"Color management" is one of the most popular words in the printing industry, especially before printing. Color management refers to the precise control and management of color transmission in the production process to achieve a perfect color reproduction effect.
1. Analysis of the current status of color management in printing companies
Now, printing companies basically think that color management is a matter of pre-press, and has little to do with the printing part. In fact, to achieve true digitalization and standardized production, printing companies must incorporate printing into the category of color management. If only the color management of the pre-press part is implemented, it has little significance for the actual production of the printing house. The quality of printing quality depends on the final result of printing. If the printing is missing, there is no way to guarantee the quality of the product, let alone the stable quality.
At present, many manufacturers, especially large and medium-sized printing factories, have basically implemented color management before printing, but the quality of the products has not been solved well, especially in terms of color repeatability. Color management is basically the same as a small factory. Whether the colors can be consistent or not depends on the skill of the operator. Let's take an example to illustrate, if customer A produced a leaflet at the beginning of the year, and half a year later, he would have to produce the same leaflet again. Although the film used is the same, the conditions for printing are the same, the printing machine is the same machine, and the ink is also the same brand of ink, but in order to make the color of the current sheet produced and the original one, they still have The strength of nine cows and two tigers basically met the requirements. At this time, everyone can't help but ask, haven't they already implemented pre-press color management? Why is there such a situation? This is because they did not manage the color of the printing part, that is, the printing machine did not do data management, resulting in the lack of debugging standards for the printing machine, and it is difficult to achieve a consistent production state. That is, the best field density, the expansion rate of the dots is no longer the same.
So far, many printing houses have considered that it is impossible or difficult to implement color management for printing. This view is obviously wrong. We can take a look at the developed countries in Europe and America, they have implemented color management throughout the production process, and all links have realized digital production. The operators of their printing machines can wear suits and ties to work, and the whole body is clean. It seems that it is not impossible to implement, but that the wrong view has prevented us from implementing it at all.
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Second, the implementation of color management in printing companies
The color management implementation process of the production process can be divided into three parts: prepress, plate making, and printing, which are independent and interrelated by using the black box principle. Note: Pre-press includes image processing and film output; plate-making refers to the processing of the PS version, including printing, development, etc .: as shown below:
Although the production process can be artificially divided into three parts, they are not isolated, and there is an inseparable connection between them. So how to implement color management? We know that the judgment of printing quality is actually the judgment of the quality of color reproduction. Whether the color is correctly restored is ultimately reflected in the printed matter, then, do we do it from the printing part? No, color management should be implemented as follows:
1. Implementation of the plate-making part
Because the plate-making part is very independent, there is no need to consider the pre-press part and the printing part. What we have to do is also very simple, that is to determine the printing time and developing time. You can use professional test strips (such as Brunel test strips) to print on the plate, and then use the test strips and plate densitometer to determine the best printing time and development time. Ensure that 3% of the dots on the PS version are aligned, 97% of the small white holes in the dots are not dead, and the resolution line pattern is 0.008mm.
2. Implementation of the prepress section
The main work is: calibration display instruments; calibration input equipment, such as scanners; calibration output systems (including software and hardware), such as CTF system, CTP system.
â‘ Calibration of the monitor
The purpose of correcting the display is to make the displayed image and the final output image color as close as possible. The calibration steps are as follows:
â— Warm up the monitor for half an hour after turning it on, so that the monitor is in a stable state;
â— Adjust the indoor light source to a level that can be maintained frequently, turn off the extra light source, and set the brightness and contrast of the display;
â— Turn off all desktop patterns and change the background color of the display to neutral gray, which helps to adjust the gray balance;
â— To set the Gamma value, first call up the Gamma control panel, select the appropriate TargetGamma at the top of the dialog box, that is, the target Gamma value, the general image is recommended to use 1.8, if you want to use a video recorder or film recording to output the image, Gamma only set Set at 2.2;
â— To correct the white field, first create a blank new file in Photoshop, then select a paper with the same whiteness as the printing, click the WhitePoint button, drag the triangle slider until the white in the display and the white in the pattern are as close as possible match;
â— Correct the Gamma value and adjust it with GammaAdjustment until the visual effects of the two color blocks in the two-color gray bar above the triangle slider are similar and there is no obvious boundary;
â— Correct the color balance and gray balance, click Balance, adjust the RGB tri-color slider, until there is no color in the gray scale below the slider, it is a gray level;
â— To correct the black point, click "BlackPoint" and drag the RGB tri-color slider until the dark part of the gray scale below the slider feels the same as the dark part of the gray scale in printing. After the above steps, the color calibration process of the display is completed. The color correction result will immediately affect the display of the monitor. At this time, close the Gamma window, and the settings of the Gamma window will take effect every time the computer is started.
â‘¡ Calibration of the scanner
For scanners, products produced by different manufacturers have their own unique color correction system, such as: MICROTEK's DCR (dynamiccolorrendition) dynamic color correction software, Agfa's FotoTune color management software, Tsinghua Ziguang's ImageCalibration color management software, etc. These color management software automatically perform color compensation and effectively solve the problem of color distortion of the scanned image, so that the color image has the best color effect. The use of scanner color management software is very simple. Taking DCR as an example, first put the standard color table AGFA-IT8 (used for scanning reflection drafts) and KODAKQ-60 (used for scanning transmission drafts) provided by MICROTEK in the scanner. Execute the MICROTEKCALIBRATION program, then select CALIBRATE, and press the button to activate the DCR color correction system, then the operation can be completed. When scanning general images in the future, simply check whether DCR is selected. Once selected, DCR will be automatically applied to all scanned color images.
3. Implementation of the printing section
To do this part of the implementation work, a large number of printing experiments must be done for different types of paper. Adjust the printing pressure, ink volume and water volume respectively, and print the twenty-one gray scale ruler and professional measurement and control strips (such as Brunel measurement and control strips). Perform density measurement on the printed sheets, calculate the expansion ratio of the high, medium and low dots of different color plates and calculate the relative contrast value (K) under different conditions, K = (Ds-Dt) / Ds , Ds refers to the density of the ground, Dt refers to the density of the dots at 60% to 80%, usually 75% dots. According to the principle of maximum contrast value, the best solid density of various types of paper, the dot expansion rate and printing pressure of high, middle and low key are finally determined.
4. The realization of gray balance
The realization of gray balance is the foundation of correct color restoration. To achieve gray balance, it is necessary to combine pre-press and printing. The printing machine has been digitized before, and now the printing machine is set up according to the data. The twenty-one gray scale of three-color overprinting is printed. Of course, it must be controlled by a professional measurement and control strip. At this time, you will find that the gray ladders printed in three colors are not gray, but will always be biased to a certain color. In this case, the gray can not be overprinted by adjusting the pressure of the printing press or the amount of ink, only the parameter settings of the image processing software, such as the specific parameters in the PrintingInkSetup module in the Photoshop system, By setting the dot expansion curve of each color and adjusting the size of the output dots, gray balance is achieved until the three colors are overprinted.
5. Implementation of digital proofing system
After completing the above work, if the manufacturer has a digital proofing system, it can be implemented. Let the printing machine print out the proofs, as the debugging standard of digital proofing, the proofs also need to include the IT8.7.3 color scale to generate the printed ICC curve for the digital proofing system to call. Once the digital proofing system has been debugged, it is not important to make changes in normal work, which is very important. Sometimes the customer will say that the color is wrong after reading the digital sample. The operator may directly adjust the system to meet the customer's requirements. Doing so will cause the digital proof to no longer be used as a standard sample.
3. Conclusion
After the color management has been implemented in the printing system, first of all, all the data should be sorted and archived in case of unexpected needs. Second, strengthen the awareness of digital production to ensure that the production process is truly digital management. Third, according to the actual needs to do linearization work for the equipment regularly. Only by doing a good job of follow-up work can we truly reflect the value of color management and fundamentally guarantee the quality of products.
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