The most important thing you can learn about video is how to set up a color monitor properly. Even with other equip- ment such as a waveform monitor and vectorscope on hand, the monitor is still a critical part of previewing and judging the picture. As we’ll see in Chapter 7 on color theory, there is no exact correlation between the mathematical representa- tion of color and the human perception of it.
Color bars are an artifi cial electronic pattern produced by a signal generator, which may be in a video camera (most professional video cameras have a bars setting) or a sepa- rate piece of equipment on the set or as a standard piece of equipment in any video post-production facility—be it tele- cine, editing, or duplication. Color bars are recorded at the head of every 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. On top on the left is a gray bar: it is 80 IRE units. FIGURE 5.5 NTSC 75% color bars.
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Monitor Setup Procedure
To set up a monitor, start with the following steps: • Allow the monitor to warm up.
• Shield the monitor from extraneous light, but calibrate it under the conditions you will be viewing during lighting and shooting.
• Display color bars on the monitor: either from the camera or a separate generator.
• Set the contrast to its midpoint.
• Turn on the blue-only function—this makes the picture black and white. If the display doesn’t have blue only, then turn the chroma (color saturation) all the way down until the color bars are shades of black and white.
The PLUGE
Notice the three narrow bars labeled 3.5, 7.5, and 11.5 in Figure 5.6a. These are the PLUGE, which stands for Picture Lineup Generating Equipment, fi rst developed at the BBC in London.
The PLUGE was developed at the BBC. It was generated at a central location in its facility and sent by wire to each studio. This way, all of the equipment could be calibrated conve- niently. This was the PLUGE alone, not combined with the color bars.
The middle black is set at 7.5 IRE black (or in the digital realm, 16,16,16). The fi rst chip, superblack, is set at about 3.5 IRE below black, and the third chip, dark gray, is set at about 3.5 IRE above black. None of these really works to adjust a monitor to properly display 0 IRE black, so the fol- lowing procedure is standard.
• 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 analog 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. This same technique is used in setting the black-and-white viewfi nder on a video camera.
• 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 fl are. 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.
(a)
(b)
(c)
FIGURE 5.6 (a) Diagram of blue-only signal. (b) Correct monitor setup, shown here in black-and-white. (c) Incorrect luminance; notice how all three of the PLUGE bars in the lower right are visible.
FIGURE 5.7 Blue-only color bars— notice that the bands are of equal intensity and in the upper portion the large and small bars are equally gray or black.
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96 Motion Picture and Video Lighting
Adjusting Color
Color on a professional monitor is referred to as “phase.” With blue only on (and thus a black-and-white picture), adjust phase until the bars are uniformly black or white. It is possible to eyeball the yellow and magenta. This is the down- and-dirty method and should be used only if other meth- ods are not practical. The yellow should be a lemon yellow, without orange or green. And the magenta should not be red or purple. This quickie method is not recommended except in emergencies. This applies to SD monitors only. In HD, it is not possible to adjust phase. However, if you are using a downconverter on the camera with an SD monitor, this adjustment will still be necessary. A standardized test chart (Figure 5.9) can be helpful for this.
Blue-Only Adjustment
Most professional monitors have a blue-only switch. This turns off the red and green guns, leaving only the blue (Figure 5.7). If your monitor does not have a blue-only switch, you can use a piece of blue gel (full CTB) or a Kodak Wratten #47—the purest blue in the wratten series. View the moni- tor through the gel. 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 hue is correct, you should see alternating bars of equal intensity.
• With the blue switch on (or your blue gel in front of your eye) turn the chroma or color until the gray bar at the far left and the blue bar at the far right are of equal brightness. You can also match either the gray or blue bars with their sub-bars.
FIGURE 5.8 A typical setup for the test chart. In this case, two Tweenies at a 45° angle are at exactly the same distance and angle from the Chroma du Monde chart for even lighting. Each Tweenie has a double scrim in it to reduce the light. This is for setting backfocus, which requires that the lens be as wide open as possible.
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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 Figure 5.6a) should be completely black.
Once you have set up your monitor, leave it alone unless the viewing conditions change—by leave it alone, I mean don’t turn the brightness up just so you can see focus bet- ter, for example. Don’t forget to go through the same process with your viewfi nder. Most professional video viewfi nders are black and white so you will only need to adjust bright- ness and contrast; however, it is critical that they be set properly to color bars.