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Snow Begone

Noise Cancelling for Video Pictures
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I recently observed someone working at a video monitor and the picture from the camera was full of snow because of the weak signal. I was thinking of ways the picture could be improved. The input was composite video; it was not modulated onto UHF.

Acoustic noise cancelling (Active Noise Control) operates by taking any periodic noise, such as is caused by reciprocating machinery, and reproducing it in antiphase. The sum of the two sources results in cancellation of the periodic noise.

Contrasting with analogue video signals, the periodic signal is the wanted signal, and the random signal is the unwanted signal. Similar Digital-Signal-Processing adaptive filtering algorithms used for extracting the periodic noise in acoustics can be employed here. Rather than using the extracted periodic signal to produce antinoise, we simply output the extracted periodic signal directly to be displayed. Group delays, through analogue-to-digital converters, processor units and digital-to-analogue converters can be a significant problem in acoustics, but this method for video signals merely uses the processor output directly, so any group delay is irrelevant.

It would take a lot of processing capability because the periodic video frames that are being repeated at about 60Hz contain so much information. Also, consecutive frames are not perfectly identical, so there would be some loss of quality where rapidly changing pictures are displayed.
skegger, May 25 2009


       This is how noise cancellation in video works. look at the developement of a pixel over consecutive frames, and make this developement more smooth. boils down to a temporal low-pass filter (although the implementation might be much more ingenius). As with any filter: You win some, you loose some.
loonquawl, May 25 2009


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