Analog Video Blather: We're Only...
Making Plans for Nigel
http://www.youtube.com/watch?v=0C6bVckO_CM
This video includes an interesting trick that I only just now recognized, and it is one which is rarely seen these days, because it is done strictly in the analog domain. Notice the parts where the people appear to have sinusoidally displaced hair, but the background is stable?
Video overlays, like other effects, at that time occasionally included digital _control_, but were generally performed against analog inputs, and generated an analog output. "Bluescreening", or more properly _chroma keying_, gets its name from exactly that-- selecting one of two inputs based on analog color thresholds in a trigger input.
The thing about analog video, though, is that unlike a digital raster image, the number of pixels is not _per se_ fixed; rather, it is a function of time. Analog video relies on timing signals-- both for the start and end of a frame, and the start and end of each row.
The effect you see is the result of the analog horizontal timing signals (the "front porch" and "back porch" of each row) being displaced according to a sine wave. The modified signal is used as both the overlay and keying input. The second input, an unmodified signal, is used as the backdrop.
And now you know how you, too, can generate your own 1979 rock video special effect. Don't forget to add 60,000 watts of light and enough oversaturation to make the Zenith logo blur right off the television set.
Seriously, if you ever want to do something like this, let me know. I'd love to help, or at least see the result.
http://www.youtube.com/watch?v=0C6bVckO_CM
This video includes an interesting trick that I only just now recognized, and it is one which is rarely seen these days, because it is done strictly in the analog domain. Notice the parts where the people appear to have sinusoidally displaced hair, but the background is stable?
Video overlays, like other effects, at that time occasionally included digital _control_, but were generally performed against analog inputs, and generated an analog output. "Bluescreening", or more properly _chroma keying_, gets its name from exactly that-- selecting one of two inputs based on analog color thresholds in a trigger input.
The thing about analog video, though, is that unlike a digital raster image, the number of pixels is not _per se_ fixed; rather, it is a function of time. Analog video relies on timing signals-- both for the start and end of a frame, and the start and end of each row.
The effect you see is the result of the analog horizontal timing signals (the "front porch" and "back porch" of each row) being displaced according to a sine wave. The modified signal is used as both the overlay and keying input. The second input, an unmodified signal, is used as the backdrop.
And now you know how you, too, can generate your own 1979 rock video special effect. Don't forget to add 60,000 watts of light and enough oversaturation to make the Zenith logo blur right off the television set.
Seriously, if you ever want to do something like this, let me know. I'd love to help, or at least see the result.