To calibrate its grayscale tracking, a display may provide only two-point white balance controls, only multipoint white balance controls, or it may provide both. If both types of controls are provided, it is generally best to adjust the two-point controls first, and then adjust the multipoint controls, if necessary.
Two-Point Grayscale Calibration – Two-point grayscale calibration is performed with two sets of white balance controls. There are high brightness Red Gain, Green Gain and Blue Gain controls that are actually individual Contrast controls for each primary color. There are also low brightness Red Offset, Green Offset and Blue Offset controls that are actually individual Brightness controls for each primary color. See the Two-Point Grayscale Adjust Help topic for information on performing multipoint grayscale calibration.
Multipoint Grayscale Calibration – Multipoint grayscale calibration is performed with typically either 11 or 21 sets of white balance controls. Red, green, and blue balance controls are provided for each of the 11 or 21 grayscale levels. Multipoint grayscale is adjusted either in 10% increments (11-point) or in 5% increments (21-point).
The advantage of calibrating a greater number of points is that it is better able to correct minor errors at each grayscale level. The disadvantage is that additional calibration points require more time to measure and adjust, so you will want to balance increased accuracy against required calibration time. As a general guideline, with a connected electronic signal generator or video processor that is controlled by the application, taking 11 measurements generally takes about two minutes to complete.
NOTE: To perform multipoint calibration, both RGB Balance charts need to be in Absolute mode, with their center target lines labeled as “0.” If the charts are in Relative mode, with their center target lines labeled as “100,” they need to be switched to Absolute mode, or the display’s gamma will not be calibrated properly. Right click on each RGB Balance chart, select “Properties,” then select “Absolute” in the Reference section.
Multipoint Grayscale Calibration Procedure:
- Configure your meter and test pattern source correctly to CalMAN and to the display, if you haven’t already done so.
- Under CalMAN Settings / Workflow Basic Options / Calibration Points, select the desired number of calibration points for the display being calibrated.
- On the CalMAN Grayscale Calibration page, press the Read Series button to measure the display’s grayscale tracking performance.
- Adjust the RGB controls to optimize the balance of red, green, and blue at each grayscale level.
- Select the 100% level on the bottom CalMAN Level Select bar.
- Press the Read Continuous button to start continuous measurements.
- Select the display’s 10 or 11 point white balance calibration mode and select the 100% (or 100 IRE) adjustment point.
- Adjust the display’s red, green, and blue controls to balance each color to the 0 center target line on the single level RGB Balance chart. (If the center target line on the RGB Balance chart is labeled “100,” see the Note above.)
- Repeat for each remaining adjustment level.
- When you have optimized the RGB at each grayscale level, perform a Read Series measurement, to view the display’s grayscale tracking performance on the full-scale RGB Balance chart and to evaluate the error on the Delta E chart. Mouse over the error bars on the DeltaE chart to view a visual representation of each grayscale color error. Color errors of 1 dE or less are typically not visible.
- Press the Read Series button to measure the display’s grayscale tracking performance.