1. HDTV Is Here

We've been waiting over a decade for HDTV, and now that it's finally available, there's as much confusion in the marketing as there is clarity in the images. If you're won over by the promise that your favorite films and sports will wow you all over again, and you buy a new TV with an HD-ready sticker on it for Christmas, how much more will you need before you actually see an HD image on the screen? Here's the current state of the game.

HD Basics

HD stands for high definition; a higher resolution than the 'standard' TV pictures we're used to. It doesn't have to be broadcast in digital format but usually is, in part because that allows the large picture to be compressed for broadcast; HDTV uses either MPEG2 or MPEG4.

Confusingly, HD covers a range of resolutions; currently an image can have 720 or 1080 vertical lines in 16:9 widescreen format, resulting in pixel resolutions of 1280x720 and 1920x1080. Unlike standard TV, pixels aren't being stretched to fit the 16:9 image. You won't see letterboxing, except on extra-wide movies like Lord of the Rings; if you're watching HD content that's been produced in the older 4:3 aspect ratio you'll get black bars on the side instead.

HD also covers both interlaced images - the system used in CRT screens to paint alternate lines of the image - and progressive scan, the system used by LCD and plasma flat-screen TVs. Most HD content is produced as interlaced, and there is some discussion over the quality difference between 1080 interlaced (1080i) and 1080 progressive (1080p). This is complicated by the fact that interlaced content has to be de-interlaced for display on a progressive screen, which degrades the image. in fact, 720p content may look better than de-interlaced 1080i on a progressive screen, though unless you have a large screen and good content to start with you may not see much difference anyway. 1080p content would certainly look better, but this takes a lot of bandwidth to broadcast and won't be available any time soon. Blu-Ray discs will generate 1080p images, as will a PlayStation 3 (although the content may be scaled up by a factor of four so don't expect fantastic quality for everything from a PS3). Xbox 360 produces 1080i output, as does the first generation of HD-DVD, though future players will support 1080p.

Standard television may look better when it's de-interlaced on a progressive HD screen because motion may look smoother, but poor-quality images will be more noticeable too. Normal DVD content is of good enough quality that it looks better on an HD screen, especially if the DVD player has its own progressive scan processor.

HD content tends to have 5.1 channel Dolby Digital AC-3 surround sound, rather than the stereo sound of standard TV.

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