Color bars are an artificial 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-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 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.
To Set up a Video Monitor or TV
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 5. Turn the chroma also called “color” all the way down until the color bars are shades of black and white
Diagram of Colors and Values
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 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 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.
Correct NTSC Color Bars without Color
The image below is INCORRECT.
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 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 magenta. The yellow should be a lemon yellow without orange or green. And the magenta should not be red or purple. And you’re done.
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 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 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.
Here’s a diagram:
Blue Only Diagram
Now here’s what it looks like “in color.”
Correct Blue Check (minus Red & Green)
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.”
Correct NTSC Color Bars
Here’s what these same color bars look like on a waveform monitor:
Color bars on a waveform monitor
Once you have set up your monitor, leave it alone. Unless you have a waveform and vectorscope, it’s the only instrument you have to see 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.
Reference: Hal Linden