When you watch TV, you’re only seeing half the picture…literally.
CRT television sets (CRT means cathode ray tube, basically, any analog set) work through interlacing. It’s the technology that made TV transmission possible. The typical television screen has 520 horizontal lines of resolution. To broadcast the signal, only half of those lines are displayed at any given time. So every frame consists of half of a set of lines. You can see the lines if you look really close, or if you’ve ever caught your computer monitor or TV set in video camera footage.
Digital TVs also display interlaced signals, but they display many more lines at a time. When you look at HDTVs in the store, they usually have stickers that flaunt their display stats. 1080i is the highest you can get. 1080 is the number of total lines and ‘i’ means interlaced.
Some HDTVs and some HD signals are labeled with a p instead of an i. The p stands for progressive scan, where all the lines are displayed at once. 1080p exists, but it’s extremely hard to find, and most TVs can’t process it. Aesthetes will argue over whether 720 progressively scanned lines are better than 1080 interlaced ones, but either way, it’s HD and it’s what all broadcasts will be after February 17, 2009.
So, if you get a converter box for your analog TV, you won’t be seeing 720p, 1080i or any other HD signal. You’ll be watching 520i, the same as always, but the picture may look clearer. (If you get a picture. Listen to the story to see how digital reception works.)
You may also notice a difference in sets and the way lighting is used on your favorite shows. HD has raised production standards since the high definition cameras can pick up lots more detail. A favorite anecdote of mine about this is one of a few very popular television shows that used to use duct tape to hold together silver set pieces that had fallen apart. Once those shows began experimenting with HD broadcasts, the tape was very visible and new sets had to be ordered.