Printing workflow and process control of color management

As we all know, the purpose of color management is to use a combination of software and hardware to automatically adjust and manage colors in the production system to ensure the consistency of colors throughout the entire process of input, display and output, and ultimately achieve the faithfulness of colors Reproduction (what you see is what you get). So, how to implement color management quickly and efficiently? The author believes that establishing a measurable and repeatable process control system to regulate the printing raw materials, related equipment and environment, and optimizing the data flow and information flow in the printing production process can achieve unexpected results.

1. Introduction to Color Management

Definition of color management Color management is an application technology that correctly interprets and processes color information. It is recognized as the most effective solution to achieve faithful reproduction of colors and obtain stable colors repeatedly. In the entire process of copying color graphics and text information, the color management system ensures the consistency of the color and text information conversion from one device's color space to another device's color space under the premise of minimum color distortion .

Second, the color management workflow

The process of color management can be divided into four C: Calibration (Calibration), Characterization (Characterization), Conversion (Conversion) and Check (Check).

â‘  Calibration. This is the basic condition for good color management. It refers to adjusting each device such as monitors, scanners, digital proofers, and printing machines to a standard state to ensure that it meets or is accurate to the manufacturer's specifications and maintains certain stability. Make sure that the color of its performance meets or is close to the usual standards. Calibration is the foundation and starting point of color management. Its purpose is to calibrate the device and allow it to run steadily. The stability of the device is the basic condition for color management. Therefore, calibration is extremely important in the process of color management.

â‘¡ Characterization. Refers to the input or output of standard color scales on a calibrated device, and then measures these color scales to determine the color performance characteristics of the device based on the obtained data and establish a color profile (ICCProfile). The purpose is to establish the range of color expression of equipment or materials, and to record its characteristics in a mathematical way for color conversion. Characterization is an important part of color management and a prerequisite for color management.

â‘¢ Conversion. Refers to the conversion of the color of an image or other object from the color space of one device to the color space of another device. The purpose is to obtain visually consistent colors.

â‘£ Check. That is, the inspection and evaluation of color matching between various devices.

3. Printing process control based on color management

1. Control the stability of printing materials

The stability of the materials is the prerequisite for obtaining high-quality printed materials. In the daily production process, it is of great significance to strictly control the stability of printing materials such as printing plates, developer, fountain solution, paper and ink, and to ensure that stable printing materials are implemented. The premise of color management. The quality of the original plate directly affects and determines the quality of the printing plate. To produce a high-quality printing plate, we must first have a high-quality original plate as a guarantee. The configuration of developer and fountain solution should be carried out in strict accordance with the relevant specifications and requirements, and their status should be regularly monitored. See Table 1 for the content of supervision. Paper and ink directly affect the quality of printing. Therefore, the supervision of the stability of paper and ink is particularly important. Paper and ink are regulated in accordance with the relevant standards of ISO12647-2 and ISO2846-1, respectively, see Table 2 and Table 3.

2. Control the stability of printing equipment

The stable printing machine status is a powerful guarantee for obtaining high-quality and stable printed products. The printing machine needs regular maintenance and maintenance to ensure that the machine is always in a stable working state to ensure the uniformity and repeatability of the printing, thereby ensuring the quality of the printed matter.

For color management, the stability of CTP platesetters and printing presses is critical. The CTP plate-making machine can calibrate it by outputting the printing plate, analyze and adjust the output dot area ratio, so that it can obtain a linearized output result. The printing machine can use GATF or G7 test methods to evaluate and correct the state, thus ensuring the stability of the printing machine.

3. Control the stability of the printing environment

The stable production environment has a non-negligible role in ensuring the stability of printing quality. The printing workshop needs to strictly control the temperature and humidity (see Table 4). Changes in the workshop temperature and humidity will cause paper deformation and cause overprinting inaccuracy, affecting the ink and ink balance and ink marks. Problems such as drying will ultimately affect the printing quality.

4. Control the stability of printing quality

Stable printing quality can be achieved by ensuring stable dot transfer and stable ink volume. Stable dot transfer can be achieved by ensuring stable printing conditions. Stable ink volume can be controlled by controlling the density or chromaticity, such as G7 process control method.

G7 is based on the CTP computer direct plate making and spectrophotometric measurement. The neutral gray balance on the printed sheet is measured and controlled by a spectrophotometer, with bright contrast HC (HighlightContrast), bright range HR (HighlightRange) and dark contrast SC (ShadowContrast) is a new control method for controlling the quality of printing, and uses neutral gray printing density curve NPDC (NeutralPrintDensityCurve) to match the visual effect of the image.

The G7 test is performed in two steps. The CMYKRGB is controlled according to the ISO ink color standard in Table 3 during the first printing. After reaching the requirements, 1000 sheets are printed and sealed in the same state. After the samples are dried, appropriate samples are drawn and used EyeonePro Or EyeoneISIS to measure the data of the P2P standard on the proof sheet, and then manually (using G7FanGraph chart, as shown in figure 1) or draw the neutral gray printing density curve NPDC with the aid of IDEAlinkTMCurve software, and calculate and adjust the output compensation value to obtain a new RIP curve .

The second time is to print the characterization test version of the RIP curve output obtained after the first printing. First, CMYKRGB is controlled to achieve ISO related ink color standards (see Table 3), and then the gray balance is controlled to make HC , HR and SC meet the requirements of G7 (see Table 5) After the control parameters of the sample to be printed meet the requirements and the printing quality is stable, extract the data of the sample to measure the IT8.7 / 4 digital standard. According to the measurement results of IT8.7 / 4, you can make a profile (ICCProfile) that reflects the actual situation of the printing press, making full preparation for color management.

4. Conclusion

The implementation of color management should be based on stable production conditions, that is, printing materials, machine status and environment should be kept stable. Establishing an optimized process control system to ensure stable production conditions will not only help the implementation of color management, but also ensure that color management plays the largest role and promote the continuous improvement of printing quality.

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