Philip I Nelson
ComputerEyes Video Digitizer
This month we'll look at Computer-Eyes, an affordable color video digitizer from Digital Visions in Needham, Massachussets. Video digitizers aren't exactly new; various eight-bit versions have been around for years. But the ST version has been available for only a short time.
From A To D
It's the job of a video digitizer to convert analog data from the world around us (light waves or sound vibrations, for instance) into a series of ones and zeros, or digital values, which a computer can handle conveniently. A device that performs such a conversion is known, not surprisingly, as an analog-to-digital converter, and that's what is contained in the fairly large cartridge that houses the hardware part of the ComputerEyes system.
Apart from a cord to the out-board 9-volt power supply, there's nothing on the outside of the cartridge but a phono jack for video input. Into that jack you can send the signal from any standard compositive video source: a VCR, video camera, videodisc player, a TV set with video output, or even another computer.
A comprehensive program, also included in the package, allows you to capture, fine-tune, and store an image as a NEOchrome- or DEGAS- format disk file. At that point, you can treat the image like any other picture file; you can enhance it with a paint program, display it in a slide-show, make a hardcopy printout, and so on.
Hold That Pose
Video images consist of a huge amount of data. Even at top processing speed, it takes the ST a minimum of several seconds to capture and store the raw image data in memory; during that time the scanned image must be absolutely motionless. In other words, ComputerEyes is not a "frame grabber"—you can't feed it changing input like a live TV broadcast and expect it to freeze the action unaided.
One solution is to record the image on videotape and then freeze it on replay for digitization. I've had excellent success using ComputerEyes with an eight-millimeter camcorder. The camcorder has onboard VCR capabilities, including a very stable pause mode. Once you've shot the tape, digitizing is simply a matter of replaying to the desired frame, pausing, and clicking Capture on the ComputerEyes program's dialog box.
Not Just A Brownie
The first temptation when you get a digitizer is to use it like a Brownie camera, digitizing everything in sight to see how faithfully the computer can reproduce reality. The figure accompanying this column was shot on eight-millimeter videotape and then was digitized using the program's 16 gray-scale mode (which actually gives you eight shades of gray plus eight colored tints of gray, since the ST's color palette has only eight pure grays). After saving the image as a lo-res DEGAS file, I switched to the monochrome monitor and converted the lo-res picture to hi-res so it could be typeset in black and white.
You lose a bit of detail in converting from color to monochrome, since the lo-res colors are replaced by various fill patterns. But the figure gives you a reasonably accurate idea of what is possible. The major obstacle to finer resolution comes not from the digitizer, but from the ST itself, which is limited to a 16-color palette and three different screen resolutions.
Snapshots are amusing, but the system allows you to do much more. When you capture an image, ComputerEyes initially stores it in memory as a huge table of raw numbers. Depending on what options you've chosen, the program then calculates the best color value for every pixel on the screen, displaying the result as soon as the calculations are finished. But the raw data remains in memory until you take another picture or save the current one to disk. As long as the raw data remains, you can adjust the contrast, brightness, and RGB values of the picture and then recalculate it for a new display. Sometimes a small adustment makes a dramatic change in the final image, and this scheme offers you a considerable degree of creative control.
Video digitizers aren't for everyone, but the reasonably priced ComputerEyes system is simple to use, and it offers just about every feature a home user could want.