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aspect ratio
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Side-by-side comparison of standard-definition TV (SDTV) and high-definition TV (HDTV) aspect ratios using an image of an airplane. The SDTV screen is 4 units wide by 3 units tall, while the HDTV screen is 16 units wide by 9 units tall. Both screens show dashed rectangles indicating the safe action area (90 percent) and safe title area (80 percent) within the frame.
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Judy Garland as Dorothy Gale, with her dog, Toto, from the motion picture film The Wizard of Oz (1939); directed by Mervyn LeRay. (cinema, movies)
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Side-by-side comparison of standard-definition TV (SDTV) and high-definition TV (HDTV) aspect ratios using an image of an airplane. The SDTV screen is 4 units wide by 3 units tall, while the HDTV screen is 16 units wide by 9 units tall. Both screens show dashed rectangles indicating the safe action area (90 percent) and safe title area (80 percent) within the frame.
picture tube aspect ratios for SDTV and HDTV Since some of the picture information flows off the top, sides, and bottom of a television screen, the safe action area (A) is actually 90 percent of the transmitted picture. The safe title area (B) is the 80 percent of the transmitted picture that is assumed not to be hidden behind the decorative mask around the receiver tube.

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aspect ratio, when describing the visible field of an image, such as a motion picture screen, a computer display, or a television, the aspect ratio is the ratio of image width to image height.

This article was most recently revised and updated by Michael Ray.