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Technology Events
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One of the most difficult problems in the transition to HDTV is the different aspect ratio between CDTV (and SDTV) and HDTV. CDTV has an aspect ratio of 4:3 while HDTV has an aspect ratio of 16:9. This basic imcompatibility is a mistake in many people's minds since you either need to distort, crop or envelope the image. Here is a drawing from the book that shows three ways of resolving this problem.
Looking at the left half of the image, you can see how a widescreen 16:9 or 1.78:1 apsect ratio to a 4:3 or 1.33:1 aspect ratio. The 16:9 imge is 25% larger than the 4:3 image. To see the whole picture and not distort the image, the letterboxes on the top and bottom are added. Many people don't like the lost image, so pan-and-scan can be used to view the center of the image. Finally, the image can be distorted by the decoder so that the jeep looks thin and narrow. It's an easy way to lose 20 pounds if you're on the screen. The right side of the image is the more common scenario. You've bought a new HDTV set, but you're stuck watching old analog TV. Besides blowing the image up, you have incompatible formats. Letterboxing now loses 33% of your screen that you just paid several thousand dollars for. So you switch to pan and scan, but then you can't see the tops of the mountains or the bottom part of the screen. Finally, you decide to stretch teh image and the jeeplooks like a hummer. It's going to add about 60 pounds to a 200 lb man as well. It's a poorly distorted view of the world. A popular way to watch SDTV images on your HDTV now is to do an anamorphic distortion of the image. Anamorphic distortions leave the center of the image largely unchanged, but distort the edges. The image below shows how the edge is stretched. You can see the difference in this easy comparison, but the human eye adjusts to distorted images images quickly. If you look at the images together, you notice the difference. If you look at them separately, you accept either image. The mind is very accepting with what it sees right in front of your face. Don't always believe what you see!
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