High-Definition Television


As the name implies, a form of television that increases definition (resolution) over current standards. HDTV uses digital signals versus the current analog standard. There are several picture sizes in the standard from a digital version of today's resolution to a wide-screen version designed to make television more like movies.

The umbrella term sometimes used for this is DTV (Digital Television). However, as an umbrella DTV covers more than just HDTV. It also covers standard-definition (SDTV) and enhanced-definition (EDTV) television which are also digital TV modes of operation. Combine that with the mix of other applicable terms that can be used to describe the various signals DTV can cover and you can quickly get a headache. Here is a summary to help sort things out...

Aspect Ratio

Simply, this refers to the width and height of a display. It is usually specified as a ratio. Standard TV has an aspect ratio of 4:3 which means that for every four units of width there are a corresponding three units of height of the display. This can be millimeters, inches, or yards; so long as the measurement units are the same, a standard TV will have four of them across and three of them up and down.

Widescreen TV has an aspect ratio of 16:9. This ratio is similar in nature to what a standard 35mm film would project onto a movie screen. Often times you will note this ratio when a widescreen movie is shown on standard analog TV using a letterbox where the top and bottom of the screen are black so you can see the full width of the movie.

Interlace versus Progressive Scans

These terms describe how vertical lines are displayed on the screen.

Your standard analog TV used interlaced scanning where the electron beam was scanned across the screen, moved down two pixels, scanned across the screen, moved down two pixels, etc. down the screen and then went back and rescanned the screen filling in the blank lines. So, each screen picture was really two different scans added together. The persistence of your vision and the phosphers on the screen made you think the picture was continuous.

A progressive scan, on the other hand, fills in each line on the screen, one at a time before going back to the top to start the next scan. Progressive scanning typically produces fewer artifacts for moving subjects. With interlaced scanning the object may move a small amount between the two scans and this produces a slight blur in the picture. The progressive scanned picture would be made up of individual stills so each one will be sharper and the overall picture will look sharper as a result.

The way the scan progresses is usually indicated by either an "i" for interlaced or "p" for progressive. The "i" and "p" are typically placed after the resolution of the device (the number that indicates the number of vertical scan lines in a picture).

Putting It Together

All television in the United States is supposed to be digital by mid-February 2009 however this goal has been a somewhat sliding target and, with a set-top box, you can still watch digital TV on an analog set. The difference will be that someone next door who has HDTV will see the pores in the athlete's skin where you will get the resolution of an I Love Lucy rerun[Smile].

And, speaking of I Love Lucy reruns, if you have a cable or satellite but have not subscribed to HDTV feeds then your fancy new set is still showing you the older formats only. On a large screen, this may even make the reruns look worse instead of better (unless you move back far enough).

So, expect to pay more for HDTV both in the sets and in the feeds that get shows to them.

What's Coming?

Even higher resolutions are on the books for the near future. The two most talked about are 2K and 4K. 2K has a horizontal resolution of 2048 pixels and 4K an amazing 4096 x 2160 pixel formatting. It's important to realize that at 4K you are talking about up to 50MB per frame for the video so this will demand impressive computing equipment just to decode and play a video of this format and even better equipment to do editing of such a video. But, it's not far away. RED Digital Cinema is saying that they will have a 4K camera ready in late 2006.