Flicker fixer

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A flicker fixer or scan doubler is a piece of computer hardware that de-interlaces an output video signal. The flicker fixer accomplishes this by adjusting the timing of the natively interlaced video signal to suit the needs of a progressive display Ex: CRT computer monitor. Flicker fixers in essence create a progressive frame of video from two interlaced fields of video.

Flicker fixers sample the NTSC/PAL output from the output device and store each scan line from the field currently being displayed in RAM while simultaneously outputting the line alternately with the corresponding neighboring lines from the field stored previously (weaving). Some more advanced flicker fixers integrated in add-on graphics cards use more sophisticated methods. Outputting the image at double scan rate essentially composes a progressive display with all lines from both fields at full vertical refresh rate. This promotes the horizontal frequency of the signal from 15.734 kHz to 31.47 kHz (in the NTSC case, numbers for PAL are slightly lower), which can be the used to drive a VGA monitor from an output device.