Research on the Standardization of LCD Color Management
At present, the pre-press system uses the display as a pre-proofing device and relies on the color displayed on the screen to adjust the image color. Therefore, one of the keys of color management technology is to adjust the display effect of the display to the output proofing or printing effect to a close degree. The purpose of monitor color management standardization is to make the displayed image and the final output image color as close as possible.
Aiming at the color difference between different displays of the same color, through efficient, predictable and mature display color management, professional design capabilities can be enhanced to better realize what you see is what you get. This article uses the latest i1Profiler color management software and Eye–OnePro spectrophotometer to calibrate and characterize the LCD screen and evaluate the accuracy of the display's characteristic file.
1. Preparation before display calibration
Before establishing the characteristic file, the display must be in a normal state, that is, the warm-up of the display and the adjustment of the surrounding environment, so that the display device reaches a stable working state.
First check or evaluate whether the monitor is suitable for calibration, and whether it can bring professional or ideal results after calibration. If the monitor is too old, aging, unstable or does not support full color, then calibration is meaningless.
In addition, whether the environment is suitable for calibration work, the environment should not be too bright or too dark, the light source in the room is best to use D50 or D65 standard light source. At the same time, the monitor should not be close to the window, the wallpaper or the wall is preferably gray, and the desktop background color of the computer is also gray, because too flowery or bright colors will affect the vision, if possible, consider adding a hood to the monitor. Turn on the monitor for 30 minutes, turn off the strong surrounding light, turn off the system power management, and turn off the screen saver.
Right-click the computer desktop, then click "Properties", then click "Settings", select the highest color quality (32-bit): If it is an LCD monitor, adjust the "Screen Resolution" to the maximum, because most LCDs The maximum resolution of the monitor is the best point-to-point resolution; if it is a CRT monitor, adjust the "screen resolution" to the best resolution (resolution) recommended by the monitor manufacturer.
Finally, enter the main menu of monitor adjustment through the keys on the monitor. Press the "Auto Adjust" button and the monitor will automatically adjust to the factory default settings. In addition, the distance between the eyes and the monitor should be maintained at 0.50 ~ 0.67m.
Second, the color management of the monitor
After the preparation is completed, the display can be calibrated and characterized (that is, the color management of the display). There are basically four methods for display calibration and characterization: visual calibration; using the software package bundled with the display; using the software package bundled with the measuring instrument; using a separate software package that supports various types of instruments .
The eye is not a reliable instrument and is not suitable for the calibration of the device. The goal of calibration is to obtain a known, predictable color device, and the eyes are only sensitive to comparative colors, and the sensitivity to observation of absolute colors is very low. Therefore, it is recommended not to use visual calibration for color management.
The display bundled with the calibrator is not very widely used in real life, so it will not be described too much.
In real life, the color management of the display is more of two methods: using the software package bundled with the measuring instrument and using a separate software package that supports various types of instruments.
The following describes the implementation process of the color management method of the monitor by using a separate software package that supports various types of instruments for color management.
The experimental equipment is Founder's FG780_NG model LCD display and Eye–OnePro spectrophotometer, the experimental software is i1Profiler1.1 (i1Profiler is the software officially launched by X-Rite in April 2011), and the operating platform is WindowsXP system.
After the Eye–OnePro spectrophotometer is connected to the computer, start the i1Profiler software to bring up the main interface of the software. Click the "Advanced" option of "User Mode" on the right, and then click the "Monitor Color Management" option under "Monitor" in the upper left corner.
The display color management workflow is mainly divided into five steps, followed by display settings, ICC profile settings, color set, measurement, ICC profile.
1. Display settings
First, in the pop-up "Monitor Settings" interface, set the "Default Display Settings" in the middle:
The "white point" option is "CIE light source D65". Basically, the white point determines the white color on the computer monitor. By setting the white point of the computer monitor, you can determine the quality of the lighting that the colors on the screen will simulate. i1Profiler can flexibly simulate a large number of lighting conditions, such as standard light sources CIED50, D55, D65, D75, local and custom lighting values ​​that keep the color temperature constant.
The "Brightness" option is "120". The brightness of the monitor determines the overall brightness. Modern monitors can reach an extremely high brightness of 200–300cd / m2, while older monitors can barely achieve a brightness of 100cd / m2. Choose a brightness level that has a comfortable visual experience under standard working conditions: work in lower ambient lighting conditions, and lower the display brightness will make the visual effect better. If you are working in a relatively bright environment, or when matching the monitor to controlled lighting conditions, it is recommended to use a higher brightness.
The brightness of the display provides several options: 80, 100, 120, 250cd / m2, and any value from 80 to 250cd / m2 can be selected for customization. At the same time, the brightness of the display can also be set by measuring the brightness of the environment, so as to match the display and the environment. If the color temperature of the white point is the data of the measurement environment, the brightness can also be selected as "use the brightness of the white point measurement".
Other parameters remain unchanged, click the "ICC configuration file settings" icon at the bottom of the "Monitor Settings" interface to enter the next parameter settings.
2. ICC profile settings
"Display ICC profile setting" can control the creation method of display ICC profile more advancedly. According to past history, Apple computers default to gamma 1.8, and personal computers usually default to 2.2. Both operating platforms now use standard gamma 2.2, and it is recommended to use gamma 2.2 for still images in graphics applications. The gamma value is closer to the natural gamma value of modern LCD panels, which means that the i1Profiler can obtain the gamma 2.2 with only a slight adjustment.
Make sure that all the parameters of the "Display ICC Profile Setting" interface remain unchanged. Then click the "Color Block Set" icon at the bottom of the "ICC Configuration File Settings" interface to enter the next parameter setting.
3. Color set
The main interface of "color patch set" is a series of color patches used to reflect the color behavior of the display. The color patches in the color patch set are used to generate various colors. During the measurement process, these colors will provide i1Profiler with the information needed to establish a precise color mapping of the display. i1Profiler provides an optimized set of default color patches that can create accurate color descriptions for monitors. You can also add color patches in spot colors or digital images to improve the accuracy of specific colors on the display.
You can define the number of measured color blocks by yourself, which are 119 colors, 220 colors, and 478 colors. The more color blocks, the more accurate the calibration and the longer the calibration time. Here keep all parameters of the main interface of "color patch set" unchanged, that is, select "small" (119 color patches) for "color patch set size". Click the "Measure" icon at the bottom of the "Color Set" interface to enter the next parameter setting.
4. Measurement
"Monitor measurement" refers to how the color management system recognizes the color behavior of a computer monitor. I1Profiler uses the collected measurement values ​​to create a high-quality monitor ICC profile. Most computer monitors have controls for adjusting brightness, contrast, color balance, and a series of other parameters.
Generally select the "Automatic Display Control (ADC)" option in the middle of the "Measurement" interface, i1Profiler will automatically adjust the display, as shown in Figure 4. Automatic display control (ADC) can automatically control the contrast, brightness, color temperature and other states of the display without manual adjustment. This function is very suitable for notebook computers and Apple all-in-one computers, and also suitable for any desktop LCD monitor that supports ADC. Fully automatic operation, no need to adjust the buttons on the display, convenient and fast.
If you are using a high-end display such as EZIO or NEC with built-in multiple color mode settings and a wide color gamut display, it is recommended not to select automatic control, check "Manually adjust brightness and contrast", because the ADC will default to 100% For many LCD displays, the 100% contrast ratio is too high. According to experience, the contrast ratio after the LCD monitor is restored to the factory settings is the best contrast ratio. Generally, the factory contrast ratio is less than 100%.
Put the measuring instrument Eye–OnePro on the white standard instrument board, and then press the “Calibrate†button under the color block on the right side of the “Measure†interface to start calibration. After calibration, click the “Start Measurement†button to calibrate the display.
In the pop-up full-screen interface, first place the measuring instrument Eye–OnePro in the center of the display, and click the "Next" button in the upper left corner of the full-screen interface to start the measurement. First, the contrast of the display is automatically corrected. Generally, the contrast parameters of the display can be automatically corrected, as shown in Figure 6. Then automatically correct the brightness. If the monitor does not support automatic brightness correction, the Brightness Correction dialog box will pop up. Manually open the menu on the display to adjust the brightness value until the green indicator "√" appears in the quality indicator. Here, it is difficult for the unstable display to accurately match the brightness together. The brightness will move back and forth indefinitely. Carefully adjust it to ensure that the arrow is as close as possible.
Next, various color blocks in the standard reference data appear in sequence on the screen. The EyeonePro spectrophotometer automatically measures and records the spectral reflectance of each color block after display, and the screen continuously changes various colors. The automatic measurement takes about 3 minutes. After the measurement is completed, it immediately pops back to the main interface of the "ICC configuration file". At the same time, a contrast appears in the color block diagram on the right side of the main interface.
5.ICC configuration file
Name the configuration file first, and consider including the display manufacturer, model, related display settings, and date in the name. In the pop-up "ICC Configuration File" main interface, under "Configuration File Name" under "File Name:", enter "FG780_NG20120113.icc" here, "FG780_NG" in the file name is the monitor model detected by the software, "20120113" It is the current experiment date, so the file is convenient at a glance. In the long-term digital workflow, the number of configuration files is increasing day by day. When trying to find the specific configuration file you want to use, reasonable naming can save time and effort.
After entering the name of the ICC profile, click the "Create and Save Profile" button to start processing. After processing, the monitor's icc file is generated, and the generated icc file is automatically used as the configuration file of the monitor system (the monitor feature file is usually automatically placed in the corresponding location of the computer operating system WindowsXP, that is, C: / Windows / systen32 / spool / driver / color), you can observe some changes in the display color display.
After all is completed, the color gamut state and curve state of the display can also be observed on the right side of the main interface of the "ICC profile", and images can also be loaded to compare the changes before and after correction. For applications that use modern LCD displays for general purposes, it is recommended to calibrate every 4 weeks. For applications with higher color requirements, or for older monitors that exhibit large color differences over time, you may need to shorten the time interval.
The calibration and characterization of the display is relatively simple, but it is very important because it plays a key role in the entire color management process. Nonetheless, the process of calibration and characterization is an iterative process and it needs continuous improvement.
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