Calibration of the Highest Caliber
There are many reasons to love your LCD monitor. Bold color, high resolution, and bright contrast are just a few reasons that you should treasure the “face” of your computer system. But what about when your LCD monitor behaves in strange ways? Ghosting, sparkling, and rolling horizontal and vertical lines may sound like really cool special effects until these “effects” occur while you’re trying to perform important work on your computer. If the viewable area of your LCD monitor is not properly aligned, the results may include a picture that is too far to the right or left, distorted such that it strains your eyes, or simply too small for the screen. And if the colors on your monitor are a bit “off,” consider that yet another memo from your monitor that it is screaming for calibration.
All LCD monitors from General Digital employ a multifrequency input video controller that should be calibrated for each video mode that you wish to support. If performed properly, the calibration procedure need only be performed once for each video mode. By following the calibration procedure outlined below, a table of settings is created for each video mode calibrated. The good news is that the appropriate calibration values are recalled each time the LCD monitor switches from one calibrated video mode to another; just be sure to repeat the calibration sequence for each video mode you intend to support.
Below are the initial steps most frequently used to calibrate your LCD monitor. At the risk of sounding somewhat facetious, before following the steps below please be sure that the video cable is properly seated and the screws are fully engaged. Though it may be plugged in, a loose video cable can leave some pins in a position that compromises the red, green, or blue signal. In a case such as that, no amount of button pushing will resolve the issue.
1) Select the Proper Video Mode
It is imperative that you first configure your video controller, operating system, and/or application program to run at the desired resolution (e.g., 640 x 480, 800 x 600, 1024 x 768, 1280 x 1024, etc.).
Example: Host computer running Windows XP® Operating System with a 19″ SXGA resolution LCD monitor. Note that other operating systems will require slightly different steps to achieve the same setup.
a) Select the Windows® Start button.
b) Select Control Panel.
c) Double-click Display.
d) Select the Settings tab.
e) Use the sliding bar to select the maximum resolution of the LCD (in our example, that would be 1280 x 1024 pixels).
f) Click the Advanced button.
g) Click the Monitor tab.
h) Select the appropriate refresh rate. General Digital™ recommends a 60 Hz refresh rate for optimal performance. Higher frequencies may produce ghosting or introduce other anomalies.
i) Click OK twice to commit the settings.
2) Test Screen
General Digital™ recommends that you display a test pattern on the screen that will emphasize irregularities and facilitate proper calibration adjustments. A pattern of alternating on and off pixels (white and black) produces the desired effect (see Figure 1).
Pre-Windows® XP operating systems offer a means to create a test pattern for the background through the Display Properties. If you do not have the means to create a test pattern, you can select the 50% Gray Pattern supplied with the General Digital™ Display Acceptance Test Tool (DATT), which can be downloaded from the Utilities section of our web site.
3) Adjusting Horizontal Size (aka Width or Frequency)
The most critical adjustment that must be made is the Horizontal Size (often referred to as Width or Frequency). This setting is responsible for adjusting the number of pixels on a horizontal line. When the Horizontal Size setting is improperly adjusted, the 50% gray test pattern that you displayed in Step 2 will demonstrate an interference pattern typically referred to as a moiré pattern (see Figure 2). The moiré pattern will consist of a series of vertical bars across the screen. The thickness of the bars is inversely proportional to the number of bars. Step 1 in Figure 2 illustrates an LCD monitor whose horizontal size setting is off by 4 pixels, resulting in a moiré pattern consisting of 8 vertical bars. The Size setting should be decreased repeatedly until all of the vertical bars are eliminated.
4) Fine Tune (aka Phase Adjust)
This adjustment controls where the A/D adapter samples the video input waveform. Improper adjustment will result in artifacts on the screen that appear to be moving. Users may refer to this effect as “sparkling”, “marching ants” or “waterfall” effects. Adjust the Fine Tune (Phase) setting in both directions until the optimum image is achieved.
5) Horizontal and Vertical Positioning
Use the LCD monitor’s on-screen display to adjust the Horizontal Position and Vertical Position settings so that the image is centered properly on the monitor.
6) Color Temperature and Gamma Adjustment (when available)
Inherently, LCDs do not support a color gamut as large as a traditional CRT. Unless operators use sophisticated instrumentation to measure the color output of the display, calibration of the color gamut is subjectively performed. General Digital™ offers a simple calibration technique that has proven to yield desirable results.
Note: A gamma chart can be downloaded from the Utilities section of our web site, or by clicking on the graphic below.
Figure 3 is a representation of a standard gamma chart used for color correction. The gamma chart consists of four rectangular bars–one for each of the primary colors (red, green and blue) and one for gray. Running across the center of each bar are five squares displayed at 50% luminance of the surrounding area. The surrounding area contains a checker-board pattern of alternating 100% luminescent pixels and black pixels.
Note: The monitor should be running for at least 30 minutes prior to adjusting.
In a darkened room, use the LCD monitor’s on-screen display to adjust the individual color settings for the red, green and blue outputs until the center squares appear to blend into the surrounding area. Finally, adjust the brightness and contrast until the center squares nearly disappear.
Note: Repeat steps 1–5 for each video mode you wish to use.
7) Auto Color Gain
The Auto Color Gain (ACG) function is supported in the ARGB mode only and is designed to calibrate the controller to the incoming video signal. In order to calibrate correctly, the monitor must be displaying an image containing both black and white data (see illustration) when the function is used. The internal processor of the video controller chip will then execute a process to adjust the relative values of the RGB signals to achieve the best performance. The parameters of the corrected RGB values are then stored in the controller and are unaffected by the Reset Factory Defaults function.
The reference pattern in Figure 4 can be downloaded by clicking on the graphic.
This reference pattern is for 1280 x 1024 resolution and it needs to set your ARGB input source to 1280 x 1024 resolution before performing the ACG function. The position of the black vertical bar in the pattern at the right side is important. It will affect the calibration result if you are setting the ARGB input to another resolution.
Warning! If the ACG is executed without an appropriate image being displayed, then the process will set incorrect values and the display colors will be distorted. If this occurs, then it can either be corrected by performing the process correctly or, if this is not possible, then the Reset Color Gain function can be used. This function will reset the stored RGB values to a set of approximate values.
Here at General Digital, flat panel LCD monitors are our specialty. As the innovators of flat panel technology, we pride ourselves on producing high performance by adhering to high standards. This rigid attention to detail is what has allowed us to become a trusted partner with companies worldwide. Should you need further assistance, please contact us to receive the access credentials to our on-line calibration manuals.
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