Case Analysis of Three Steps in Color Management

As the digitization process goes deeper into every aspect of newspaper printing, the urgency of color management becomes stronger. The printing company of the Henan Daily Press Group has also done some experimental work, but found that it is very difficult to make this job more ideal and the impact factors are numerous. At the time, the factory did not have a whole process. Process equipment, process characteristics, control methods, and data controls are all relatively familiar to the technical personnel. Until the cooperation with Peking University Founder in the implementation of Easy Color Services and the use of digital proofing, color management established a basic framework throughout the entire process. Over the past year, color management has been continuously optimized and played an increasingly important role in the printing of newspapers.

In previous work, when the printing effect of pictures or advertisements was not good, the picture production staff (hereinafter referred to as the graphic staff) and the printing shop pushed each other, and the personnel responsible for quality management suffered from no effective evaluation means. The recurrence of the problem cannot be solved. After using Easy Color Services, we found that Easy Color Service simply means taking color management as the core, controlling the entire printing process flow, and standardizing operations through the training of relevant personnel. The practicality and pertinence of this service project are very strong, and later facts prove that the overall effect is still relatively satisfactory.

The first step in color management - calibration

This step is the commissioning and rectification of all equipment, instruments and work environment in the printing process to ensure the standardization of the entire process and data operation and stable operation. For example, the fluorescent lamps of the graph posts are replaced with the three-color lamps of the standard light source; the printing console is replaced with a standard light source; the display of the sweeping post is replaced with a more professional monitor. At the same time, the scanner correction plays an important role in the correct acquisition of photo manuscript data.

The accuracy of the screen display has an important influence on the image processing effect. In the past, we have always had the phenomenon that the screen display is good, but the printing effect is not ideal. Aside from the stability issues in the printing process, the difference between the display effect and the printing result is also an important reason. In addition, the characteristics of newspaper printing also determine that the processing of the original should conform to human visual habits as much as possible, and the accuracy of the screen display at this time is particularly important. After using BeiDing Founder's digital proofing, we have enhanced the predictability of printing results and found that the problems can be immediately corrected. However, the image processing process is a continuous loss process, and simple repairs cannot fundamentally solve the problem. If the screen display effect can approach the printing effect, many repetitive tasks can be avoided and the work efficiency can be greatly improved.

In the filming and printing section, it is mainly to ensure the quality of the transfer of the film to the plate through the network. In order to make the degree of distortion of the dots in the most ideal range and to take care of the optimal ratio of the ink content of the text and headline words, we set the film density to 3.8±0.1 (based on Agfa film). If the density is low, the quality of the plate will be reduced; on the contrary, the distortion of the intermediate tone and the increase of the film fog will be caused.

The second step of color management - characteristic test

Of course, the closeness of the color display does not obscure the difference caused by the difference in color space. The pictures used for printing must be converted from RGB mode to CMYK mode, and the color space of the picture four-color mode is determined by the actual printing environment. It is necessary to maximize the ability of the printing machine to restore color and levels while avoiding overcorrection. , and also take into account the different types of pictures in the printing process differences.

Data acquisition in the printing process plays an important role in the color management of the entire process. If there is not a basic understanding of the data in the printing process, then not only the pre-press data processing has no reasonable basis, and the print reproduction cannot be achieved. Stable and consistent. This requires an important job - a print test, which is the basis for forming a color management profile. Based on the related data control project in Photoshop software, we tested the following on our factory's printing press (mainly the German Kobao press): density, gray balance data, minimum and maximum dots, maximum ink volume, and dot gain. Network transfer quality, etc.

In the beta version, we made different content to test the corresponding data. In the gray balance part, we made 3 sets of different data. The data range was 10% to 50% of the C version. Through the control of the density uniformity, the three groups of data are observed to be closer to the actual printing environment gray balance data. Regarding the maximum amount of ink, we made several sets of comparative data. The total ink volume was from 240% to 280%, the maximum K version was 90%, and 6 levels were decremented by 10% to observe dark reproduction. The minimum and maximum quality of the outlets and outlets are mainly determined by visual inspection.

The results of the print test show that the gray balance data chain is relatively close to swop (newsprint), but the C version data must be 3% to 5% larger, and the M version data should be 2% to 3% smaller. 3% of outlets can transfer completely and steadily. The difference between 90% and 95% of outlets is not easy to distinguish with the naked eye. The relative outlets at 50% increase around 30%. The maximum amount of ink is relatively suitable at 260%. Once it is large, the dark tone level cannot be distinguished. When it is small, the maximum density will be low, which will affect the contrast of the picture. The quality of outlets is ideal. Of course, this has a good relationship with the paper used. For newsprint printing, the overall quality of the paper has the greatest impact on the quality of the print.

The third step of color management - conversion

In fact, we do the first two steps to look for data support for the conversion in order to ensure that the color space conversion is based on and more accurate. Open a picture in Photoshop, first to convert to CMYK mode, control the conversion process and affect the function of the four-color data structure is achieved in the "color settings", the most important content in the "CMYK workspace" . The selection of different "ink colors" not only determines the data distribution of the various channels during the transition from the other color mode pictures to the four-color mode, but also affects the display effect of the four-color mode pictures on the screen. The gray-axis coordinate graph also shows the balance of the data chain. We first selected the swop (newsprint) mode, and then adjusted some of the ink color in this mode. The black structure was adjusted, the largest black version. It is set to 90%. By adjusting the dot size of the monochrome version, the gray balance parameter is adjusted and the maximum ink volume is set to 260%.

Digital proofing also plays an important role in the color management of the entire printing process. For prepress jobs, problems can be discovered in advance and solved in time; for printing jobs, the stability and consistency of the quality of printed products can be guaranteed, and color can be avoided. Subjective human influence on control.

For us, color management is not only a problem of the conversion and control of a color space, it must emphasize the subjective factors of operators. We have highlighted the management of personnel in the following areas. 1 The selection of personnel requires that the graphic personnel first have talents, and the eyes that are healthy and have a keen insight and grasp of color are basic guarantees for an excellent operator to rapidly become talented and have more room to rise. The style is practical yet active and rigorous. Innovation consciousness is an important quality; 2 job training, training of the basic knowledge and operation skills of the operator of the graphic system position is a strong guarantee for the improvement of the image processing quality; 3 system construction and rely on the system to create a harmonious, innovative and motivating The atmosphere and environment are the guarantee for the continuous improvement and deepening of color management. We first conducted the preliminary transmission, assistance, and take-away by the Founder engineers during the implementation of the Yicai Service, followed by training to improve the class, invited experienced technicians from all over the country to give lectures, and received good results. Through on-the-job training, the drawing system People's ability to use the common tools of Photoshop software, color and gray balance control capabilities, the ability to grasp the color space of the picture has greatly improved.

After nearly one year of practice, the quality and print quality of the Henan Daily Newspaper Group have been significantly improved, and the concept of standardized operation and data control has also been strengthened. At the same time, we also realized that the application of color management in newspapers is not long, but there are many features. There are still many problems that need to be discussed and studied. The improvement of color management also requires a lot of pioneering work.

Source: Digital Printing 2005.8