Calibrating Video Monitors with Color Bars
Editors and broadcast designers shouldn’t rely on an uncalibrated monitor when making crucial adjustments to the color and brightness of their programs. Instead, it’s important to use a calibrated broadcast monitor to ensure that any adjustments made to exposure and color quality are accurate.
Monitors are calibrated using SMPTE standard color bars. Brightness and contrast are adjusted by eye, using the color bars onscreen. Adjusting chroma and phase involves using the “blue only” button found on professional video monitors. This calibration should be done to all monitors in use, whether they’re in the field or in the editing room.
To calibrate your monitor
Connect a color bars or test pattern generator to the monitor you’re using, or output one of the built-in color bars generators in your editor program.
Important: Avoid using still image graphics of color bars. For more information, see Y′CBCR Rendering and Color Bars.
Turn on the monitor and wait approximately 30 minutes for the monitor to “warm up” and reach a stable operating temperature.
Select the appropriate input on the video monitor so that the color bars are visible on the screen.
Near the bottom-right corner of the color bars are three black bars of varying intensities. Each one corresponds to a different brightness value, measured in IRE. (IRE originally stood for Institute of Radio Engineers, which has since merged into the modern IEEE organization; the measurement is a video-specific unit of voltage.) These are the PLUGE (Picture Lineup Generation Equipment) bars, and they allow you to adjust the brightness and contrast of a video monitor by helping you establish what absolute black should be.
Turn the chroma level on the monitor all the way down.
This is a temporary adjustment that allows you to make more accurate luma adjustments. The Chroma control may also be labeled color or saturation.
Adjust the brightness control of your monitor to the point where you can no longer distinguish between the two PLUGE bars on the left and the adjacent black square.
At this point, the brightest of the bars (11.5 IRE) should just barely be visible, while the two PLUGE bars on the left (5 IRE and 7.5 IRE) appear to be the same level of black.
Now, turn the contrast all the way up so that this bar becomes bright, and then turn it back down.
The point where this bar is barely visible is the correct contrast setting for your monitor. (The example shown below is exaggerated to demonstrate.)
When adjusting the contrast, also watch the white square in the lower left. If the contrast is too high, the white square appears to “spill” into the surrounding squares. Adjust the contrast until the luma of the white square no longer spills into surrounding squares.
Important: Contrast should only be adjusted after brightness.
Once you have finished adjusting luma settings, turn up the Chroma control to the middle (detent) position.
Note: Some knobs stop subtly at a default position. This is known as the detent position of the knob. If you’re adjusting a PAL monitor, then you’re finished. The next few steps are color adjustments that only need to be made to NTSC monitors.
Press the “blue only” button on the front of your monitor to prepare for the adjustment of the Chroma and Phase controls.
Note: This button is usually only available on professional monitors.
Make the following adjustments based on the type of video signal you’re monitoring:
If you’re monitoring an SDI or component Y′CBCR signal, you only need to adjust the Chroma control so that the tops and bottoms of the alternating gray bars match. This is the only adjustment you need to make, because the Phase control has no effect with SDI or component signals.
If you’re monitoring a Y/C (also called S-Video) signal, it’s being run through an RGB decoder that’s built into the monitor. In this case, adjust both the Chroma and Phase controls. The chroma affects the balance of the outer two gray bars; the phase affects the balance of the inner two gray bars. Adjustments made to one of these controls affects the other, so continue to adjust both until all of the gray bars are of uniform brightness at top and bottom.
Note: The step in the second bullet also applies to the monitoring of composite signals, but you really, really shouldn’t be monitoring a composite signal if you’re doing color correction.
Once your monitor is correctly calibrated, all the gray bars will be evenly gray and all the black bars evenly black.
Y′CBCR Rendering and Color Bars
Y′CBCR rendering must be supported by the codec used in a sequence in order for Final Cut Pro to render color bars with a PLUGE (Picture Lineup Generation Equipment) area that includes a super-black (4 IRE in NTSC, 2 IRE in PAL) signal for calibration. The PLUGE part of the test signal cannot be rendered using an RGB-based codec.