Simple tweaking of the video signal can make a big difference in the quality of your video image.

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 Reference Point: Color Bars

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.

Of Waveforms and Vectorscopes

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.

Putting Them to Work

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.


Using TBCs and Color Correctors

If your decks or camcorders turned in a less-than-staggering performance after this little test, don’t
despair. A time base corrector (TBC), processing amplifier (proc amp) or other color correction device can
help you fix the problem.

A TBC restores a signal’s sync pulses, and enables you to raise the brightness of a dark scene or lower
the brightness of a “washed out” one. A proc amp or color corrector can also adjust the hue or tint and the
amount of color in the scene. It is possible to get TBCs with proc amp features. These allow you to correct
a whole range of signal problems.

If you have a TBC or proc amp, connect it between your VCR and the waveform/vectorscope. Play back
the color bar tape you just recorded.

On the TBC, the video level or brightness control adjusts overall luminance, read on the waveform
monitor. Setup, or black level, controls the position of the lowest two horizontal lines in the color bar
signal.

The hue knob controls the rotation of the color dots on the vectorscope. Chroma, or color level, controls
the distance between the dots and the center of the display.

You’ll probably find that you can get very close to the standard markings on the scopes simply by
tweaking the dials. The closer the pattern gets to the scale markings, the better your edited tapes will
look.

If you can’t afford a true TBC, a color corrector or image enhancer might do the trick. It may not have
the same adjustment range or precision as a TBC, but you can probably restore enough of the signal to
noticeably boost the quality of your master tapes.

Using a Monitor

Although TBCs/proc amps, vectorscopes and waveform monitors can take you a giant step toward
prettier, more consistent pictures, they can also take you closer to bankruptcy. Even the least expensive
professional models of these three devices, combined with a good electronic video signal generator, can tip
the scales at over $4,000.

If you don’t have that kind of cash, you can probably use some simpler tools to reliably calibrate your
gear. As noted earlier, you can use some cameras to generate color bars. “Prosumer” TBCs sell for around
$1000, and you can get a waveform monitor on a computer card for a couple hundred.

Many video monitors include a “Blue Only” switch. This switch filters out the red and green color
information from the video signal on the monitor. Used properly, this switch can make your monitor a low-
priced vectorscope.

Feed a color bar signal into a monitor and click the “Blue Only” button. Notice that half of the bars
seem to “disappear” or turn black on the screen.

With the hue or tint control properly adjusted, the two middle bars are the same intensity of blue or
gray. When the chroma or color level is properly adjusted, the two outer bars are the same intensity. When
you have both settings correct, all the bright bars have the same intensity. The spaces between the bars are
all the same dark gray or black.

First, adjust the hue and color levels with the color bar signal going directly into the monitor. Then plug
the output of your VCR or camcorder into the monitor and watch the results. The change in intensity of the
bars will tell you how well your deck plays and records video.

Use Bars Whenever You Shoot

To keep your system properly calibrated, record 30 or more seconds of color bars on every tape you
shoot.

Before you sit down to edit, calibrate that tape to your editing system using the waveform monitor and
vectorscope, or the blue switch on the video monitor. Use the TBC or color corrector to compensate for
any problems.

Doing so will make sure all of your tapes consistently look their best.

LEAVE A REPLY

Please enter your comment!
Please enter your name here