Now, the frame rates quoted for both PAL and NTSC don’t really tell the whole story, because in reality a PAL image is drawn 50 times a second, while an NTSC image is drawn 60 times a second. The reason for this is that each full frame takes two scans – the television will draw the even and odd numbered lines on separate passes to create a solid image. This is known as an interlaced image. Of course this happens so fast that it should be indistinguishable to the human eye, but that depends entirely on the content being displayed. Problems can occur when there is very fast movement being displayed as this can result in the two halves of a frame not lining up perfectly and thus looking somewhat blurred.

As if the inherent problems with interlaced moving images wasn’t enough, there is another big issue that has historically afflicted our television systems. While PAL runs at 25fps and NTSC runs at 30fps, actual movies are shot at 24fps. Obviously for PAL the difference is pretty minimal and the traditional solution was to simply speed the film up by around four per cent, thus creating a 25fps frame rate. The downside of this method is that the pitch of dialogue and music rises as a result.

The pitch increase when transferring film to PAL video can be avoided by using a different, although more complex method. The original film can be transferred on a one-to-one basis to PAL video, but every twelfth frame is repeated, thus creating 25fps, rather than the original 24fps, without the need to speed up the playback.

Transferring film to NTSC video is far more complex and involves a somewhat infamous technique called 3:2 pull down. This process is far more complex than either of the PAL solutions and I don’t have the time (or inclination) to explain it fully here. However, it is fair to say that the processing involved in the 3:2 pull down method results in degraded image quality compared to the original footage, with smooth camera pans often appearing jerky when watched as NTSC video. In its favour though, it doesn’t result in the increased audio pitch seen with the traditional PAL transfer method.

So, traditional standard definition television systems rely on an interlaced image creation, where each complete image is drawn in two passes – this coincided with the way a cathode ray tube television worked. The maximum amount of resolution on offer is 576 lines using PAL and only 480 lines using NTSC, and the frame rate can be either 25fps (50Hz) or 30fps (60Hz). But just how much does high definition TV improve on this?

1) The minimum resolution of the display must be 720 lines in a widescreen aspect ratio.
2) The display must accept an HD signal via an analogue YPbPr (component video) connection and either DVI or HDMI digital connections.
3) The HD inputs must accept both the standard high definition formats:
• 1,280 x 720 @ 50 & 60Hz Progressive (720p)
• 1,920 x 1,080 @ 50 & 60Hz Interlaced (1080i)
4) The DVI or HDMI digital input must be HDCP compliant.

It’s worth pointing out though, that the HD Ready logo requires a widescreen aspect ratio and NOT a widescreen resolution. This is why certain plasma TVs carry the HD Ready logo, but bizarrely sport what looks like a 4:3 resolution like 1,024 x 768. Despite the physical resolution, these TVs still produce a widescreen aspect ratio due to the way the pixels are constructed or laid out on the glass.

Number two is pretty self explanatory. The stipulation for component video and a digital input is a good decision, giving the consumer the option of connecting pretty much any high definition source to the TV. I was very happy to see that component video was a prerequisite, since I have spent many years arguing with people who believed that SCART RGB was better quality than component video, and the fact that it is part of the high definition standard kind of proves my point.

Number three is interesting because, as mentioned before, the devil is in the detail. The thing to remember here is that an HD Ready television only has to accept both 720p and 1080i signals, but it doesn’t have to be able to display the 1080 lines of information for the latter format. This means that if your HDTV has a resolution of 1,366 x 768, it will downscale the 1080 signal to 720 lines and display it, since it physically doesn’t have enough lines. I’ll come back to resolutions and standards in a minute, but for the moment let me finish explaining the HD Ready requirements.

Number four stipulates that the digital interface must be HDCP (High-Bandwidth Digital Content Protection) compliant. Again I’ll go into more detail about HDCP a bit later, but ensuring that a TV has this feature means that any copy protected source material can be displayed without issue.

With this in mind, there’s a fair amount of debate over which gives better image quality, 720p or 1080i – the argument being that even though 720p has fewer lines, the fact that they are delivered as a whole frame potentially makes for a better image. However there is one very important factor that discounts that argument – both LCD and plasma panels are progressive by default. In fact since the vast, and I mean vast majority (in Europe at least) of high definition TVs are either LCD or plasma based, you can’t help but get a progressive picture.

Let me elaborate on this a little. As already mentioned, a CRT television draws an image in two passes by scanning from the top left corner of the screen to the bottom right, but both LCD and plasma TVs are fixed pixel devices, so there is no scanning involved. This means that even if you wanted your LCD or plasma high definition TV to display an interlaced image, it couldn’t.

What about if you feed it a 1080i signal? That’s a good question, but one that’s easily answered. If you pump a 1080i signal into an LCD or plasma TV, the television de-interlaces the signal before displaying it on the panel. So, even though the signal being fed to the TV is interlaced, the actual footage displayed on the panel will be progressive. Therefore a 1,920 x 1,080 panel showing 1080i content should look superior to a 1,366 x 768 panel showing 720p content, while pumping a 720p signal to a 1,920 x 1,080 panel should also look less impressive than when that same screen displays 1080i content.

Now, before all those readers who have bought 1,366 x 768 HDTVs start to cry, there’s more to a great high definition picture than resolution alone. Some of the best quality high definition pictures right now can be seen on TVs with only 768 lines, because the image processing in those sets is so good. In fact it’s worth remembering that you could look at two HDTVs from different manufacturers but using the same panel, and the resulting pictures could be entirely different due to the proprietary image processing that each manufacturer implements.

One thing’s for sure though, traditionally an HDTV with a 1,920 x 1,080 panel would cost you significantly more than a similarly sized 1,366 x 768 model. But that changed recently with the launch of the Toshiba Regza 42WLT66, which offered a Full HD 1,920 x 1,080 panel at a stunning price point. Let’s hope that this is a sign of things to come.

There’s a lot of talk going round at the moment about 1080p compatibility and the fact that current TVs don’t support this standard. It’s true that current HDTVs can’t support a 1080p input, but this really shouldn’t be anything to worry about. As I mentioned in the last page, if you feed an LCD or plasma TV a 1080i signal, it will de-interlace that signal and present you with what is essentially a 1080p picture.

Theoretically, de-interlaced 1080i footage should look identical to native 1080p footage as long as no post processing steps are applied during the original conversion process that could degrade the quality. It’s also worth remembering that even movies that are shot digitally in a 1080p 24fps format will need to undergo some conversion to meet the 25fps PAL standard or the 30fps NTSC standard.

Ultimately though, as more and more movies are shot digitally in 1080p (Star Wars Episode III: Revenge of the Sith was shot in 1080p24), the demand for source devices that output 1080p and HDTVs that accept 1080p natively will grow. Whether this should sway your buying decision now is debatable, but ultimately it depends on how long you're willing to sit on the fence.

I’m not going to go into excessive detail here about HD DVD and Blu-ray since I’ll be covering this in a separate feature, but I will touch on the basics. The basis of both these formats is that they offer high enough capacity to store high definition media. Whereas a standard DVD disc can store 4.7GB per layer, an HD DVD can store 15GB, while Blu-ray can manage a whopping 25GB. It’s this extra capacity that the Blu-ray consortium will cite as a clear superiority for the format, especially since Sony has already achieved eight layer engineering sample discs with a capacity of 200GB! The current theoretical limit on HD DVD is three layer, offering a maximum of 45GB per side, which is still 5GB short of the Blu-ray dual layer capacity.

It’s worth remembering though that the next generation of optical storage will have two uses, just like the previous two generations. The first use, as already mentioned, is as an entertainment distribution medium, but the other is as a data storage medium. The computer industry has always made use of optical media for storing and distributing data, and that’s exactly what’s going to happen with Blu-ray and HD DVD. In fact I’ve recently reviewed a Sony notebook - the VAIO VGN-AR11S - with an integrated Blu-ray drive, and believe me, that’s just the tip of the iceberg. But here’s where things get a little complicated. Obviously for data storage, the higher capacity the better, which puts Blu-ray in the driving seat right? Well you’d think so, but with both Intel and Microsoft backing HD DVD, it’s not going to be that simple.

The answer to every consumer’s dream would be a drive/recorder that can use both formats, but although there has been much talk around this subject, nothing has been officially agreed yet. However, the good news is that Ricoh has recently announced a laser technology that will read both formats, which is a definite step in the right direction. But I really don’t think that it’s technology that’s standing in the way of unified hardware, more the millions of pounds spent on marketing each format.

You can expect to see lots of Blu-ray and HD DVD hardware start to appear over the coming months. It will no doubt be very expensive, and the chances are that the early adopters will carry the burden while manufacturers try to claw back some of their R&D costs.

HDMI or High Definition Multimedia Interface represents the natural progression for AV equipment. In the PC industry the switch to a digital interface between computer and monitor happened a long time ago when LCD panels became prevalent. However, the ongoing use of CRT for televisions meant that a digital to digital link between source and display was not possible, but now that LCD and plasma screens have become the norm, a digital link is the obvious choice.

HDMI is very similar to DVI except that it can carry digital audio as well as video. You may well find early HDTVs with a DVI port instead of an HDMI port – this won’t be a problem as converters are easy to come by, but you will need to connect the audio separately. HDMI can carry up to eight channels of uncompressed digital audio, but to make use of that multi-channel goodness you’ll have to be sending the signal to a surround sound amplifier. That said, if you’re serious about your home cinema you’ll want to hook all your source devices to an amp, and then run a single monitor cable to your TV.

Another advantage that HDMI has over DVI is the size of the connector. An HDMI connector is tiny compared to DVI and it also just plugs straight in rather than having screws on either side. Also it can be all too easy to bend the pins inside a DVI plug whereas an HDMI plug is far more robust.

An HDMI port is only half the story though, both your source device and your TV must be HDCP (High-bandwidth Digital Content Protection) compatible. HDCP is Hollywood’s safeguard against high definition piracy. With a digital interface like HDMI, the last thing that Hollywood studios want is for you to be able to make perfect digital copies of its high definition movies. HDCP stops digital copies from being made by encrypting the data stream that travels between source and display, and making sure that both devices are allowed to talk to each other.

Both Blu-ray and HD DVD players will have Ethernet ports, which allow the player to communicate with the manufacturer and movie studios. Software can demand that a player is online before the movie is played and if the studio recognises the player as being compromised as far as copy protection goes, it can revoke the player’s licence to play the content. The subject of your movie player constantly communicating with third parties and logging your viewing habits is somewhat concerning and something that I will cover in greater depth in my future Blu-ray and HD DVD feature.

If an HDCP enabled source device recognises that the display it’s connected to isn’t HDCP compliant it may choose to either downgrade the resolution of the video (thus negating the point of HD) or even not show the video at all. Thankfully it’s pretty hard to find an HDTV that isn’t HDCP compatible these days.

Just to confuse matters, the HDMI 1.3 standard was recently announced and should be appearing on devices towards the end of the year. The new standard significantly increases the available bandwidth, thus enabling more detail (both visually and audibly) to be sent down the cable. Does this mean that you shouldn’t buy any equipment that’s using the current HDMI 1.1 standard? Probably not – one thing I’ve learned from working in the technology industry for so long is that there is always something better coming down the line, but you can’t sit on the fence forever.

If your TV doesn’t have an HDMI port, you can still watch high definition content via a component video input. Component video is widely regarded as the highest quality consumer analogue video connection. Component video separates the video signal into three parts, luminance (light), blue chrominance (blue colour) and red chrominance (red colour). These three parts are often referred to as Y, Pb and Pr. The three parts of the video signal are transported discretely along the separate cables to ensure the highest possible quality. There is no need to transport a green signal since anything that isn’t blue or red is assumed to be green.

Although HDMI has an overriding advantage of keeping the signal digital from start to finish, a high quality source connected to a high quality screen using a good component video cable will probably be indistinguishable from an HDMI connected setup to most people.

One final connection worth mentioning is UDI or Universal Display Interface. As if DVI and HDMI weren’t similar enough, UDI has now been thrown into the mix. UDI is being touted as the replacement for the analogue D-SUB port used on graphics cards and computer monitors. Although I can’t help but think that DVI was the replacement for D-SUB.

Despite the fact that UDI seems to offer no great benefit over DVI and HDMI for consumers, manufacturers would benefit – to use HDMI a manufacturer must pay an annual licence fee and royalties on every unit produced.

Just getting up and running with Sky HD is going to set you back £299, because that’s how much you’re going to have to pay for the box. The Sky HD box is manufactured by Thomson, a company with a pretty decent heritage when it comes to AV equipment. The box definitely looks good, finished in black and silver, and should complement your current AV line up.

Like all Sky Digital boxes, the Sky HD box is supposed to be connected to your phone line at all times so that it can receive updates from Sky HQ. I have to say that I’m very surprised that Sky doesn’t allow its boxes to communicate over the Internet instead, since so many households have broadband these days. That said, the inclusion of an Ethernet port at the rear points to Sky adopting this method in the near future, especially since the company is now touting its own broadband service.

The Sky HD box has Sky+ functionality built into it, so you can pause live TV, rewind something that you may have missed, or schedule recordings of an entire series so you never miss an episode. There’s 160GB of hard disk space to facilitate recording, but the installation engineer told me that there is almost that much space again but Sky hasn't made it accessible to the customer.

But once you’ve got past the cost, once the wait for installation is over and you sit down on your sofa and fire up some HD content, it somehow all seems worth it. Seriously, once you’ve watched an episode of the BBC’s superb Planet Earth nature programme, you’ll never want to watch standard definition again – which is a shame considering you’ve just signed up to hundreds of SD channels as well as the handful of HD ones.

The Sky HD box does give you the option of copying recorded content to a VCR or DVD recorder, but before you get too excited, any high definition recordings are downgraded to standard definition before the copy process starts.

If there’s one problem with the Sky HD service, it’s that there aren’t enough high definition channels, but I’m sure that this will change over the coming months. But even as it stands I’d say that the service is worth the money, just so that you can get the best from your shiny new HDTV.

If you previously fell into either of the above categories, hopefully this feature has helped you gain a better understanding of the high definition revolution. I know that the situation is confusing, but if you have a basic understanding and choose your components wisely, you’re in for a real viewing treat.