A system developed for television to carry more channels in the broadcast band. This system reduces transmitted bandwidth to half by displaying each video frame by two interlacing (interwoven) fields. One field carries the even video lines and the other the odd lines. Interlacing causes a certain amount of visible flicker, but in live video it is hardly noticeable. Flicker is more disturbing in PAL, where the vertical line frequency is 50 Hz, and two 25 Hz fields are displayed one after the other, than in the 60 Hz NTSC system. Interlacing is sometimes used in the computer graphics field as well, where higher resolutions can be displayed on an inexpensive monitor by interlacing the image. However, with static images, such as computer-generated text and graphics converted to video, interlacing causes more annoying flicker. Many manufacturers try to eliminate or minimize the flicker effect related to interlacing by raising the allowable vertical frame frequency in PC monitors to 70 Hz and even higher. The trend nowadays is to eliminate interlacing wherever possible, even in the video domain, by line-doubling, scaling or using 100 Hz vertical scan rate TVs and monitors.
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