Color Bars and How To Use 'em
by Hal Landen
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Color bars are an artifical electronic signal generated by the camera
or by post production equipment. They are recorded at the head of a
videotape to provide a consistent reference in post production. They
are also used for matching the output of two cameras in a multi-
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camera shoot and to set up a video monitor.
Before we proceed, you should know that computer monitors are
quite different from video monitors and TV sets. You are seeing this
on a computer monitor so you will not have the same kind of
controls or images as on a video monitor. In fact, if you create
graphics on a computer monitor, it's very easy to be fooled into
thinking you have a great looking graphic for your video. But the
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only real test is when you see that image on a properly adjust video
monitor.
The graphics on this page are for example only. You'll want to use
real color bars generated from a camera and viewed on a VIDEO
monitor or TV set. Send enginering feedback on this article to me at
video@videouniversity.com
To Set up a Video Monitor or TV
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1. Allow the monitor to warm up for a few minutes
2. Dim the room lights and block any reflections on the monitor
3. Feed color bars to the monitor either from a camera or "house
bars" from your editing system
4. Set the contrast also called "picture" to its midpoint
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5. Turn the chroma also called "color" all the way down until the
color bars are shades of black and white
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Diagram of Colors and Values
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6. Notice the three narrow bars labeled 3.5, 7.5 and 11.5 on the
bottom right. These are the Pluge Bars which stands for Picture
Lineup Generating Equipment. Adjust the brightness control until
the middle (7.5 units) pluge bar is not quite visible. The lightest bar
on the right (11.5 units) should be barely visible. If it's not visible,
turn the brightness up until it becomes visible.
Since 7.5 units is as dark as video gets, you should not see any
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difference between the left bar (3.5 units) and the middle bar (7.5
units). There should be no dividing line between these two bars. The
only division you should see is between 11.5 and 7.5 (Note this same
technique is used in setting the b w viewfinder on your video
camera.)
7. The next step is to set the contrast control for a proper white
level. To do so, turn the contrast all the way up. The white (100
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unit) bar will bloom and flare. Now turn the contrast down until
this white bar just begins to respond. The image below shows what it
should look like at this point.
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Correct NTSC Color Bars without Color
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The image below is INCORRECT.
ntscbwb.gif ¨
Incorrect NTSC Color Bars without Color
The above image shows a monitor whose black level (brightness) is too
high. Of the three pluge bars, only the 11.5 pluge bar should be
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visible.
NOW for the colors...
First a shortcut to adjusting hue: With a little experience you can
avoid the next two steps by simply "eye-balling" the yellow and
magneta. The yellow should be a lemon yellow without orange or
green. And the magenta should not be red or purple. And you're
done.
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But here's another way: Many professional monitors have a blue-
only switch. If your monitor has one, switch it on. If your monitor
does not have a blue-only switch, you can use a piece of blue
lighting gel. Hold it to your eye like a viewing lens. If you see any
of the red, green or yellow colors, double the blue gel over to
increase the blue effect.
By using the blue-only switch or a piece of blue gel, you have
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removed the red and green elements of the picture. Only the blue
remains. If the tint and color (also called "hue") are correct, you
should see alternating bars of equal intensity as in the example
below. With a little practice, you'll be able to eye-ball this step
fairly precisely.
8. With the blue switch on (or your blue gel in front of your eye)
turn the chroma or color until the grey bar at the far left and the
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blue bar at the far right are of equal brightness. One trick is to
match either the gray or blue bar with its sub-bar.
9. Adjust the hue control until the cyan and magenta bars are also
of equal brightness. You can also match either of them with their
sub-bars. Now the four bars - gray, blue, cyan, and magenta
should be of equal intensity. The yellow, green and red (which are
black in the diagram below) should be completely black.
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Here's a diagram:
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Blue Only Diagram
Now here's what it looks like "in color."
ntscblue.gif ¨
Correct Blue Check (minus Red Green)
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You should now have a properly adjusted video monitor. However, if
flesh tones don't look right, you may need to make further
adjustments to the chroma and hue. That's why engineers say (half
jokingly) NTSC means "Never Twice The Same Color."
1__#$!@%!#__smpte2.gif ¨
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Correct NTSC Color Bars
Here's what these same color bars look like on a waveform monitor:
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Color bars on a waveform monitor
Once you have set up your monitor, leave it alone. Unless you have a
waveform and vectorscope, its the only instrument you have to see
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how accurate your video is. This is true of your camera viewfinder,
your field monitor and your studio monitor.
After you've set up a few monitors, you'll soon know what proper
bars look like and then you'll be able to easily "eye-ball it" with a
fair amount of precision. For more information on the video signal,
see the engineering article. But before you get too technical, why
not think about making your video business more PROFITABLE!
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Also see PAL Color Bars contributed by Sheldon Kennedy.
Update: I'm grateful for the many great emails I've received about
this article. One email resulted in the article being used, with my
permission, in a sophisticated defense system. But of all the great
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email I have received, my favorite was from the Inventor of the
Color Bar Generator. I have included that correspondence in a
separate article.
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