Author: Lin Liu Caiqin water
In image printing, screening technology plays a decisive role in the quality of printed matter. In order to improve the quality of printing, research on screen technology has always been an important issue in the printing industry, including the shape, size, screen angle, and combination of dots. Today, high-fidelity screen technology has become a new step in color printing. A new technology on the stairs.
Screening technology development and defects
1. Features of AM screening
At present, amplitude modulation and screening technology is still widely used in printing and platemaking. This technology uses mesh adjustment and screening to achieve continuous image adjustment effects. It has been in production for more than 100 years and has many advantages, but there are also details. Loss, screen screening produces defects such as moire, rose spots, and visual impact, especially moire can not be eradicated, and will increase with the increase of the number of printing plates, so it is difficult to achieve high screen printing, and it is difficult to adapt Printing in more than four colors. One of the most basic standards for measuring the quality of screening technology is whether it can effectively avoid the occurrence of moire. 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 school to avoid the occurrence of the network collision phenomenon to the greatest extent, it cannot be eradicated.
2. Features of FM Screening
Due to the shortcomings of amplitude modulation and screening technology, especially moire, rose spots and tone jump, etc., it affects the quality of printing, and it is difficult to develop to printing methods with more than four colors.
In view of the shortcomings of amplitude modulation screening, FM screening (random screening) was developed. This screening technique uses the density of dots to express the image hierarchy, and the dot distribution is random. In the FM screening, there is no frequency interference, no wire angle problem, and moire and rose spots will not be formed. The size of the ink dots does not change. What changes is the frequency of dot appearance. Compared with the traditional AM screen, the printed color prints are more detailed and are significantly better than the AM screen prints under the same printing conditions. FM screening can improve the quality of film output, and high-resolution images can also be obtained with low-resolution imagesetters; high-definition prints, good reproduction, and stability; not limited by the angle of the network line; effectively avoiding collisions Network phenomenon; insensitive to the set error in the printing plate making process; the dark tone part is not easy to paste and so on. The FM screening technology changes the distance between the center of the dots according to the brightness and blackness of the input pixels 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 dots increase The influence of the edge of the dot (increasing the perimeter of the dot and the amount of dot increase), it is difficult to reproduce the dark tone level of the image, the highlight level (skin color, etc.) is easy to rough, in addition, the requirements for the materials used (such as film, printing plate, etc.) Low printing resistance.
(1) Because of the equal size of the dots, it has a grainy feel, especially the highlight part and the tone of about 25% are more obvious.
(2) The tolerance of the entire production process is smaller than amplitude modulation screening, so more detailed process control and monitoring technology than amplitude modulation screening is required.
(3) The smallest dot size is too small for many printers to reproduce correctly.
(4) Since the outlets are too small, there are still certain difficulties in proofing, copying, and printing.
(5) The imaging of the printing plate is difficult and not stable enough. As long as there are any changes in the traditional plate-making process, it will affect the final FM and screen order adjustment value and reduce the reliability of the screen.
3. Features of hybrid screening
In order to make full use of the advantages of AM and FM screening, and avoid the deficiencies of both, AM and FM hybrid screening technologies are now being introduced. Hybrid screening is the same as FM screening in the highlight area and the dark tone area, and shows the gradation changes in the picture through the density of the fine dots of the same size. The positions of the dots are randomly distributed and subjected to special calculations so that the dots do not overlap each other or the distance is too large. In order to adapt to the printing, another calculation method was added, that is, a plurality of small dots are used to form a larger printing dot. In the midtone area, the position of the dots is random, and at the same time, the size of the dots can be changed like amplitude modulation screening. Therefore, the mid-tone dots have both the distribution characteristics of the FM dots and the tone expression method of the AM dots.
Hybrid screening has the following characteristics:
(1) Due to the special treatment of the position of the dots in the highlight and dark tone areas, the particles in this part are much reduced relative to the frequency modulation screening. In addition, combined calculation processing is performed on the fine dots, which improves the reproducibility and stability of the copy.
(2) Because of the randomness of the dot positions, the mid-tone area avoids the color jump phenomenon of amplitude modulation screening. In this meal, since the number of halftone dots is fixed, the density of halftone dots per unit area can be calculated, so that the halftone dot density can be defined. For the printing process, it is possible to use conventional precision production processes and equipment to achieve high line count printing quality, and at the same time, the cross-production efficiency is not affected.
Hybrid screening technology came into being with the CTP technology. For example, FAIRDOT and screen screen Bida screening are two hybrid screening technologies for high-precision printing. The digital proofing, which is the core of CTP technology, has also launched its own hybrid screening proofing technology, namely imitation amplitude modulation real dot technology. This hybrid screen technology can not only express the colors vividly, but also show the problems in the CTP process flow at a glance. Therefore, hybrid screening is bound to be the best choice for image replication in the future. Combining with thermal CTP imaging technology can produce clearer and more reproducible dot quality.
High-fidelity color suitable for high-fidelity printing
Before describing high-fidelity outlets. First understand the high-fidelity printing. Since the existing paper and ink can not fully reproduce the color gamut of the original manuscript of natural colors, in order to improve the saturation of certain colors on the printed matter, the pure, bright red is printed on the basis of the four colors of C, M, Y, and K. , Green, blue-violet and other colors can make the printed image produce more natural contrast and fresher color sense. This printing method is called high-fidelity printing. For example: when printing a picture with strawberries, you can add a red version and a green version, so that the big red of the strawberry fruit and the green of the green leaves appear more pure and realistic, and the whole picture is vivid and bright.
The distribution of dots in FM screening is irregular, and the distribution of silver salt particles in photographic film and photos is also irregular. As long as the dots in FM screening are small enough, the printed matter can be sufficiently close to the original to achieve high fidelity. Because FM screening is not limited by the shallow angle of the screen, the color reproduction range is wide, it can produce special printing that cannot be achieved by conventional four-color separation, and can perform ultra-four-color multi-color printing, thereby creating a high-fidelity printing effect. High-fidelity network outlet is a new standard for FM network technology temple, and it is a pure software method. High-fidelity color adopts FM dots, and the color separation technology exceeds four colors. Compared with the four-color screening technology, the color reproduction range, printing density, sharpness and gradation have all been greatly developed.
1. Development of high-fidelity color technology
High-fidelity color is officially used as a term. It began in the Seybold seminar (Boston, USA) in the spring of 1993. At the meeting, the Davis company opened a gallery to show the audience a sample printed with FM dot technology. The preliminary achievements of the "High-Fidelity Color" scientific research project-the use of more than four colors for color printing. Up to now, there are nearly 100 companies participating in this research project all over the world, including most of the international companies that occupy a prominent position in the prepress technology field. The goal of this project is to explore a series of related issues in theory, process and market trends brought by the use of advanced technologies such as FM outlets and multicolor screening. At the beginning of 1994, the color separation software launched by the Computer Research Institute of Peking University can achieve seven-color separation, which is based on the frequency modulation technology and at the same time laid the foundation of high-fidelity color plate-making technology.
2. Significance of high-fidelity color separation technology
High-fidelity printing technology is relative to four-color printing technology. In four-color printing, C, M, Y, K four-color inks are used for printing. In theory, it is enough to use C, M, Y three-color inks. But in fact, for various reasons in the process, black ink needs to be added. Similarly, the secondary colors superimposed by the two basic colors are also unsatisfactory, and spot color inks of secondary colors must be added. For example, the red produced by the superposition of M and Y inks is not as bright as the special red ink. Under this theoretical premise, high-fidelity printing was produced, that is, on the basis of four-color printing, several kinds of spot color printing were added to expand the color expression ability of the printed matter. Conventional color separation technology divides the color of the original into three basic colors of cyan, magenta, and yellow, plus black, which forms the chromatographic range that the printed matter can represent. Compared with natural colors, this range (called color coverage or umbrella) is much smaller. In other words, the rich colors of nature cannot be expressed by blending with only 4 inks. Six-color, seven-color and eight-color high-fidelity colors are used to produce prints. One of its purposes is to expand the range of color reproduction and reflect nature more realistically. Due to the use of more than four colors for color separation printing, the color can not be reproduced by conventional four-color separation technology, so this technology has a special position in high value-added prints.
3. Addition of high-fidelity color
High-fidelity color can expand 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 in the color reproduction process, and which colors need to be added in addition to the four basic colors to more perfectly reproduce the original color. Generally speaking, this question does not have the same answer, because different prints have different themes, and the color emphasis that needs to be expressed is also different. According to the shortcomings of the traditional four-color ink to express the color gamut, a multi-color printing method is proposed. However, for general and practical process requirements, there are basic options to meet the needs of most users. For example, the basic colors adopted by the Kupper color system and the Linltype-He VCF color system are C, M, Y, K, and orange. , Green, and purple, which is characterized by the goal of maximizing the coverage in the chromatogram, taking into account the practical aspects of production; the latter shows a larger range of chromatograms than the former, and completes the color separation by secondary scanning. The basic colors used in the Pantone 6 color system are C, M, Y, K, blue, and green. Its characteristic is to accommodate Pantone chromatography as much as possible and reproduce Ektachrome offset printing chromatography. It is suitable for many 6-color printing machines on the market. The basic colors used by Scitex are C, M, Y, K, red, green, and blue. Its characteristic is that it produces 7 color components from a set of RGB scans in two operations. The basic colors adopted by Crosfield Hyper Color are C, M, Y, K, C, M`, and Y`. Its characteristic is that it can be printed in two times by an ordinary 4-color machine. The addition of the same color ink can make the local relative density exceed 2.2 , So as to achieve the expansion of the chromatographic range. But when printing, close friends use transparent ink. The traditional four-color version is difficult to reproduce the metallic color and pearlescent color, etc., high-fidelity color technology can be reproduced well.
High-fidelity printing market prospects
In foreign countries, high-fidelity printing has been applied in commercial printing, and as a development direction of sheet-fed offset printing, its market prospects are promising. For example, Hexchrome high-fidelity printing is a multi-color double-sided printing process, which has the advantages of single-channel, multi-color printing, high profit, and high production efficiency. Japanese printing technology is known for its high-quality and fine prints. In the field of multi-color printing, printing equipment with 8 or more colors has entered the Japanese market, and the format is mostly split, some even up to 10 and 12 colors. At the same time, 8-color A2 format and 6-color A3 format printing machines have also landed on the market. In addition, five-color double-sided printing machines have also appeared in commercial printing, but from the perspective of cost savings, product development will focus on web printing machines.
The use of high-fidelity printing will increase the production cost and the technical requirements of the production process. For example, more printing plates and inks are used, which is more expensive 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 machines, the cost of adding films, plates, proofing and ink. In addition, the problem of creating effective color separations and combining high-fidelity pages is also an important factor that limits 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 printing machine performance, generally requires more printing units or requires multiple machine printing.
At present, high-fidelity printing is still in the research and test stage in China, and it 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 move towards practicality and commercialization, bringing benefits to printing enterprises. From the current market point of view, there are many prints suitable for high-fidelity printing. For example, high-fidelity printing that simulates and reproduces famous paintings that require extremely high printing quality and reduction effect can restore the effect of famous paintings truly and clearly, preventing their shape and color Distortion, maintain the color and artistic charm, enhance the appreciation effect and collection value. For commercial printing of advertisements, the use of high-fidelity printing will leave a deeper impression on people and improve publicity. For calendars that require high-quality prints that can be enjoyed for a long time, as well as the printing of packaging and decoration materials, there is a greater demand for high-fidelity printing.
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