Offset printing image color control technology

The eternal theme of printing is the transmission and reproduction of colors. How to use different color control technologies to make the currently widely used offset printing image quality better in color reproduction is a challenge faced by domestic enterprises. In this paper, based on summarizing the world's most advanced color control technology of offset printing images, a new viewpoint is proposed for the development trend and characteristics of China's printing industry, pointing out the future direction of color control technology.

It is generally believed that due to the principle of offset printing it is an unavoidable and unstable way of printing. The "oil" in the ink and the "water" in the ink tank cannot always be combined as well as one would expect. Therefore, for printer manufacturers and consumer product suppliers, they must continue to struggle to control the entire process. process. For printers and buyers of prints, this means that they can only reach a compromised state in a fairly long calibration process, that is, to achieve "commercially acceptable quality" rather than print that can be foreseen in advance. quality.

However, this situation has changed. The current application of digital technologies in the printing and publishing industries is the key to their success. Digital technology makes color quality control and consistency control no longer a very technical thing. For example, CTP reduces the uncertainties in the process of plate making. The now-exposed version can be determined to have exactly the same plate when it is re-plated after 3 months.

The current press has very good control performance. In the printing press, the auxiliary loading device will eliminate the problems caused by the unevenness of the gasket, and the temperature-controlled roller excludes other uncertainties. The common color control methods are as follows.

1 Color control method based on ICC file

Taking readers’ digests in the United States as an example, their magazines are available in 48 editions and 19 languages. They are distributed in more than 60 countries around the world and there are 20 editions in Europe. In addition to magazines, they also distribute other products including books, such as music, video, and other special products. With the expansion of their distribution and delivery methods, the company has accordingly expanded the range of their printed products, including electronic media and traditional print media.

Image printing is the task of all print sites that print Reader's Digest. It involves a lot of repetitive work and costs. Different printing sites make different versions of image quality control almost impossible to achieve, and color management is especially a problem. Differences in color quality and appearance range from inconsistent tone to severe color deviations. For this reason, they adopted a set of Colour Systems to avoid similar problems. This is a website dedicated to managing readers' digests of all European versions of documents. Including library files, product files, images and graphics. The company has now established a new workflow to ensure consistency between different media and printing plants. In different parts of Europe, operators can access this site using special URLs and passwords to ensure consistency in printing.

Colour Systems processes the RGB image input from the drum scanner. Each scan uses a scan-correcting ICC file (also called an ICC device connection file) to convert the color of the image into the CMYK color space of the SRD (selected Reader's Digest). When needed, the scanner does frequent maintenance and inspections based on established control procedures and documentation. This ensures that both the input original image and the final output image color and ink characteristics are up to the standard, thus ensuring color reproduction and matching on the press.

2 FM screening technology combined with chroma color control

These changes have aroused people's interest in FM screening and other screening technologies. For example, Agfa's Sublima has studied the size of the smallest dot that a printer can copy in a stable manner. If the dot size is 60μm, it can represent 6% of the 150lpi screens or 8% of the 250lpi screens. In the usual case, this means that the press is limited to a relatively low resolution. With Sublima, it is possible to achieve a higher profile part without trying to print less than the minimum dot of the press, but to reduce the number of dots in the area of ​​less than 6%. Such an effect is immediate and the printing press can print network cables that are more surprising than expected, with the high-profile part appearing brighter and the middle tone being more abundant.

Creo takes a step forward in advancing the use of FM screening, but it not only emphasizes the impact of very small dots on print quality, it also promotes the application of balanced distribution of oil and water due to the consistency of its dot size. . This result is better, the printer can be controlled more consistently, the amount of ink used can be reduced, and the printing process can be better controlled. This is critical for the long version of web offset printing, which is why 40% of US magazines use FM screening for printing. As Polestar began to use Creta's Stacatto FM screening in its web offset printing shop, FM screening began to be used in British magazine printing.

Between 1970 and 1980, register control on web printing presses was a very high technology, and now there is an increase in the ability to adjust the color closed loop, that is, the ability to adapt. Once the color closed-loop control system from QTI and GMI is set up, it can ensure that the same color is maintained throughout the printing process. As the ultimate owner of QTI, QuadGraphics is trying to ensure that no artificial intervention is required on the press. In contrast, GMI is taking a big step forward in using colorimetric values ​​to achieve quantitative printing.