Making sense of 1080p

Freesat is a new, free (obviously) digital satellite television service launched as a not-for-profit joint venture by the BBC and ITV. Up to 200 channels are expected to be available by the end of the year. The BBC HD high-definition channel is available at launch. ITV HD will be offered as a red button service exclusively on Freesat.

On the day that Freesat (the new one, not the four year old Sky one) launched, 6 May 2008, the new platform's commercial director was asked about the HD content of the new free-to-air satellite service.

He told What Hi Fi: 'Whether you'll see 720p or 1080i will be largely up to the broadcasters. We're trying to maintain the native content of the content wherever possible. The boxes will include their own upscalers - the Humax, for example, comes shipped as 1080i.'

The general public

It occurred to me that my old man wouldn't know what the commercial director was talking about. So I asked him (my dad that is). He didn't know. Neither did my brother. Or my geeky video-games-playing friend. Or my slightly hippy-ish cousin.

In fact, very few people I know outside of work would know the difference between 1080i, 1080p and 720p - which is a bit odd seeing as though they are the target audience for Freesat and HD television sets. They don't know that they'll need a new set-top box for HD on Freeview. And they don't know the difference between a 720p TV and a 1080p TV.

This is partly because the technology is new. And partly because it is very confusing. But, I reckon there are people who work in television who also don't understand. So, to save any further embarrassment, this is what I told my dad.

• Most HD broadcasts here in the UK are done in either 720p or 1080i.

• The number (720 or 1080) is the number of horizontal lines that make up the image. The letter (i or p) denotes how the signal is scanned.

• Hence, 720p has a resolution of 1280 pixels x 720 lines. It is displayed progressively (p). By that I mean that each line of the picture is displayed on the screen simultaneously. This makes the image smooth.

• 1080i has a resolution of 1920 pixels by 1080 horizontal lines. 1080i is ‘painted' on the screen in two interlaced (i) halves. First, all 540 even-numbered lines are ‘painted' on the screen. Then the odd-numbered lines follow. These two fields together form a single frame of 1080 lines. The picture is more detailed than 720p but is not as smooth.

• Your current telly broadcast pictures are interlaced. This is done to save on bandwidth. CRT (Cathode Ray Tube) TVs show these two images very quickly one after the other so you cannot see the join. Plasmas and LCD screens don't work in the same way - they work progressively.

• Then there is 1080p, which is better still than 720p and 1080i as it has the full 2.07 million pixels (1920 x 1080) but also displays everything in one smooth progressive go. But at the moment the only HD content available in 1080p is Blu-ray and HD DVD discs.

How does that affect LCD or flat screen monitors?

Ian Morris, television editor at CN Net describes this better than I do so I'll leave it to him.

He says: “The fact that flat panels don't use interlacing means that there is no such thing as a 1080i LCD or plasma. Instead, these screens will offer a native resolution of either 720p or 1080p. If a flat-screen TV is touted as 1080i, it really just means it's a 720p TV that converts a 1,080 line interlaced signal into a progressively scanned 720 line one. To have the 'HD Ready' label, all TVs must support 720p and accept input signals of 1080i.

So, having described them, which is the best?

Looking at the numbers you'd say that 1080i is better as it has more than two million pixels while 720p has just under a million. But interlaced images have their limitations, making the difference barely even recognisable. And, to be honest, 720p is better for fast moving scenes in movies or sport as it has less flicker. And 1080p is better quality than both but no one is transmitting in that format at the moment, it is just for DVDs and games.

I hope that helps clears things up. If not, here are some other sources to try:

1080i and HDTV resolution explained

HDTV explained

What is Sky HD (PDF)

If you're thinking this variation and incompatibility could cause trouble, you might be right.

Just days before the Freesat launch, there was talk of one day seeing 1080p broadcasts (contradicting nicely what I've just told you). Tandberg TV chief exec Eric Cooney predicted that satellite TV services will introduce 1080p HD programming within three years.

So, what does this mean for people on the frontline?

If you're buying a TV, get one that does 720p and 1080i unless you play a lot of video games and are dead set on Blu-Ray and you only want to buy one TV in the next ten years. In that case, plump for one that can handle 1080p.

If you are shooting pictures or making programmes and are looking to future proof your supposedly future proofed HD content (!) then maybe acquiring in 1080p is not such a bad idea.

Because what happens if the broadcasters DO decide they want to broadcast in 1080p because consumers DO have 1080p TVs and the equipment manufactures DO want it to happen and bandwidth technologies DO sufficiently improve? Well, we'd be back to the start and I'll be explaining acronyms and numbers to members of my extended family all over again.

Have you got an opinion on HD formats? Has Will has got it wrong? Have your say below.