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When I set out to write this article I discovered that there was much to learn about this subject. And some stuff weren’t all that easy to understand either. I am going to do my best to simplify the topic as best I can.

Now days with the introduction of Plasma, LCD and LED monitors and TV’s have become easier to handle, even if you should buy a 50″ screen. However; new technology also bring new standards. New equipment means new cables, new standards, like HDMI, and DV-I. Meaning you really have to know if your “old” equipment is compatible with your new. To really add to the confusion, you see tags like HD-Ready, Real HD, 1080p and so on.

Have you wondered what these tags mean, or if it’s something you really need to pay attention to ?

In the not to far away past, buying a TV or a Computer monitor boiled down to the size of the thing. The larger screen you wanted, the larger desk space you needed. It was easy. If you were especially interested you could get a TV with 100HZ display and get a Flat Screen (without the traditional curve). But the TV (or monitor) was still massive, heavy and required lots of available space. Due to the use of CRT or Vacuum Tube technology. Back then, you could rely on the fact that the new screen would “talk” with your old equipment – a set industry standard.

What is HD, and what’s the difference between the 720p, 1080i and 1080p ?

HD is short for High Definition, meaning you get better image quality than before. The numbers 720, and 1080 is supposed to show you exactly how much more information you should expect your new screen to display. And the higher number you get, the better, right ? Or is it ?

Before we can get into that, we need to know a bit about how TV’s and monitors work.

Lines

All images are divided into a number of lines to be drawn on your screen. The numbers 720 and 1080 represents how many lines (downwards) the screen can produce. The first TV broadcasts (back in 1920) used 240 lines, but the normal standard became 480.

Progressive and Interlaced (‘p’ and ‘i’)

I am going to over-simplify things here, but traditionally, Computer Screens (also known as CRT – cathode ray tube) use Progressive signals, and your old Vacuum Tube TV use Interlaced Signals.

Interlaced Scan

This is where we get a bit confusing. As you know TV and Movies are nothing more than thousands of still-images displayed in a very short amount of time. Fooling our eyes to believe there is motion. Back when TV signals were invented, one of the big problems was bandwidth. The lower bandwidth you need, the quicker and cheaper the transmission will be. So what they did was to invent a way of sending two different images at once. Called Interlacing.

What you see is two images on top of each other displayed with 1/60th (NTSC) or 1/50th (PAL) of a second a part. On new HD-monitors you can sometimes see these lines in interlaced scans when moving objects move too fast for the technology to transmit enough frames in-between. The lines appear as thin lines made by a comb on each side of the object (also known as Interlacing Artifacts). To avoid these artifacts, interlaced images are often blurred slightly to cover them up (Anti-aliasing).

A Crude Example of interlacing, is to spread your fingers, hold your hand in-front of your eyes and move your hand quickly up and down.

Progressive Scan

When Computers became every home owners dream, it was evident that TV’s wasn’t a great solution. Mainly because they used Interlaced Scan. This became especially evident when trying to read small letters on the screen. Still images would flicker and the overall image quality was poor. Progressive scan on the other hand produces crisp images with text and still images. The technique isn’t new and is as old as Interlaced Scan, but the need for low bandwidth and low-cost equipment prevailed until the technology became affordable.

The main reason that Progressive Scan is a better choice , is that it draws the image-lines sequential (1,2,3,4) instead of an alternate order (1,3,5,7 … 2,4,6,8). Resulting in sharper and better images. The drawback is that it requires larger bandwidth (because each image has to be transmitted on its own and not in pairs). By progressively scanning the image every 60th of a second (1/50 on PAL)  rather than “interlacing” alternate lines every 30th of a second, a smoother, more detailed, image can be produced. Making it perfectly suited for viewing fine details, such as text, and is also less susceptible to interlace flicker.

Progressive Scan is less bothered with artifacts and interference and the need to blur images (anti-aliasing)  to avoid those are unnecessary.

If you like a more in-depth explanation on Interlacing and Progressive signals, you can go here!

Which is better ?

To put the 720 or 1080 lines into perspective, televisions of the past had 480 lines (DVD has 576 lines).  Since more lines means a better picture then; that alone show you why the HDTV has a nicer picture than an analog TV.

(But) Oh say can you see?

Can you really see the difference in resolution between 1080i and 1080p? Tests to determine the resolution required of a television transmission system by BBC’s J.O. Drewery and R. Salmon determined that; at 9 feet, a 50 inch screen using 720p’s resolution will give you all the resolution you can see! At 9 feet, a 56″ needs 1080i to avoid showing the pixel structure.

The preferred standard most broadcasters today use is 720p (some use 1080i). Even though a 1080 sounds so much better, you should know that 1080i (interlaced) in reality produces about the same image quality as the 720p (progressive). And if you have a smaller screen (below 32″) you will not benefit from anything higher than 720p (even if the screen is supposed to handle 1080p).

Resolution

The main advantage of the new HD-standard is the 16:9 format, which suits our eyes better. Our eyes prefer wide-screen-view because it resembles the way we are designed. When it comes to monitor resolution, you get the following setup:

• 720 = 1280 x 720
• 1080 = 1920 x 1080

On a Computer monitor that is really good news. On your TV set – not so much.

What do you use it for ?

In the end, deciding between 720p, 1080i or 1080p boils down to this: What do you use it for ? Do you watch a lot of motion-intensive content then 1080p will be your best choice. Problem is that there are next to no 1080p broadcasts available (at present). Progressive scan produces more information (and requires more bandwidth) than interlaced scans and will therefor be the best choice even at 720p.

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Sources:

• http://tv.about.com/od/hdtv/a/whatisHDTV.htm
• http://ezinearticles.com/?Eye-Candy?-Which-Wins?-1080i-Vs-720p–And-What-About-1080p?&id=123148
• http://neuron2.net/LVG/interlacing.html
• http://en.wikipedia.org/wiki/Interlace
• http://www.videojug.com/expertanswer/how-camcorders-work/what-is-the-difference-between-interlaced-and-progressive-video

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