High fidelity printing screen technology

In image printing, screening technology plays a decisive role in the quality of prints. In order to improve the quality of printed matter, the research on screening technology has always been an important issue in the printing industry. This includes the shape, size, angle, and combination of dots. Nowadays, high-fidelity screening technology has become a new leap in color printing. Steps of a new technology.

First, the development and defects of screening technology

1. Characteristics of AM screening

At present, AM screening technology is still widely used in printing plates. This technology adopts a mesh adjustment network to achieve continuous adjustment of image effects. It has undergone more than 100 years of production and use, and has many advantages, but there are also details. Loss, screening creates defects such as moire, rose spots, and visual impingement. In particular, the moire phenomenon cannot be eradicated and will increase with the increase in the number of printing plates. Therefore, it is difficult to achieve high screen printing and it is difficult to adapt. Four-color printing. One of the most basic criteria for measuring the quality of screening technology is whether it can effectively prevent the occurrence of moire. In order to make the image achieve the best color reproduction effect, although the best dot combination angle was explored in the production junior middle school to avoid the collision phenomenon to the maximum extent, it still cannot be eradicated.

2. FM screening features

Because there are some defects in the AM screening technology, especially the moiré, rose spots and gradation leap, etc., the quality of the printed matter is affected, and it is difficult to develop the four-color printing mode.

For the defects of AM screening, FM screening (random screening) is studied. This screening technology uses the density of dots to represent the image hierarchy, and the distribution of dots is random. In frequency modulation screening, there is no frequency interference phenomenon, there is no problem with screen angle, and moiré and rose spots are not formed. The size of ink dots does not change the era. The only change is the frequency of outlets. Compared with traditional AM screening, printed color prints are more detailed and clearly superior to AM screen printed products under the same printing conditions. FM screening can improve the output quality of the film, and high-resolution images can be obtained with the low-resolution photo-composing machine. The prints have high definition, good copying effect, and good stability; they are not limited by the angle of the screen; they effectively avoid collisions. Phenomenon; insensitivity to overprint errors in the process of printing plates; FM screening technology is based on the input pixel brightness and blackness to change the distance between the center point and the network size is the same, although it can avoid the defects of the AM screening technology, but it also has its own shortcomings, the main problem is the increased network The influence (periphery of the perimeter of the edge of the network increases, and the increase in the number of outlets increases). It is difficult to reproduce the dark tone level of the image, and the high-light level (skin color, etc.) tends to be rough. In addition, high requirements are imposed on materials used (such as films and plates). Low resistance to print force.

(1) Due to the equal size of the dots, there is a graininess, especially in the high-light part and the tone of about 25% is more pronounced.
(2) The latitude of the entire production process is smaller than that of the amplitude modulation screening and requires more detailed process control and monitoring techniques than the amplitude modulation screening.
(3) The minimum dot size is too small for many printers to reproduce correctly.
(4) Since the outlets are too small, there are still some difficulties in proofing, copying, and printing.
(5) Printing plates are difficult to image and are not stable enough. As long as any change occurs in the traditional platemaking process, it will affect the final tuning of the FM plus network and reduce the reliability of screening.

3. Hybrid Screening Features

In order to make full use of the advantages of AM and FM screening to avoid the deficiencies of both, AM and FM hybrid screening technologies are now introduced. Hybrid screening is similar to FM screening in high-light areas and dark-tone areas. The level changes in the screen are represented by the degree of fineness of the same size and fine mesh points. The positions of the dots are randomly distributed and processed through special calculations so that the dots do not overlap each other and the dots do not become too large. In order to adapt to printing, another calculation method has been added, that is, using a plurality of small dots to form a larger printing dot. In the midtone region, the position of the dot is random, and at the same time, the size of the dot can be changed like the amplitude modulation and screening. Therefore, the midtone mesh has both the distribution characteristics of the FM mesh and the tone representation of the AM mesh.

Second, hybrid screening has the following characteristics:

(1) Due to the special treatment of the positions of the highlights and shadows, the particles in this part are much less compared to the FM screening. In addition, a combination of small network points is calculated to improve the reproducibility and stability of replication.

(2) In the midtone region, because of the randomness of the dot position, the color skipping of the AM screening is avoided. In this meal, since the number of intermediate tone dots is fixed, the dot density per unit area can be calculated, so that the dot density of midtones can be defined. For the printing process, conventional precision production processes and equipment can be used to achieve high-line print quality without compromising bio-efficiency.

Mixed screening technology is accompanied by the CTP technology came into being, such as FAIRDOT and screens will be reached the Canadian network, which is aimed at high-precision printing and launched the mixed screening technology for CTP. As the core of CTP technology digital proofing, it also introduced its own hybrid screening proofing technology that imitation real network technology. This hybrid screening technology can not only express the color incisively, but also show the problems in the CTP process flow at a glance. Therefore, hybrid screening will be the best choice for image reproduction in the future. Combined with thermal CTP imaging technology, it can produce clearer, more replicable dot quality.

Third, high-fidelity color suitable for high-fidelity printing

Before naming high-fidelity outlets. First understand high-fidelity printing. Since existing paper and ink cannot fully reproduce the color gamut of natural color originals, in order to improve the saturation of certain colors on prints, the pure, bright red color is printed on the basis of four colors of C, M, Y, and K. Colors such as green, blue and purple can create a more natural contrast and a fresher sense of color in printed images. This type of printing is called high-fidelity printing. For example, when printing a picture of strawberries, the red and green versions can be added, so that the red color of the strawberry fruit and the green color of the green leaves appear more pure and lifelike. The whole picture appears vivid and vivid.

The dot distribution in FM screening is irregular, and the distribution of silver salt particles in photographic negatives and photos is also irregular. As long as the dots in the FM screening are small enough, the printed matter can fully approach the original and achieve high fidelity. Since the frequency modulation screen is not limited by the shallow angle of the screen and the color reproduction range is wide, it can produce special printing that can not be achieved by conventional four-color separation, and can perform multi-color printing of four colors, thereby creating a high-fidelity printing effect. High-fidelity outlets are a new software standard for FM technology. It is a pure software approach. High-fidelity color using FM network, more than four-color color separation technology, in the color reproduction range, print density, clarity and level compared with the four-color screening technology has a significant development.

1. High-fidelity color technology development

High-fidelity color was officially used as a noun, beginning at the Seybold Symposium (Boston, USA) in the spring of 1993. At the meeting, the Davis Company opened up a gallery to show viewers proofs printed using FM technology. The proofs were called The preliminary results of the "high-fidelity color" scientific research project--printing using more than four colors for separation printing. Up to now, there are nearly 100 companies in the world participating in this research project, including most of the international companies that have a prominent position in the prepress technology field. The goal of this project is to explore issues related to a series of theories, processes, and market trends brought about by adopting advanced technologies such as FM network points and multi-color screening. At the beginning of 1994, the color separation software launched by the Computer Research Institute of Peking University could realize the seven-color separation, which was based on the frequency modulation technology and laid the foundation for high-fidelity color platemaking technology.

2. The Significance of High-fidelity Separation Technology

High-fidelity printing technology is relative to the four-color printing technology. In four-color printing, four-color inks C, M, Y, and K are used for printing. In theory, it is sufficient to use three colors of C, M, and Y inks. However, in fact, due to various technological reasons, black ink is still needed. Also, secondary colors that are superimposed by two basic colors are not satisfactory, and secondary color spot inks must also be added. Such as M, Y two ink superimposed red than the special red ink is bright. Under this theoretical premise, high-fidelity printing was produced, that is, several spot color printings were added on the basis of four-color printing in order to expand the color expression ability of prints. The conventional color separation technology divides the colors of the original into three basic colors of cyan, magenta, and yellow, and adds black to form the range of chromatograms that the print can represent. Compared to natural colors, this range (called color coverage or umbrella cover) is much smaller. In other words, the rich colors of the natural world cannot be demonstrated with only four types of inks. The use of six-color, seven-color, eight-color high-fidelity color to produce prints, one of its purposes is to expand the scope of color reproduction, more vivid reflection of nature. Because prints with more than four colors for separation printing cannot be reproduced using conventional four-color separation technology, this technology has a special place in high value-added prints.

3. High-fidelity color problem

High-fidelity color can expand the color space that can be expressed in printing, thus improving the quality of printed color reproduction. One of the problems that high-fidelity color printing solves is how to properly achieve the color of the original object in the process of color reproduction, and what colors need to be added in addition to the four basic colors in order to more perfectly reproduce the original color. In general, this question does not have the same answer, because different prints have different themes and there is a difference in the color focus that needs to be expressed. According to the deficiency of traditional four-color ink performance color gamut, a multi-color printing method was proposed. However, for common and practical process requirements, there are basic choices to meet the needs of most users. For example, the basic colors used in the Kupper and Linltype-He VCF color systems are C, M, Y, K, and Orange. Green, purple, and its characteristics are in the chromatogram in the coverage of the maximum expansion as the goal, taking into account the practical aspects of production; the latter chromatogram represents a larger range than the former, through the completion of the secondary scanning color separation. The basic colors used in the Pantone 6 color system are C, M, Y, K, blue, and green, which are characterized by the inclusion of Pantone chromatograms and reproduction as much as possible.
Ektachrome Offset Chromatography is the target for many of the 6-color presses on the market. The basic colors used by Scitex are C, M, Y, K, red, green, and blue, which are characterized by two components of seven colors resulting from two operations of an RGB scan. The basic colors used by Crosfield Hyper Color are C, M, Y, K, C, M`, and Y`, which are characterized by the use of an ordinary 4-color machine that can be printed in two separate steps. The same color ink added can make the local relative density exceed 2.2. , to achieve the expansion of the chromatographic range. But when printing, intimate friends use transparent ink. The four-color version of the traditional four-color hard to reproduce the metal color and pearl color, high-fidelity color technology can be a good reproduction.

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. Such as Hexchrome high-fidelity printing is a multi-color double-sided printing process, with single-channel, multi-color printing, high profit, high production efficiency. Japan's printing technology is known for high quality and fine prints. In the field of multi-color printing, printing equipment with eight or more colors has entered the Japanese market. Most of the formats are facing, and some even reach 10 colors and 12 colors. At the same time 8-color A2 format, 6-color A3 format printing presses have also landed on the market. In addition, five-color double-sided printing presses also appeared in commercial printing, but from the perspective of cost savings, product development will focus on web printing presses.

The use of high-fidelity printing increases the production costs and the technical requirements for the production process are also high. For example, using more plates and inks costs more than four-color printing. In addition, there are also some factors that limit high-fidelity printing to replace the traditional four-color printing, such as the widespread use of multi-color printing presses, the need to add film, version