Primary and Secondary Color Measurement
with the ColorPro CP5000
Using a ColorPro CP5000
Overview
The CP5000 software is designed to calibrate the grayscale of a television display. This is done by first specifying a white point (D65) through the chromaticity x and y coordinates. The software will then take readings from the ColorPro sensor and compare the measured color to the reference and indicate what changes should be made to achieve the proper calibration.
CP5000 can be given a "custom white point", which need not be white (or even close to it). The software will still take measurements from the sensor, calculate the deviations, and indicate how to adjust the display for accurately reproducing the custom color.
This method can be used to very effectively measure a display's color performance in reproducing the primary and secondary colors. Manufacturers are beginning to add controls for the primary and secondary colors to their displays. This procedure gives one the ability to measure and accurately adjust these controls.
Joel Silver from ISF writes, "Many manufacturers now have important adjustments in reasonably priced HDTVs for Primary and Secondary color calibration - If you see "RGBCMY" in a HDTV's menu you should be able to deliver vastly improved color fidelity to your clients!
The major problem with deploying these adjustments has been the normal issue - figuring out the nomenclature. Our congratulations to Sencore's Tom Schulte and Eric Hernes for engineering RGBCMY offsets so calibrators can use the CP5000's CIE graphic user interface for a tool for RGBCMY calibration.
Some sets permit you to get the exact CIE color point per color - others permit alignment along a line towards the right color but not the exact saturation - either tweak improves image quality and is well worth learning! This is now part of the ISF curriculum - and the CP 5000 offsets make it easy!"
Installation of Files
Sencore has a zip file for you to use to facilitate this calibration. Click on this link to download it:
http://www.sencore.com/newsletter/Oct06/CP5000CustomColors/CP5000-Custom-Colors.zip. Extract or copy the supplied .lmr files to your computer. You can use the ColorPro install directory (C:\Program Files \Sencore \ColorPro5000) or any other convenient location. Remember where these files are located, because you will need to tell the CP5000 software where they have been saved.
Signal Generation
In order to measure a primary or secondary color, we first need an accurate source. The VP4xx series video generator can provide such a source for DVI, VGA, component, composite, S-video, and NTSC signals. First, select the signal type, format, and pattern. Then we can select the color through the "gating" control. The gating control allows us to turn on and off the individual primary color components (Red, Green, and Blue). By turning on one component, we simply have that primary color. By turning on two components we have a secondary color. The colors are generated by the following table:
| Color Components | Generated Color |
|---|
| Red | Green | Blue | White |
| Red | | | Red |
| | Green | | Green |
| | | Blue | Blue |
| Red | Green | | Yellow |
| Red | | Blue | Magenta |
| | Green | Blue | Cyan |
Table 1. The ColorPro uses primary colors to generate secondary colors.
Color Measurement
Once we have an accurate color on the display, we can measure it. But we still need to tell CP5000 what color we are measuring. This is done by loading in a "Custom Reference" color into the program. To do this, start ColorPro 5000 normally, initialize the sensor, etc. Then click on the "Recall" button in the "Custom Reference" grouping. This will bring up a file selection dialog where you can choose one of the .lmr files contained in this collection.
Figure 1. Recalling Saved Custom Reference Colors
There are two sets of primary and secondary colors. The first set is for standard definition, ITU Recommendation 601 (prefixed with "NTSC-ITU Rec 601-1"). The second set is for high definition, ITU Recommendation 709 (prefixed with "ATSC-ITU Rec 709").
Figure 2. Setting a
Custom Color Reference
You can also define your own color point using the "Setup Utility" dialog, which is accessed via the "Utilities / Setup" menu. The dialog box is shown below. After selecting the "custom" radio button, one can enter the chromaticity x and y coordinates to specify an exact color. This custom color can be saved and later recalled in the same method as above.
Now that the custom reference has been set for the color being displayed, the display can be adjusted to minimize the color error. The color error is computed by the CP5000 software, and displayed in the DExy field.
Adjusting the Display
With only a two-axis color adjustment (more-less), you probably won't be able to adjust the color primary or secondary exactly to the reference color. By adjusting the DExy number to its minimum, you will have achieved the optimal setting for the display.
Figure 3. Minimize Color Error
Figure 4. Resetting
D65 White Reference
After you have adjusted (or measured) the primary and secondary colors, be sure to reset the reference color to D65 white. This can be done using the same "Setup Utility" that is used to set the reference color, simply select the "D65" radio button, and click on the "Ok" button.
Now that the primary and secondary colors are calibrated, you can enjoy the full picture quality. The CP5000 ColorPro Color Analyzer is an excellent tool for accurately measuring and calibrating television displays for precise color reproduction.
For more information on available solutions for performing accurate calibration on all display types and technologies, call 1-800-Sencore (736-2673) or visit http://www.sencore.com.