Several screening technologies of the hottest CTP

Several additive techniques of CTP

the printing reproduction process is the process of converting continuous tone images into eye tone images, and dots are the most basic elements of eye tone images. Printing reproduction is to control the ink volume through the density change of the dot area, so as to reproduce the effect of the original tone change. In the process of printing and reproduction, additive technology has always been a core technology of image and text output. Its development has experienced three stages: contact screen photographic processing, electronic scanning color separation machine electronic processing, and computer digital processing

amplitude modulation plus technology

amplitude modulation plus technology, also known as am (amplitude modulated screening) technology, is a traditional plus technology. When recording points, the direct plate making machine divides the recording plane into small squares according to certain rules, which are called recording grids, n × N recording grids form a single unit. For example, a target adjustment unit consists of 16 × If it is composed of 16 grids, the gray level of the point that the eye adjustment unit can display is 16 × 16＋1＝257。 The size of the image gray value determines the number of exposure of the recording grid in the eye adjustment unit. The ratio of the number of exposed grids to the total number of grids in the eye adjustment unit is the percentage of points at this point, as shown in Figure 1

for the direct plate making machine, the number of grids in the eye adjustment unit is variable, which is jointly determined by the output resolution of the equipment and the number of lines added. If the number of grids of the target adjustment unit is n, the resolution of the output device is dip, and the number of lines added is line/inch (LPI), the relationship between the three can be expressed by the following formula: n = (dpi/lpi) 2

it can be seen from the above formula that if the number of lines is fixed, the higher the resolution of the output device, the more the number of grids of the eye adjustment unit; With a certain resolution of the output device, the higher the number of additional lines required, the less the number of grids of the eye adjustment unit

the number of grids in the eye unit actually determines the gray level of pixels in the digital image that the point can represent. If the recording resolution of the output device is 2400dpi and the number of lines added is 150 lines/inch, the visual adjustment unit is composed of 16 × It is composed of 16 grids, which shows that it can show 256 gray levels. Plus the blank space, it can show a total of 257 gray levels. If G is used to represent the gray level, the gray level that the eye tone can represent can be expressed by the following formula: g = (dpi/lpi) 2 + 1

because the resolution of the direct plate making machine usually only provides a limited number of gears to choose from, for the same output device, the change of the number of small squares of the gray level of the eye tone is also limited

the correct use of electronic universal testing machine fixture. The image level and color composed of amplitude modulation points can generally meet the requirements. It is also a commonly used addition technology in CTP process, and it has long been used to using amplitude modulation addition in printing, but amplitude modulation addition also has its shortcomings

first of all, the fine level of the image represented by the AM plus point is mainly determined by the number of lines added, which needs to be at the expense of the accuracy of the direct plate making machine. For example, if the resolution of the direct plate making machine is 3600dpi, in order to copy 256 gray levels of the image, the resolution of the direct plate making machine needs to be reduced to (3600 ÷ 16) = 225 lines/inch at the time of output

secondly, the addition angles of the four color plates of AM addition are 90 °, 15 °, 45 ° and 75 ° respectively. When printing, small rose spots often appear in the overprint of the four plates, and the visual feeling will be more obvious once the number of lines added is low

finally, if the addition angle of the four color plates is wrong during overtime, moire will appear during printing, which will seriously affect the quality of printing

FM plus technology

FM plus technology, also known as FM (frequency modulated screening) technology, is formed by using computer technology with the cooperation of hardware and software. The frequency modulation points are randomly distributed in space, and there is no rule to follow, as shown in Figure 2

the diameter of frequency modulation point is generally 10.6 ~ 30 μ M, the size of each point is the same, and the ink volume on the paper during printing is adjusted by changing the density of points, that is, by changing the frequency of points in space

FM plus technology has two basic types: one is that the size of each point is certain, and only the spatial distribution of points changes randomly, which is called primary FM point (usually referred to as FM point); The other is that the point size and spatial distribution frequency are changing, which is called secondary frequency modulation point. Its point distribution is shown in Figure 3

FM plus technology solves many problems that are easy to occur at am points, such as there is no plus angle in various color versions, and there will be no moire and rose spots; Dots make the picture have higher resolution; The jumping phenomenon of middle tone color can be eliminated, etc

compared with am plus remember, FM plus has higher fine level expression ability under the condition of the same resolution of the output equipment, that is, it can output higher precision plates with a direct plate making machine with lower recording resolution. As shown in Table 1, under the condition of the same resolution of the output equipment, the comparison of the image accuracy of FM plus and am plus output points

although FM plus has many advantages, because the diameter of FM point is too small and the printing time point increases seriously, many printers cannot reproduce the image level correctly. In addition, the points added by FM are irregularly arranged, so lines and checkers like structures will be generated locally, the emphasis will increase rapidly, and ink accumulation will be generated locally. These are the main reasons why FM plus technology is not widely used in actual production

staccato shifangjia FM plus technology used by Cleo in its CTP technology belongs to secondary FM plus technology. Shifangjia FM plus technology provides a variety of point sizes, which point size depends on the requirements of printing. Shifangjia 10 μ M is the most delicate point, which is suitable for fine printing. Most commercial printing can use 20 μ M points, while newspaper printing is suitable for 36 μ Point of M. Shifangjiajia adopts high-frequency random dot insertion technology, which can show subtle details and improve the color fidelity of the image. After optimization, the additive structure can not only completely avoid rose spots and moire, but also make the eye tone structure more stable, reducing the accumulation of particles, dots and intermediate tone ink. The point changes of sifanga secondary frequency modulation plus and random frequency modulation plus of Cleo are shown in Figure 4

hybrid screening technology

hybrid screening technology is a CTP addition technology that draws on the characteristics of amplitude modulation and frequency modulation. It not only embodies the advantages of frequency modulation points, but also has the stability and operability of amplitude modulation points. Generally, when using amplitude modulation plus technology to produce fine prints of more than 300 lines/inch, the accuracy of the direct plate making machine should reach 4000dpi, which will reduce the output efficiency and put forward high requirements for printing management and registration. A major feature of hybrid processing is that under the condition of using the original output resolution (such as 2400dpi), it can achieve a picture accuracy of more than 300 lines/inch without affecting the output speed, and does not need the harsh conditions required by the traditional high-speed digital processing process. The printability is the same as the traditional am point, that is, under the existing printing conditions, it can truly achieve 1% - 99% point reproduction

sublima addition technology of AGFA company is a hybrid addition technology that has been successfully applied in CTP technology. As shown in Figure 5

sublima addition technology makes reasonable use of amplitude modulation and frequency modulation addition technology. High line number amplitude modulation points can be used to express the fine level of the middle tone of the image, and frequency modulation points can be used to express the level of high light and dark tone. It takes the minimum point that can be represented by printing as the dividing point, uses amplitude modulation points above the dividing point, keeps the point size unchanged below the dividing point, and changes the number of points to represent the level. The size of the dividing point varies according to the number of lines added, as shown in Table 2

sublima addition technology adopts the patented XM overclocking operation method of AGFA. When the AM point transitions to the FM point, the random point of FM continues the angle of the AM point, completely eliminating the transition trace, and allowing the points of the two frequencies to be cleverly fused, as shown in Figure 6

in addition, the calculation method of sublima plus technology can be optimized during rip, so the output efficiency is not greatly affected

sublima plus technology realizes high-speed printing without changing the existing printing conditions and increasing the cost. The print image is very delicate. The rose spots composed of dots and dots under 340 lines/inch can hardly be identified with the naked eye. They look exactly like photos, significantly improving the quality of the print. Main advantages of sublima plus Technology:

1 There is no need to change the printing conditions. Sublima plus technology is based on the design of the minimum printable points (175 lines/inch, 2% points) of the printer. The 340 lines/inch points are the same in size at 8%, 2% and 1%, and the hierarchy is expressed by reducing the density of point distribution, as shown in Figure 7

the same method is applied to 92% - 99% points. The minimum point of 340 line/inch sublima is greater than 175 line/inch and 2% am point. If the printer can copy 175 line/inch and 2% am point, 340 line/inch and 1% - 99% sublima point can be copied completely

2. No increase in printing costs. Using the existing printing equipment and technology, we can print high-speed prints, significantly improve the quality of prints without increasing costs. Sublima can add up to 340 lines/inch

3. No reduction in output efficiency. When outputting sublima points of each line number, such as 210 lines/inch, 240 lines/inch, 280 lines/inch, 340 lines/inch, etc., as long as the direct plate making machine adopts the output resolution of 2400dpi, the output efficiency will not decrease with the increase of the number of lines added

4. The image hierarchy is delicate, especially in flat areas, which will not be as rough as FM points

in addition to the sublima plus technology of Agfa, the civida plus technology of screen company is also a part of the hybrid plus technology. So do you know the function and operation steps of the zigzag experimental machine? Let's watch it with 1. The difference between shibidaga, am plus and FM plus is shown in Figure 8

shibidaga can select "similar frequency modulation points" in time according to the changes of color and level in the picture. It uses fine points of the same size in the highlight area with a point percentage of 1% - 10% and the dark area with a point percentage of 90% - 99%, like frequency modulation points, and shows the level changes of the image with the density of these points, but the size of the smallest point is larger than that usually used, thus making up for the difficulty of printing frequency modulation points. At 10% - 90% of the intermediate modulation part, the point size will be changed like the amplitude modulation point, but the positions of all points are random, which means that the addition angle does not exist. This technology enables civida to achieve ultra-fine processing quality equivalent to more than 300 lines/inch under the conventional production conditions of 2400dpi and 175 lines/inch, while avoiding the impact of rose spots and moire on the print quality