Digital printing is based on digital information as the object of communication and digital technology as the core. From the digital information, a graphic image with printable features that can be printed one by one is generated from the digital information, and imaged on the substrate with the help of an imaging device. New printing technology required. In other words, digital printing is "on-demand printing" featuring personalized printing, variable information printing, and instant printing. It can provide users with time requirements, location requirements, quantity requirements, cost requirements, and certain specific requirements. A printing service method for related services. Art copying refers to the use of copying to use precious paintings and calligraphy and cultural relics as manuscripts to form "first-class authentic works". On the one hand, it protects cultural relics, making the works of art collected in museums as "stand-ins" for everyone to watch, on the other hand, it plays the role of cultural dissemination, spreading China's cultural treasures to the world. The "one piece of printing" and "personalized printing" of digital printing just meet the characteristics of small batches of artwork reproduction and high print quality requirements. It can be said that the combination of digital printing and copying of artworks allows more rare paintings and calligraphy to be presented to the public in a more convenient and realistic manner. Here, the author takes HP Indigo 5500 as an example to introduce some methods of copying artworks using digital printing technology.

The printing material of Indigo 5500 is 80-300 grams of coated paper, 60-300 grams of uncoated paper, and the thickness is 70-400 microns. Therefore, the printing materials suitable for Indigo 5500 to reproduce works of art are special paper and rice paper. Special papers include Earl, high-end pictures, scenery, writing paper, etc .; Xuan paper is mainly machine propaganda, which adopts the mounting method, because the mounting can increase the strength of the paper and facilitate the smooth transfer of digital printing machines.

The key to copying works of art is the restoration of colors. Therefore, color management must be introduced in the digital printing system so as to obtain “reproduction of the first class”.

First, we have to prepare for Indigo 5500 color management, including three steps.

1. Clean work to ensure that printed samples are free from dirty spots.

2. Determine the transfer pressure and print the transfer pressure sample. As shown in Figure 1. We should choose the pressure of the sample with images on the left and right as the printing pressure, as shown in Figure â‘¡.

Figure 1 Transfer pressure proof

3. The calibration of Indigo 5500 itself, the purpose of calibration is to adjust the digital printing machine to the best state. Calibration is done by the system's own software and the spectrophotometer that comes with the machine. There are two types of calibration: one is called Full Color Calibration, which is a high-precision and flexible calibration method. It should be done once a week. The test chart is shown in Figure 2. Long calibration corrects 15 points on each curve of CMYK, namely 2%, 4%, 6%, 9%, 12%, 14%, 16%, 18%, 23%, 27%, 33%, 40% , 50%, 65%, 80%. The other is called Short Color Calibration, which is an economical calibration method and can be done once a day. The test chart is shown in Figure 3. Short calibration corrects 4 points on each curve of CMYK, namely 6%, 14%, 40% and 100%.

Figure 2 Long calibration test chart

Figure 3 Short calibration test chart

After completing the preparation work, you can enter the color management stage of the digital printing press. The color management of Indigo 5500 can be completed by the color management function that comes with the device, but in order to make the color more stable, the company where the author works takes the method of turning off the color management function that comes with Indigo 5500 and introducing third-party software. The work flow chart of the third-party software is shown in Figure 4. The working principle of the software is the same as that of general color management. After calibration of the device, traditional printing color characteristic files and digital printing color characteristic files are generated respectively, and the PDF files in the input hot folder are converted and sent to the output hot folder. , And then to the digital printing machine for printing.

Figure 4 Workflow of third-party software

The color management process of digital printing press includes the following three steps. â‘ Adopt printing standard ICC, such as FORGRA39.ICC as the traditional printing color characteristic file; â‘¡Use corresponding printing materials, such as special paper and rice paper, print digital color of special paper and rice paper after printing IT8.7 / 4 standard color mark Characteristic file; â‘¢ After comparing with the traditional printing color characteristic file, get the color difference, recalculate and print IT8.7 / 4 again, until the color difference of the comparison result meets the requirements and meets the standard.

The use of third-party software is to increase the cyclic calibration function of the digital printing machine, to ensure that it can be calibrated every day or every time period, and to calibrate the color difference to a minimum, thereby solving the color of digital printing proofs caused by the instability of the equipment The problem of instability, and the color characteristic file does not need to be redone. The process includes the following: â‘  After the digital printing color management is confirmed, print the TC3 test chart, and the data is used to make the calibration target value after the measurement; â‘¡ When the color changes, then print the TC3 test chart, and the data is made after the measurement The current value of the calibration; â‘¢ The color difference between the target value and the current value needs to meet the standards of the average color difference Eave <3 and the maximum color difference Emax <6. If it meets, the color calibration can be ended. If it does not meet, then the target value and current Calculate the value and store the calibration file, repeat step â‘¡.

The integration of digital printing technology in the reproduction of artworks has certain advantages and disadvantages. The advantages are as follows: â‘ The selection of substrates is diverse, in addition to rice paper, some special papers suitable for copying can also be selected; â‘¡high production efficiency and low batch cost; â‘¢suitable for the processing of graphic art derivatives. The shortcomings are: â‘  The format is limited, and large-format works cannot be printed at once; â‘¡ Professional color management technology is required as a supplement to increase investment in color management software and hardware.

All in all, the integration of digital printing technology and art copying has broadened the means of copying, and also expanded the range of applications of digital printing technology, which complement each other.

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