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standard-definition television
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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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standard-definition television

electronics
Also known as: SDTV
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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.

Standard-definition television (SDTV) is a type of television broadcasting that offers a lower picture resolution compared to high-definition television (HDTV). SDTV typically has a picture structure of about 200,000 picture elements and a nearly square aspect ratio of 4:3. This format was chosen as a compromise, assuming viewers would be at a distance where the finer details of higher resolutions would not be noticeable. The transition to digital broadcasting, which began in the early 1990s, eventually led to the widespread adoption of HDTV, driving traditional SDTV sets towards obsolescence.123

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3 Britannica Sources
  1. HDTV
  2. television - Resolution
  3. television - Picture shape

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