bit of an idea of the differences in video formats. Consider component video to be more or less the same quality as RGB:
Click to enlarge
Part the first: Forgive me if I cover anything you already know, we're gonna start with the basics and work our way up. This is written specifically for game consoles, but the theory applies to many video devices like DVD players or computers. Your average game console isn't a lot different than your average computer, except that it's made as cheaply as possible by having everything not strictly necessary removed. If you took a standard desktop computer and chucked out everything not used for gaming, you might end up with something like this. It would contain a Central Processing Unit (CPU), some memory to work with (RAM), a Graphics Processing Unit, and a few other odds and ends to handle controller input, CD ROM access, etc. A simple, single-purpose computer.
After all the processing of game phyics, enemy AI, player response and whatnot is finished an image is digitally assembled in the video RAM, and then it needs to be converted into a signal your display can handle. Most video systems output an RGB signal, one that sends each colour along a separate wire and is almost as pure as the digital data. The exception is DVD players, which store the data as digital component video. Other devices like VCRs and LD players store their video in an analogue format, and suffer their own problems, so we're going to skip those for now.
Once the RGB signal is generated from the video RAM, it needs to be modified into something the average TV can use. Most of us have TVs that accept RF (cable) connections, or Audio + Video (AV) inputs. Some of us have a TV that accepts Svideo, and a few of us even have one of those new fangled TVs that accepts Component Video. RGB capable TVs are very uncommon outside of Europe, and are considered passe in Japan where they were once popular. We'll be looking at these formats in the above order.
First off, RF sucks. It's terrible, it's audio + video pounded violently into a single stream where it competes with all kinds of interference. The final result is completely unacceptable.
Remember those red, white and yellow cables you got with your video game system when you first bought it? They carry stereo audio (red + white) and composite video (yellow), and if you're not in Europe or some other small-time countries they're specifically using NTSC video. The NTSC standard is widely derided and is considered unacceptable for any post-consumer or professional use. It's a quagmire of oft-ignored standards and misleading specs, compounded by everything imaginable: The quality and age of your display, the quality of your cabling, operating temperature (Seriously!) and more. This is why other video formats are becoming more popular. It's the modern baseline, all new game systems and DVD players include AV cables not only because most TVs have AV inputs, but because they're the cheapest to make.
S-video uses two wires for the video instead of composite's single wire, and this results in a large drop in interference and an increase in colour purity and clarity. It also allows a 20-100% increase in colour resolution and near complete elimination of dot-crawl. It's far better than composite video and most new, larger TVs support Svideo inputs.
Component video isn't a new format, but it's quite new in consumer electronics, becoming popular with the first DVD players. It's generated with a mathematically complex formula that takes a video signal and divides it into three parts: A black + white Luminance (brightness, Y) signal and two Chroma (colour Y-r + Y-b) channels. The television receiving these signals recombines the three signals into a coherent whole for display, subtracting the blue and red from the brightness signal. Whatever's left over is green, the end result is a high-resolution green channel and a low res red + blue channel. There's a certain amount of quality loss with this method, especially when the signal comes from a DVD source where the red + blue signals are typically 75% lower resolution than the green. Please see the page on human vision deficiencies for reasons why this isn't as bad as it sounds. While there's no maximum spec for component video in terms of resolution, the limited bandwidth for the two colour channels means that you cannot easily achieve the same kind of colour vibrancy RGB offers - but it's still better than any non-RGB format.
RGB is the king of all video formats, with no maximum resolution beyond the abilities of the display generator + receiver used. It's no more wiring intensive than component video, with only three wires needed. Historically though RGB was unecessary except for computer displays, so it never made inroads into consumer hardware and there's no standard connector. Combine this lack of standardization with the movie industry's unwavering belief that we're all pirate scum and you end up with a lack of interest in this pure format. Since Macrovision's pathetic 'copy protection' cannot be easily applied to RGB component video is the format of choice. Outside of Europe only studio-level and some progressive DVD players offer RGB output. Sony's PS2 unit goes so far as to disable the RGB output when playing DVDs, requiring a cable swap when changing from movie-watching to game-playing and depriving millions of an easy solution to image clarity woes. All this effort even in the face of sub-$20 macrovision defeating devices!
For the time being component video, with its low resolution colour and easily defeated 'protection' (Note: Screw you, Macrovision) is likely to remain the format of choice. The fact is most of us think DVDs are great, and for many of us that's as good as we need for now. For the purists and the diehards (and the crazy), RGB is the best stuff around.
Please see this page on colour resolution for some more technical discussion on the different formats, including more pictures and proof that Svideo really is better than composite!
Chroma Compression in JPGs - Rick Matthews
Understanding Human Vision (dead link) - Clairvoyante Labs
Video Signal Formats (dead link) - CyberTheater.com
Video/TV/Computer Topics (dead link) - Allan W. Jayne, Jr.
DVD Chroma Upsampling Bug - hometheaterhifi.com
In this series:
Video Colour Resolution
Human Vision Issues
Brief History of TVs
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