Introduction to digital screening technology in th

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The whole strategy of digital addition technology in gravure printing (1)

in ordinary printing, dots are the basic unit that represents the image level and the color level of color image, and the difference of dot coverage can produce the change of color level. After more than 100 years of practice and improvement, the processing technology has developed from photographic processing, electronic processing to digital processing, providing us with a method of forming points by physical (6) steel bar pneumatic welding. Computer digital addition is a technology widely used in the high-end connection system of Phototypesetter and electric extension. The technology and principle of electric extension plus and computer digital plus are the same, but the implementation methods are different. Now, with the continuous improvement of the quality and speed of color desktop publishing system, especially the improvement of the performance of raster image processor (RIP) in key parts, the speed and quality of acceleration have been greatly improved. Compared with other addition technologies, digital addition technology shows its advantages in many aspects. It can achieve algorithms that are difficult or impossible to achieve in analog addition, and can obtain higher quality eye-catching images. Digital addition technology has become an indispensable part of image pre press processing

characteristics of digital addition

digital addition is an addition technology used in computer publishing system. According to the distribution status of the recording points, there are amplitude modulation, frequency modulation and mixed amplitude modulation/frequency modulation methods for digital addition. Amplitude modulation plus (point aggregation jitter technology) is to segment the image with invisible cells arranged in rows and columns. Each cell generates points with different areas according to a certain angle and the number of lines added. After nearly 100 years of development and improvement, the AM plus technology has been used in many printing units. In the AM plus method, the hanging method used by the electronic color separation machine is generally the is point technology (non physical and chemical tangent point) and RT point technology (physical and chemical tangent point) developed by German hell company. Postscript plus technology is used in the color desktop publishing system. Although the AM plus technology is relatively mature, there are some unavoidable defects. For example, the loss of details, the generation of moire and rose spots, visual collision, especially moire, rose spots and step jump (that is, the level jump before and after the point starts to overlap) are unavoidable in amplitude modulation, which has always affected the printing quality of the image

FM addition (dot discrete state jitter technique) is a random addition, which obtains discrete distribution of recording points. It can better avoid the defects of amplitude modulation plus technology. FM plus image has high information capacity. Frequency modulation points include primary frequency modulation points (indicating that the size (area) of each point is certain, and only the spatial distribution of the points changes randomly) and secondary frequency modulation points (indicating that the size of the point gives full play to the efficiency (area) of the measured data and the spatial distribution frequency is changing). Because the frequency modulation plus technology has no frequency interference, it is not limited by the screen angle and has no angle, so it will not form moire and rose spots, and will not produce errors; And the use of low resolution imagesetter can also obtain high-quality images and improve the output quality of film; Improve the clarity and stability of prints; In the middle tone, there is no problem of density jump caused by point connection, that is, the step jump of the middle tone is eliminated, and the tone is excessively natural and harmonious. Make the color printed matter more detailed and the printing effect better. However, FM plus also has some defects. For example, because the point size is equal and the random noise of FM plus cannot be filtered out, it has a rough and grainy feeling, especially at the high-profile level and the step of about 25%; Because the perimeter of the point is much longer than the amplitude modulation point, the point is also expanded, which requires high-precision and harsh process control and monitoring technology; The image with poor color separation effect is difficult to improve the quality through ink adjustment on the printing machine; The smallest micro dot size is too small, which makes many printing machines unable to reproduce correctly; The stability and reliability of the point are not ideal

AM/FM hybrid addition (micro gathering point technology) is an addition technology combining the advantages of AM and FM for high-precision printing. In the highlight area and dark area, it is like amplitude modulation plus, through the density of fine dots of the same size to show the hierarchical changes in the picture. The positions of the points are randomly distributed and specially calculated so that the points do not overlap each other and the spacing is not too large. In order to adapt to printing, another calculation method is added, that is, using multiple small points to form a larger printing point. In the intermediate adjustment area, the zigzag test, as one of the important inspection steps in stainless steel manufacturing, provides an important basis for ensuring the bending resistance of stainless steel materials. The position of the point is random, and the size of the point can also be changed like amplitude modulation plus. Therefore, the points in the middle part have both the distribution characteristics of AM points and the step expression method of FM points

mixing is added in the high light and dark areas. Due to the special treatment of the point position, the relative adjustment frequency of the fast oil drainage particles is reduced a lot. The fine points are combined to improve the reproducibility and stability of replication. For the intermediate tone region, the color hopping phenomenon in am is avoided because of the randomness of the point position. Since the number of intermediate adjustment points is fixed, the point density per unit area can be calculated, so the point density of intermediate adjustment can be defined. For the printing process, the production process and equipment with conventional accuracy can be adopted to realize the printing quality of high-line points, while the production efficiency is not affected

hybrid addition can be roughly divided into two types. One is to use the traditional am addition directly in the middle tone, while the full FM addition is used in the highlights and darkens. That is, the true am is used completely in the middle part, while the true FM is used completely in the highlight and dark parts. Although the algorithms of FM plus and am plus are relatively mature at present, how to make a smooth transition between these two essentially different plus algorithms is the purpose and problem of this hybrid plus

the other is to use both FM and am feature algorithms to add. At present, the transition between FM plus and am plus is mainly realized by these two methods. At present, there are mainly the following kinds of mature hybrid digital addition. (1) Samba screen and hybrid screen. Samba screen launched by Barco and hybrid screen developed by PPC are the latest addition methods specially used in flexo printing. Samba adopts FM frequency modulation for the highlight and dark parts, while the traditional am amplitude modulation is used for the middle part. The smooth transition from random point to traditional point (5% - 10%, from 90% - 95%) is automatically calculated digitally, rather than simply the interpolation mixing of their respective densities. Hybrid addition is the addition that FM and am coincide and are used in the whole density range. (2) Spekta plus. It is the new hybrid processing technology recently introduced by screen company. Spekta effectively combines the advantages of FM and am processing methods in point composition, color mixing, moire and easy operation compensation on the printer, so that its thermal CTP imager can obtain the best quality. (3) Sambaflex plus. Its characteristic is that in the range of intermediate tone, the point realizes the transition between the two kinds of addition by gradually increasing the amplitude modulation plus feature and gradually reducing the frequency modulation plus feature. In the transition region, it also performs amplitude modulation plus first, and then deletes a certain number of points from the amplitude modulation plus according to the percentage of points. But at the same time, the point will be offset at the center point. (4) Staccato plus. It is a new digital hybrid addition of the square laser spot technology staccato of Cleo at present, which is closer to the FM addition than the shibida. It can produce high fidelity images and reproduce better details without moire caused by amplitude modulation

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