Academic journal article Phi Delta Kappan

Television: Acronyms, Specifications, and Geometry

Academic journal article Phi Delta Kappan

Television: Acronyms, Specifications, and Geometry

Article excerpt

IF A NEW high-tech television is in your future, you might want to bone up on your geometry. Let me explain. In the early days of television, the National Television Standards Commission (NTSC) set the aspect ratio (width divided by height) of the television screen at 4 by 3 or 1.33. Today, you can still buy 4-by-3 sets, or you can buy a widescreen set with an aspect ratio of 16 by 9 or 1.78. Most television stations or channels still broadcast in a 4-by-3 format, so a television set with that aspect ratio makes sense.

However, if you watch a lot of movies or programs on high-definition, cable, or satellite channels, a number of these will be widescreen productions. Now here is the downside of this geometry. If you watch a 16-by-9 program on a 4-by-3 set, the screen is "letter boxed"--meaning it has black bars on the top and bottom of the screen (Figure 1, top). If you watch a 4-by-3 program on a 16-by-9 set, the image is "pillar boxed"--meaning there are black bars on the left and right of the screen (Figure 1, bottom). In either case, a sizable portion of the television screen is unused. (I should mention here that Europe and other parts of the world do not use the NTSC standard, so some of what follows does not apply to readers outside the U.S.)


There are several "work arounds" for letter boxing and pillar boxing. Most widescreen sets (16 by 9) have aspect adjustments. The most common aspect adjustment is to stretch--or widen--a 4-by-3 program to fill the widescreen. I suppose you could get used to this, but it sure makes people look plump. Going in the opposite direction, some widescreen DVD movies are also available in "full-screen" versions, but this is becoming less and less common.

A second downside to this geometry quandary is that watching a 4-by-3 program on a large widescreen set (unstretched) is like watching it on a significantly smaller 4-by-3 set. What you thought was going to look like a large picture looks a lot smaller. Here's a brief tabular presentation of effective viewing reduction for widescreen sets of various sizes. (The figures are for diagonal measurements and are in inches.)

CNet has an online calculator that will give you these comparisons for any size widescreen set at 4520-7608_7-1016109-4.html. Hint: CNet calls pillar boxing "window boxing," and remember to use the lower of the two calculators.

The bottom line is you must examine your viewing habits before you buy a new television. Of course, if you have the space, you can have a television room and a separate home theater room for your widescreen. Ultimately, most people will buy a newer widescreen set because they want to move up to High-Definition Television (HDTV) and because they like the movie theater look of the newer format.

The old television standard set by the NTSC was labeled 480i. This format had 480 horizontal lines of resolution that were, as the "i" signifies, "interlaced." That is, the television displayed the odd-numbered lines every 60th of a second and the even-numbered lines in the next 60th of a second. You can actually see these lines if you look closely at the screen. Unfortunately, viewers rarely saw a television program with all 480 lines of resolution, since most programming was produced with only about 250 lines of resolution. And interlacing causes an imperceptible flicker that can contribute to eyestrain.

The most common HDTV standards are 720p and 1080i or 1080p. Each has as many lines of resolution as the numbers suggest. The "p" stands for "progressive scan," which means that all lines are displayed at one time--not interlaced. Suffice it to say, if you buy an HDTV you should be sure it can display at least one of the standards mentioned here. Another important consideration is the number of pixels (picture elements) an HDTV can display. Most newer HDTVs have pixel ratings of about 1280 by 720. …

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