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Video Feedback

Video Feedback is easy and fun for anyone with a video camera and a monitor (TV screen). To make the simplest kind, take the "video out" from the camera and plug it into the "video in" on the monitor, and then point the camera at the monitor, so the monitor displays a picture of the monitor. Now you have a video feedback loop! To get the effects demonstrated in the gallery, careful adjustments of the various knobs and dials on the camera and monitor are required. I also recommended that you get a tripod. This is especially useful for doing rotations, since the camera can be held at a fixed angle. Adjust the tripod so you can rotate the camera about the viewing axis.

Try the following general setup: turn the monitor brightness all the way down, or almost all the way down. Set the contrast somewhat higher than normal. Zoom the camera in so that the image of the monitor on the monitor is about the same size as the monitor (in other words, set the aspect ratio close to 1:1). Some rotation is important otherwise you just get a blob that is hard to stabilize. Hint: turn the monitor upside down, or put it on its side -- this is much easier than trying to mount a camera upside down on a tripod!

At this point you should be able to create lots of swirling, spinning shapes. Try fiddling with the color (B&W is usually easier to start with), phase, focus, zoom, iris, etc. If the camera and/or monitor has automatic features, turn them all off; you get better control that way. Try poking your fingers into the loop, or shining a flashlight on the screen. Experiment!

Of course, if you want to save your images, you'll need a computer with a video capture board. You can also record your creations on video tape.

Video Feedback is, mathematically, a non-linear 2D map iterated at very high speed (60 Hz). (Physically, it's an optoelectronic feedback loop.) Normally, I set the aspect ratio to about 1:1, so that the map is close to area-preserving. The non-linearities come from the lenses, amplifiers, and so on in the loop. Since there are three color channels, we can also sometimes get nice color effects due to different settings in the different color channels.

For some more details, and a way to generate fractals with video feedback, see this article I wrote which appeared in The Fractal Report 37, 1995.

Video Feedback Configuration Details

This list details the hardware and software I used to make most of the images in my gallery:

  • Videonics MX-1 Digital Video Mixer
  • Sony PVM-1341 Trinitron Color Video Monitor
  • Panasonic AG-450 S-VHS Camcorder w/ 8-80mm TV Zoom Lens
  • Panasonic WV-D5000 System Camera w/ 10.5-126mm TV Zoom Lens
  • Panasonic AG-6300 Video Cassette Recorder
  • Silicon Graphics Indigo2 w/ IMPACT Compression Video Board
  • John Bradley's XV Image Viewer
  • Jef Poskanzer's PBMPLUS Tools
  • The Gimp

Some of the images have been false colored, and many have been trimmed to eliminate artifacts such as the edges of the monitor. Some of the images have been recorded on video tape, and played back for a second trip through the mixer. Still other images were produced by feeding the output of the mixer directly back into the mixer (or via the VCR/Monitor). A few images were made using a video projector, a blank wall, a camera, and a PowerMac.


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