Video Editing: Put Your Best Signal Forward

Properly calibrate your editing system, and your edited masters look almost as good as your originals. The colors look vivid and accurate, not washed out or muted. Brightness and contrast are good, and you see a generally sharp, clear image. Leave your system uncalibrated, however, and there's no telling what you'll get.

To keep your videos looking their best, here are tips on how to use a few basic tools, and a few not-so-basic ones, to tune up your editing suite. Even the inexpensive options can improve picture quality in your projects.

The NTSC video standard (the one used by nearly all video gear in North America) is built around the color bar pattern: a group of six vertical bars of color and one white bar.

Use the color bar pattern to measure how well your deck or camera captures, records and reproduces video signals. You can judge the performance of a camera or VCR based on how well it reproduces the color bar pattern.

Most video equipment shops carry printed color bar patterns perfect for shooting with your camcorder. These work well for videographers on a budget or whose tapes won't screen outside a circle of family and friends.

For a more dependable, higher-quality color bar image, get an electronic color bar generator (some cameras have color bar generators built into them). These devices plug directly into the Video In on your deck or camcorder and provide the cleanest possible signal.

Color bars are to video production what North is to navigation: a reference point.

If you know which way is North, you can deduce any other direction by looking at a compass. If you wonder at any time which way is North, a quick glance at a compass tells you.

Videographers have their own version of a compass: a waveform monitor and a vectorscope. These tools help isolate and correct video problems by using the color bar pattern as a reference.

A waveform monitor shows you the synchronization (sync), or timing information, and the luminance, or brightness, of a video signal. It displays timing information horizontally, and luminance information vertically.

Most waveform monitors display sync information many different ways; the manual should explain the differences between modes and when they're appropriate or helpful.

On the horizontal scale, watch for a rock-steady waveform that doesn't slide to the right or left as your tapes play back. Any movement may indicate a problem with the video sync pulses on the tape. (Sync pulses are the "triggers" embedded in a video signal that tell the TV set or monitor how to decode the images.)

The vertical scale on a waveform monitor is measured in IRE (Institute of Radio Engineers) units, or units of brightness. Zero IRE represents total black, 100 IRE is total white. The display has lines spaced every 10 IRE, and bold markings at zero, 100 and 7.5 IRE.

Ideally, a video signal should never dip below 7.5 IRE or rise above 100 IRE. Setup black or just plain black, at 7.5 IRE, is the "darkest" signal safely reproduced by all VCRs, cameras and TV sets. The brightest white, at 100 IRE, is the most equipment can handle without distorting. If signals on your tapes exceed either of these limits, they may not play back properly.

A vectorscope shows how your decks record and playback color information. It's even more like a navigator's compass because the display has a polar scale instead of a horizontal or vertical one.

Colors in a video signal show up at different degree marks around the vectorscope display, much as directions appear around the edge of a compass. The intensity of each color varies with its distance from the center.

A bright blue color, for example, will appear as a dot near the outer edge of the display along the blue color axis. A darker blue will appear along the same axis, but much nearer the center.

Color bars and the devices used to measure them can help you calibrate your system and improve the images in your videos.

Start by feeding a color bar signal through a waveform monitor and/or vectorscope, and then into a video monitor.

On the vectorscope, notice where the dots and lines appear on the displays. They should land within the small boxes. (If they don't, rotate the scale display knob until they're as close as possible.)

On the waveform monitor, the bars' signal forms a sort of interlaced staircase, with each bar peaking at different IRE lines on the display. The tallest of these bars should rest on the 100 IRE line. The lowest should sit on the 0 IRE line, and the line just above it should rest on the 7.5 IRE line.

Now record a few minutes of color bars on a blank tape. Do this either by feeding the electronic color bar signal into the deck's Video In, or shooting a printed color bar chart with your camera. (Understand that shooting the printed chart yields a less precise color bar pattern.)

Connect the output of the VCR or camcorder to the input of the waveform and/or vectorscope. When you play back the tape, notice the difference in results between what you saw from the color bar generator and what's on tape. The better the format, the more closely the dots and lines will match the raw output of the color bar generator.

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