Overscan is a behaviour in certain television sets in which part of the input picture is cut off by the visible bounds of the screen. It exists because cathode-ray tube (CRT) television sets from the 1930s to the early 2000s were highly variable in how the video image was positioned within the borders of the screen. It then became common practice to have video signals with black edges around the picture, which the television was meant to discard in this way.
Overscan is a behaviour in certain television sets in which part of the input picture is cut off by the visible bounds of the screen. It exists because cathode-ray tube (CRT) television sets from the 1930s to the early 2000s were highly variable in how the video image was positioned within the borders of the screen. It then became common practice to have video signals with black edges around the picture, which the television was meant to discard in this way.
==Origins== Early analog televisions varied in the displayed image because of manufacturing tolerance problems. There were also effects from the early design limitations of power supplies, whose DC voltage was not regulated as well as in later power supplies. This could cause the image size to change with normal variations in the AC line voltage, as well as a process called blooming, where the image size increased slightly when a brighter overall picture was displayed due to the increased electron beam current causing the CRT anode voltage to drop. Because of this, TV producers could not be certain where the visible edges of the image would be. In order to compensate, they defined three areas: Title safe: An area visible by all reasonably maintained sets, where text was certain not to be cut off. Action safe: A larger area that represented where a "perfect" set (with high precision to allow less overscanning) would cut the image off. Underscan: The full image area to the electronic edge of the signal with additional black borders which weren't part of the original image. Fullscan: The full image area to the electronic edge of the signal (with the black borders of the image if they exist). Observable fullscan: An overscan image area which dismisses only the additional black borders of the image (if they exist).
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).