Measuring Widescreen
Widescreen TVs screen sizes are determined by measuring the distance from one corner of the screen to the opposite corner. If you were to draw a line on the screen where the measurement is made, it would create a diagonal that bisects the area of the screen, creating triangles of two equal spaces. This is the same method used to measure the screen size of standard screen TVs.
Aspect Ratio
Widescreen TVs come in a 16:9 aspect ratio, meaning if the width of the screen is 16 inches, the height will be 9 inches. For a standard TV, the aspect ratio is 4:3, meaning a screen with a width of 16 inches will have a height of 12 inches. The advantage of a 16:9 aspect ratio is that it allows for images to appear horizontally rather than vertically, similar to the way humans see. Our eyes are arranged horizontally, and most of the things we look at lie close to the ground, so a TV with more width allows for more meaningful screen space.
Screen Area
The use of a diagonal line from corner to corner is primarily due to tradition and ease of comparison, (the numbers are relativity small), but the actual screen area is perhaps a more important measure. Original TVs had tubes that were almost round, so using a diagonal line was appropriate to measure the size, as the diagonal was essentially the diameter of the tube. For rectangular screens, the further the aspect ratio is from a perfect square (1:1) the smaller its total screen area for a given measurement of its diagonal. For instance, a 27-inch 4:3 screen will have more total screen area than a 27-inch widescreen TV, since 4:3 is closer to a square than 16:9. In fact, for two TVs with the same diagonal measurement, the widescreen will have about 12 percent less area.
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