Alright, dear reader. Strap in. It’s time to tackle high definition (HD) video. You’ve seen those big beautiful high definition TVs (HDTVs) at your local electronics superstore. Now you get to find out how and why HDTV is better than Standard Definition TV (SDTV), and know the right questions to ask when the blue-shirted Orcs come around to ask if you “need any help”. Be forewarned, however. This stuff is pretty technical. But I am here to guide you. Don’t be afraid.

Let’s start with what we’re familiar with: Standard-Definition TV. Whether it’s delivered via rabbit ears or cable, an SDTV picture consists of 480 horizontal lines stacked from the top to the bottom of the screen. These lines are “interlaced”, meaning that the picture is drawn in two passes of the electron gun that energizes the individual pixels and displays a color. The picture is “refreshed” 30 times per second.

There is another method of screen refreshing called progressive scanning, which updates the entire screen in a single pass or scan. Progressive scanning results in a brighter picture with no visible TV scan lines and fewer motion artifacts (the rough edges you sometimes see on moving objects). It’s a bit like film, where the entire film cell is projected onto the screen one cell at a time.

SDTV is presented in one aspect ratio, 4 (width):3 (height). This means that the picture is wider than it is tall, but it’s pretty close to square (which would be 4:4, right?) You’ve undoubtedly rented DVDs that display movies in “widescreen” format, which is more “rectangular” with an aspect ratio of 16:9. This widescreen format is great for viewing theatrical films, because our eyes have wider horizontal field-of-view than in the vertical. By filling more of our vision, we are drawn more fully into the action.

There’s one more “spec” we have to cover: refresh rate. Refresh rate is the speed at which the entire picture is redrawn, and is expressed in Hertz (Hz), or number of times per second. So, SDTV’s refresh rate would be 30 Hz. File that away for later.

Now, on to HDTV. HDTV has, generally, twice the resolution of SDTV. In broadcast HDTV, there are two standard “sizes” of pictures: 720 and 1080. As with SDTV, these numbers describe the number of horizontal lines on the screen. All HDTV pictures are “widescreen” (16:9), so the 720 format is 1280 pixels wide and the 1080 format is a whopping 1920 pixels wide. While the actual pixel dimensions are not too relevant when viewing HD content on a TV, they can wreak havoc on a small computer screen.

HDTV pictures can be either interlaced or progressive, and can refresh at different rates: 24, 30, or 60 Hz. So, if you’re viewing the specs of an HDTV and you see that the TV is capable of “1080p30”, it means 1080 horizontal lines, progressively scanned, at a 30 Hz rate. See? You had no idea it would be this easy.

So, which networks use what? ABC broadcasts in 720p. CBS and NBC use 1080i. Fox uses “Fox Widescreen High Resolution TV” which is really not HDTV – it’s more akin to a cousin called Enhanced Definition TV (EDTV). What about DVDs? Right now, high-definition programming on DVDs is not available. Those beautiful images you see displayed on the wall of HDTVs in the electronics superstore are actually sent to the place via satellite.

However, high-def DVDs are coming soon, as soon as the manufacturers settle on a format. Blu-Ray or HD-DVD? Which one will prevail? We’ll know soon.

© 2006 Peter F. Zimowski