High fidelity screen printing technology
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In image printing, screening techniques play a decisive role in the quality of printed matter. In order to improve the quality of printed matter, research on screening technology has always been an important topic in the printing industry, including the shape, size, screening angle, combination, etc. of the dot. Today, high-fidelity screening technology has become a new trend in color printing. A new technology for the steps.
Development and defects of screening technology
1. Characteristics of AM screening
At present, amplitude modulation screening technology is still widely used in printing plate making. This technology uses the mesh adjustment network to achieve continuous adjustment of image effects. It has been used for more than 100 years and has many advantages, but there are also details. Lost, screening produces defects such as moiré, rose spots, and visual collisions. In particular, the moiré phenomenon cannot be eradicated and will increase with the number of plates, so it is difficult to achieve high-line printing and difficult to adapt. Printing of four or more colors. One of the most basic criteria for measuring the quality of screening technology is to see if it can effectively prevent the occurrence of moiré. In order to achieve the best color reproduction effect of the image, although the best dot combination angle was explored in the production junior high to avoid the collision phenomenon, it could not be eradicated.
2. FM screening features
Due to some shortcomings in the AM screening technology, especially the moiré, rose plaque and tone jump, it affects the quality of the printed matter, and it is difficult to develop into four or more printing methods.
In view of the shortcomings of AM screening, FM screening (random screening) has been studied. This screening technique uses the density of dots to represent the image hierarchy, and the distribution of the dots is random. In the FM screening, there is no frequency interference phenomenon, no cable angle problem, no formation of moiré and rose spots. The size of the ink dot does not change. The change is only the frequency of dot appearance. Compared with the traditional amplitude modulation screen, the printed color print is more detailed, and it is obviously superior to the amplitude modulation screen print under the same printing conditions. FM screening can improve the quality of film output, and high-quality images can be obtained with a low-resolution photo-aligning machine. The printing has high definition, good copying effect and good stability; it is not restricted by the angle of the cable; effectively avoiding collision Net phenomenon; not sensitive to the plate error occurring during the printing plate making process; the dark tone part is not easy to paste. The FM screening technology changes the distance between the center of the dot according to the brightness and blackness of the input pixel, and the dot size is the same. Although the defects of the AM screening technology can be avoided, it also has its own shortcomings. The main problem is that the mesh is enlarged. The influence (the perimeter of the dot edge increases and the dot gain increases), the dark tone level of the reproduced image is difficult, the highlight level (skin tone, etc.) is easy to be rough, and the requirements for the materials used (such as film, printing plate, etc.) are high. Low resistance to printing.
(1) The grain size is equal due to the equal size of the dots, especially the highlights and the tone of about 25% are more obvious.
(2) The latitude of the whole production process is smaller than the amplitude modulation and screening, so it requires more detailed process control and monitoring technology than the amplitude modulation screening.
(3) The minimum dot size is too small and many presses cannot be reproduced correctly.
(4) Due to the small size of the outlets, there are still some difficulties in proofing, copying and printing.
(5) The printing plate is difficult to image, and it is not stable enough. As long as any changes occur in the traditional plate making process, it will affect the final FM grading value and reduce the reliability of the screening.
3. Mixed screening features
In order to make full use of the advantages of AM and FM screening, and to avoid the shortcomings of the two, nowadays, the AM and FM hybrid screening technologies are introduced. Hybrid screening in the high-light area and the dark-adjusted area, like the FM screening, expresses the level changes in the picture by the density of the same fine mesh points. The positions of the dots are randomly distributed and subjected to special calculations so that the dots do not overlap each other and are not excessively spaced. In order to adapt to printing, another calculation method is added, that is, a plurality of small dots are used to form a large printing dot. In the middle adjustment area, the position of the dot is random, and the size of the dot can be changed like the AM screening. Therefore, the halftone dot has both the distribution characteristics of the frequency modulation dot and the tone expression method of the amplitude modulation dot.
Hybrid screening has the following characteristics:
(1) Due to the special treatment of the position of the dots in the highlight and shadow areas, the particles in this part are reduced by a large amount relative to the frequency modulation. In addition, the combined calculation processing of the small dots improves the reproducibility and stability of the copy.
(2) The midtone area avoids the color jump phenomenon of amplitude modulation and screening because of the randomness of the position of the network. For this meal, since the number of intermediate adjustment dots is fixed, the dot density per unit area can be calculated, so that the dot density of the intermediate tone can be defined. For the printing process, the production process and equipment of conventional precision can be used to achieve high-line printing quality, and the production efficiency is not affected.
Hybrid screening technology is accompanied by CTP technology, such as FAIRDOT and Screen Vision, which is a hybrid screening technology for CTP that is aimed at high-definition printing. As the core of CTP technology, digital proofing has also launched its own hybrid screening proofing technology, which is the analog-like real-point technology. This hybrid screening technology can not only show the color, but also make the problems in the CTP process flow unobstructed. Therefore, hybrid screening will be the best choice for future image reproduction. Combined with thermal CTP imaging technology, it can produce clearer and more reproducible dot quality.
High fidelity color for high fidelity printing
Before describing the high fidelity outlets. First understand high-fidelity printing. Since the existing paper and ink cannot fully reproduce the color gamut of the natural color original, in order to improve the saturation of certain colors on the printed matter, pure, bright red is printed on the basis of the four colors of C, M, Y and K. Colors such as green, blue-violet, etc., can produce a more natural contrast and a more fresh color of the printed image. This printing method is called high-fidelity printing. For example, when printing a picture of a strawberry, you can add a red version and a green version, so that the large red color of the strawberry fruit and the green color of the green leaf are more pure and realistic, and the whole picture appears vivid and vivid.
The distribution of dots in FM screening is irregular. The distribution of silver salt particles in photographic film and photos is also irregular. As long as the dots in the FM screening are small enough, the printed matter can be close to the original and achieve high fidelity. Since the FM screening is not limited by the shallow angle of the mesh, the color reproduction range is wide, and special printing which cannot be realized by the conventional four-color separation can be produced, and multi-color printing of four colors can be performed, thereby creating a high-fidelity printing effect. High-fidelity outlets are a new standard for FM technology temples and a pure software approach. High-fidelity color adopts FM network points, and the color separation technology of more than four colors has significant development in terms of color reproduction range, printing density, definition and level compared with four-color screening technology.
1. Development of high fidelity color technology
High-fidelity color was officially used as a noun, starting with the Seybold Symposium (Boston, USA) in the spring of 1993. It showed the audience a sample printed with FM technology, which was called the preliminary result of the “High-fidelity Color” research project. -- Printed with more than four colors for color separation printing. Up to now, there are nearly 100 companies participating in this research project around the world, including most of the international companies that have a prominent position in the prepress technology field. The goal of this project is to explore a series of theories, processes and market trends brought about by the use of advanced technologies such as FM outlets and multi-color screening. At the beginning of 1994, the color separation software introduced by the Computer Research Institute of Peking University can realize the color separation of seven colors. It is based on the FM network technology and lays the foundation for high-fidelity color plate making technology.
2. The significance of high fidelity color separation technology
High fidelity printing technology is relative to four-color printing technology. In four-color printing, four colors of C, M, Y, and K inks are used for printing. In theory, it is enough to use C, M, and Y three-color inks. But in fact, due to various reasons of the process, it is also necessary to increase black ink. Similarly, the secondary colors in which the two basic colors are superimposed are also unsatisfactory, and it is necessary to add a secondary color spot color ink. For example, the red color produced by the overlapping of the two inks of M and Y is not as bright as the special red ink. Under this theoretical premise, high-fidelity printing has been produced, that is, several spot color printings have been added on the basis of four-color printing to expand the color expression ability of printed matter. The conventional color separation technology divides the color of the original into three basic colors of cyan, magenta, and yellow, and adds black to form the chromatographic range that the print can represent. This range (called color coverage or coverage umbrella) is much smaller than natural colors. In other words, the rich colors of nature can't be expressed with only four kinds of inks. One of the purposes of making prints in six-color, seven-color, and eight-color high-fidelity colors is to expand the range of color reproduction and more realistically reflect nature. Since the prints using more than four colors for color separation printing cannot be reproduced by conventional four-color separation technology, this technology has a special status in high value-added prints.
3. High-fidelity color coloring problem
High-fidelity color expands the color space that can be expressed in printing, thereby improving the quality of printed color reproduction. One of the problems solved by high-fidelity color printing is how to correctly achieve the color of the original object during the color reproduction process, and which colors need to be added in addition to the four basic colors to more accurately reproduce the original color. In general, this question does not have the same answer, because the theme of different prints is different, and the color focus that needs to be expressed is also different. According to the deficiencies of the traditional four-color ink color gamut, a multi-color printing method is proposed. However, for general and actual process requirements, there are still basic options to meet the needs of most users, such as Kupper color and Linltype-He VCF color system, the basic colors are C, M, Y, K, orange , green, purple, which is characterized by the maximum expansion of the coverage in the chromatogram, taking into account the practical aspects of production; the latter represents a larger range of chromatograms than the former, through the secondary scan to complete the color separation. The basic colors of the Pantone 6 color are C, M, Y, K, Blue, and Green. The feature is to accommodate the Pantone chromatography and reproduce Ektachrome offset chromatography as much as possible, adapting to the many 6-color presses on the market. The basic colors used by Scitex are C, M, Y, K, Red, Green, and Blue. The feature is that each component of 7 colors is generated from a set of RGB scanning operations. The basic colors used by Crosfield Hyper Color are C, M, Y, K, C, M`, Y`, which can be divided into two printings by ordinary 4-color machine. The same color ink can be added to make the local relative density exceed 2.2. To achieve an extension of the chromatographic range. But when printing, intimate friends use transparent ink. The high-fidelity color technology is well reproduced in the traditional four-color version, which is difficult to copy metallic and pearlescent colors.
Market prospects for high fidelity printing
The use of high-fidelity printing will increase production costs and the technical requirements for the production process. For example, to use more plates and inks, the cost is higher than four-color printing. In addition, there are some factors that limit high-fidelity printing to replace traditional four-color printing, such as the widespread use of multi-color printing presses, the cost of adding film, plates, proofing, and ink. In addition, creating effective color separations and combining high-fidelity pages is also an important factor limiting the popularity of technology. The use of high fidelity technology requires the addition of color separation software. High-fidelity technology also increases the requirements for pressability, generally requiring more printing units or requiring multiple presses.
At present, high-fidelity printing is still in the research and experimental stage in China, and is not widely used in commercial printing, but this does not mean that there is no market for high-fidelity printing. With the continuous improvement of people's requirements for printing quality, high-fidelity printing technology with added value will gradually become practical and commercialized, bringing benefits to printing companies. From the current market point of view, there are many prints suitable for high-fidelity printing. For example, high-fidelity printing with high-definition and high-fidelity prints that require high quality of printing and restoration can truly restore the effect of famous paintings and prevent their shape and color. Distortion, maintain color and artistic charm, enhance the appreciation and collection value. For commercial printing of advertisements, the use of high-fidelity printing will leave a deeper impression on people and improve the publicity effect. For the prints that require high quality and can be enjoyed for a long time, as well as the printing of packaging materials for the packaging, there is a great demand for high-fidelity printing.