Application and Research of Display Color Management Technology
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The application of color management technology in the printing industry is becoming more and more important. In the color management process, the most important two links are the color matching between the original and the display and the color matching between the display and the printed matter or the output of the printer. In these two aspects, the display plays an extremely important "bridge" in the whole process of color management. Whether the display result of the display is accurate will directly affect the accuracy of the print output. Therefore, color management of the display is an important basis for color management.
First, the principle and method of display color management
The color management technology of the display is mainly divided into the calibration and characterization of the display. Display calibration refers to the process of setting and adjusting the optimal or specific display state. The best state refers to a neutral colorless state that matches the display to achieve optimal brightness, contrast, and a certain color temperature. A specific state is a situation that mimics the appearance of a particular environment.
The display calibration system is divided into two types according to the mode of use and principle:
1. Pure software
① usage. Software such as Adobe Gamma and MonitorCalibrator achieves an ideal or specific working state through state observation and manual setting.
② working principle. The adjustment of the effect change is done by adjusting the LUT meter of the display card. The LUT table is a table of conversion between the pixel value of the display image and the drive value of the display driver circuit.
Figure 1 Display system for card LUT calibration (using display colorimeter)
2. Software and hardware cooperation (including colorimeter or spectrophotometer)
① usage. For example, PrifileMaker, MeasureTool, EyeOne and other systems have a target state feedback detection and adjustment structure composed of a display colorimeter. The display panel button of the system can adjust brightness, contrast and color temperature, and the display interface is detected by a colorimeter. The interactive adjustment of the display data and panel buttons reaches a certain target state.
② working principle. The display effect is adjusted by changing the LUT table in the display card. After the set target state is reached, the calibrated mapping table in the display card needs to be cured. Figure 1 is a schematic diagram of the adjustment of the soft and hard mode. The characteristic is that after a certain state is set, the calibration change is obtained by the mapping method of the display card lookup table. A disadvantage of such a system is that there is no direct recovery compensation capability for the performance degradation of the display. The calibration compensation based on the display card LUT is only a mapping change under the existing display capability.
After the display is calibrated, you can do the ICC Profile in the corresponding display mode. This process is called characterization.
Second, display color management experiment and analysis
In this experiment, Eye-One Match3.0 display calibration software was used to manage the color of the display, and the accuracy of the display calibration was analyzed through experimental data.
1. Experimental equipment
Hardware: Great Wall M176 LCD monitor, Eye-One Pro colorimeter.
Software: Eye-One Match 3.0 display calibration software, ProfileMaker Pro 5.0.5, Adobe Photoshop CS3.
2. Display color management experiment
This experiment uses Eye-One Match 3.0 calibration software for color management of the display. Eye-One Match 3.0 is software for display color management.
① control of experimental conditions
a. Under the different lighting conditions, the same color will have different color appearance. Therefore, it is required to be under the same light source during the calibration and measurement of the display, establish a neutral gray environment and standardize the light source, and close the surrounding strong light, preferably using a hood. A D65 source was used in this experiment.
b. Before correcting and measuring the display effect of the monitor, first clean the monitor screen, pay attention not to squeeze the screen when wiping; turn on the monitor for at least half an hour to make it color stable; turn off the color management function and screen saver of the monitor.
② display calibration steps
a. Target setting of the display: target color temperature is set to 6500k; target gamma value is set to 2.2; target white field brightness is set to 120 cd/m2.
b. Environmental light source inspection. Whether the ambient light is appropriate will ultimately affect the success or failure of the experiment. The ambient light is always kept stable during the experiment and no glare can occur. The software comes with an automatic ambient light detection page with the black slider in the green range when the ambient light is in the proper state.
c. Contrast adjustment. Adjust the display contrast to the maximum, place the measuring device in the appropriate position, and click the start button to start the adjustment of the contrast. In this process, the contrast of the display should be constantly adjusted until the final result is satisfactory, that is, the black slider is in the green range.
d. Brightness adjustment. First set the brightness value of the display to the lowest level. After clicking the start button, increase the brightness value according to the software prompt until the black slider is in the middle of the green range.
e. Adjust the three color values of the display R, G, B. After selecting the white point color temperature, place the screen calibrator in the corresponding position and adjust the three color values of the display R, G, B until the black slider is in the middle of the green range.
f. Measure the color patches. By measuring the 42 standard color blocks that come with the software, the curve of the graphics card is automatically adjusted to match the target settings, thereby adjusting the overall performance of the display. The software automatically locates the position of the Eye-one, and the changing color patches appear. The software will make adjustments based on the color information obtained by the Eye-one and the original color information, as shown in the second.
Figure 2 Schematic diagram of measuring color blocks
3 display characterization
After the calibration is completed, the characteristic curve of the display is obtained, and the more the characteristic curve tends to be linearized, the more accurate the corrected screen is. Save the resulting ICC profile to: \WINDOWS \system32\spool\drivers\color and apply it to the system to complete the color management of the display, as shown in Figure 3.
Figure 3 Characteristic Curve Dialog
3. Display calibration results color difference analysis
Use the Macbeth ColorChecker Chart to accurately evaluate the accuracy of the monitor's profile and analyze the effects of monitor color management. The Macbeth ColorChecker Chart has 24 color patches that cover most of the colors in the color gamut, and many of them represent memory and neutral colors, such as skin color, plants, and blue sky colors (see Figure 4). Show), you can accurately evaluate the color management effect of the display.
Figure 4 Macbeth ColorChecker Chart
Open the Macbeth ColorChecker Chart in Lab mode in Photoshop, convert it to RGB mode using the created display profile, and measure the values of each color block in the Color Check24 standard color target one by one. The color difference between the measured value and the standard value is shown in Table 1. . The measured patch chromaticity values are listed in Table 1.
Table 1 Color difference between measured value and standard value
Statistical analysis of the above experimental data yielded the following results, as shown in Table 2:
Table 2 display correction color difference statistics
The above data proves that after the Eye-one Match 3.0 calibration and characterization, the display of most colors of the display is ideal, and the color management effect of the display is good.
Third, the experimental summary
Through the experimental results, after using Eye-One Match 3.0 to manage the color of the display, the average color difference is 4.04, the maximum color difference is 7.8, and the color tolerance of the printing industry is △Eab=6, so the objective evaluation from the color difference From the perspective, the color difference of the display can be accepted by the printing industry. It proves that the accuracy of the characteristic file produced by the Eye-One Match 3.0 color management software and the correct experimental method is very high, and accurate color management can be realized.
To do a good job of monitor color management, you should pay attention to the following points:
1 Before the color management of the display, the display must be warmed up for 30 minutes in advance, and the ambient light is controlled in neutral gray.
2 Select the correct display calibration software for scientific and reasonable operation. The experiment proves that Eye-One Match 3.0 color management software can achieve accurate color management.
3 Regularly adjust the display. The display ages over time, performance degrades, and the color reproduction performance of the display changes. Therefore, it is necessary to periodically compare with the proof sheet and periodically correct the display with a screen corrector. The corrected items mainly include brightness, contrast, gamma value, and type of fluorescer.
4 Do a good job in managing the display ICC files.
5 Properly save the standard proofs. If there is any discoloration, it should be replaced in time; the image files of the standard proofs should be saved permanently so that they can be used directly when the proofs fade.