Comparison between the most popular 300 screen cab

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Comparison of 300 line and 150 line printing

1 preface

the quality of printing reproduction is mainly evaluated from the two aspects of image color reproduction and gradation reproduction. The reproduction of gradation level mainly depends on the number of points in the unit area and the number of points changing continuously from small to large. The more points in the unit area, the more points in the reproduction area, the higher the clarity of the reproduction print, the richer the level and the more realistic the color; The more the number of point changes, the stronger the level expressiveness of the printed matter, and the more delicate it looks. In the process of printing production, people control the number of points per unit area by changing the number of lines. The higher the number of lines, the more points per unit area, and the smaller the size of the reproduced points. At present, the number of lines added to coated paper is between 150~175lpi. However, with the continuous improvement of people's appreciation level, this kind of precision print can no longer meet people's visual needs. Therefore, more and more printing enterprises use high-speed wire technology to obtain printed matter with more levels, higher definition, richer colors and similar reproduction effect to the original, so as to meet people's needs for high-end picture books and famous product packaging

as a challenge, Hedu is one of the important contents of the printing seminar and gaobao equipment exhibition held by Sino German printing training center and German gaobao company in Hefei. It is to carry out the printing test of 300 line prints. With the help of technical personnel of gaobao company, we have completed the printing contrast test of 300lpi and 150lpi printing

2 experimental analysis

it is well known that point enlargement (including mechanical point enlargement and optical point enlargement) in the printing process is an inevitable phenomenon in the printing method of image transfer through pressure. The size of the point enlargement value is usually proportional to the sum of the perimeter of the points in the unit area. For the same point value, the total point perimeter of 300lpi is larger than that of 150lpi, that is, the point expansion rate of 300lpi is larger than that of 150lpi. In view of this, we should test and make appropriate output characteristic curve before printing plate output, so that it can be called during output

300lpi 2% point diameter is about 11.6 μ m. It is almost the same as the diameter of the dust particles, so the dust falling on the glass or film of the plate printing frame can easily be exposed to the sun, forming the so-called "false spots" and interfering with the normal printing. Therefore, we should strictly ensure that there is no dust in the PS plate drying process. In addition, the PS version developer shall be used to develop the PS version, and the development process shall be stable

the selection of test materials is also strict. We should take full account of the small printing spots of 300lpi and select appropriate printing materials

in the printing process, the printing workers are required to have a good professional level and good professionalism, to achieve "three diligence", and to maintain a good balance of ink and water in the printing process

3 test equipment and test materials

① printing equipment: gaobaoli Bida 74 four-way five color and polished sheet fed offset printing machine just introduced by Sino German printing training center is adopted

② paper: Korean Hansen 157g/m2 coated paper with high smoothness and good absorption is adopted

③ printing ink: CMYK ink with strong coloring power, low strength and good rheological property provided by German hostmann teinberg (affiliated to amber group) is adopted

④ fountain solution: ace

dindh2010 fountain solution (pH value controlled between 4.8~5.2) provided by German VIGRA company free of charge is used

⑤ PS version: the PS version of jindongyang pattern produced locally is adopted

⑥ blanket: special blanket provided by gaobao company shall be used

⑦ lining: special polyester sheet base with smooth surface, flat and uniform thickness provided by Gao company is adopted

4 test process

(1) original production

we use the digital originals provided by German gaobao company. These digital originals are stored on the CD in EPS format. There are 8 in total, and the data volume of each image is 83MB. We selected three representative images as the test manuscript, including skin color image, wine set image and furniture image. We did not do any processing to the originals. We imported them directly into PageMaker for edition, then called the specific output characteristic curve in the delta workstation, and finally output the film on the Hercules imagesetter. Since the Phototypesetter cannot achieve 300, and various industries are discussing how to output the topic of transformation and upgrading LPI and 150lpi on the same page, we may output 300lpi and 150lpi films respectively, and then use the method of manual composition to combine the page information of 300lpi and 150lpi on the same page

(2) printing plate drying

before drying 300lpi point prints, we did a series of tests, including PS plate resolution and finding the appropriate exposure time. If the resolution of PS version cannot reproduce the minimum point, it obviously cannot meet the requirements. We use ugra1982 print proofing control strip, and use the hierarchical exposure method to test the PS version of jindongyang pattern. After the PS plate is developed under normal development conditions, observe the reproduction of the Yin and Yang circle lines on the ugra1982 print proofing control strip used to test the angular analysis force of the PS plate (subject to the clear reproduction of at least 505), and judge that the resolution force of the PS plate is 6 μ m。 According to the calculation, the diameter of 100% points on 300lpi printed matter is 83 μ m. 2% of the points have a diameter of 11.6 μ m. It can be said that the PS version fully meets the test requirements

let's find the right exposure time. Here, we mainly consider the drying of 300lpi line. If the 2% and 98% points of 300lpi line can be clearly reproduced, the 2% and 98% points of 150lpi line must also be clearly reproduced. We also use ugra1982 print proofing control strip to find the appropriate exposure time through graded exposure. In this process, we went through a detour. We first clean the glass on the plate printing rack with glass, wipe the 300lpi signal strip film with alcohol (the maximum field density of the signal strip measured by the transmission densitometer is 5.6) and clean the PS plate with clean gauze, and then normally expose the printing plate at 450 exposure beat, 380 exposure beat and 315 exposure beat respectively (no supplementary exposure process is used), After normal development, it is found that more than 90% of the dots on the positive plate exposed at 450 exposure beats are dead, and less than 10% of the dots have been lost; On the positive plate exposed at 380 exposure beat and 315 exposure beat, more than 80% of the dots are stuck and less than 5% of the dots are lost. Obviously, the printing plate made by such drying can not meet the printing requirements, which is mainly reflected in the following aspects: the bright tone appears, the solar car runs fast and loses, and the dark tone will appear unacceptable dot expansion under the printing pressure. Therefore, we must shorten the exposure time of the printing plate and reduce the maximum field density of the film

according to the German colleague, as long as the maximum field density of the original film is above 2.4, the original top point can be completely transferred to the PS version. Therefore, we changed the output characteristic curve, set the maximum field density to 3.4, output the 300lpi signal strip film used for testing when selecting to test the fatigue life of the spring, and then normally expose the printing plate at 250 exposure beat, 300 exposure beat and 380 exposure beat (also without supplementary exposure process). After normal development, it is found that: at 300 exposure beat, 380 exposure beat 90% of the points on the positive plate exposed at 250 exposure beat are clearly visible, while only 5% of the points on the positive plate exposed at 250 exposure beat are still retained. Therefore, we set the printing time as 240 exposure beats

(3) printing process

in order to achieve the ideal printing reproduction effect, we replaced new air cushion blanket and special liner with good transmission performance before printing. The specific printing operation was jointly completed by Mr. Hasse, an experienced printing technician of German gaobao company, and the young backbone of the Sino German printing training center. During the printing process, Mr. Hasse impressed his Chinese counterparts with the unique persistence of the Germans. He always took samples and carefully compared them with reference patterns, so as to obtain the most ideal printed matter as far as possible. The printing speed reached 10000 sheets/hour at its highest

5 result analysis

by observing the contrast images after printing, we found that the difference between 300lpi printed matter and 150lpi printed matter is still very obvious, mainly in the following aspects

(1) presence or absence of rose spots

when we look at the printed matter closely, we find that the bright and middle tone areas of the image with 150lpi lines show rose spots that can be easily distinguished by human eyes, making the printed matter look very rough and the color lacks luster, while the rose spots can not be seen on the printed matter with 300lpi. This kind of rose spot is caused by the overprint of multiple dot inks, and its diameter is usually 2~4 times of the dot side length. The point side length of 150lpi is 167 μ m(1 × two point five four × 10000/150), i.e. the diameter of rosette is 334 μ m~668 μ M. when the visual distance is very small, the rose spot will be clearly visible. When the visual distance is very large, the rose spot will be clearly visible. When the visual distance is very large, the diameter of the rose spot is within the limit of human visual resolution, and people can not see the rose spot. The point side length of 300lpi is 83 μ m. Accordingly, the diameter of rosette was reduced to 167 μ m~334 μ m. Because of its small diameter, we can't see the phenomenon of rose spots even when the distance is very small

(2) sharpness of printed matter

the image sharpness of 300lpi printed matter is significantly better than that of 150lpi printed matter. The reason is that the point size of 300lpi printed matter is only one fourth of that of 150lpi printed matter. That is to say, the content originally reproduced by one point is now reproduced by four small points, resulting in enhanced sharpness of image hierarchy boundary and correspondingly improved image sharpness

(3) color softness

am process reproduces the level change and color depth change of the original through point size change. In the current field of color printing, we often scan the original with a scanning resolution of 300lpi, and then output it on the imagesetter with a hanging number of 150lpi. In other words, the first point duplicates the color information of the four incoming pixels. In fact, in most cases, the gray scale values of the four pixels are different, but the computer will ignore the differences between the gray scales of the four pixels and take the average gray scale value of the four pixels as the gray value of the point. This is the main reason why we think that the low line print is not as soft as the original. If we use 300lpi to output the number of hanging lines, that is to say, each point copies the color information of one pixel, and the gray scale of the original can be copied one by one, and the resulting color is relatively soft and does not appear stiff

(4) the hierarchical expressiveness of printed matter

the hierarchical expressiveness of the printed picture is the reproduction degree of the subtle level, that is, the so-called texture, which is based on the resolution of the subtle level of the original image, but is affected by other factors such as the number of lines added. Because when the Phototypesetter outputs the number of lines with 150lpi, its laser precision is 2400dpi (150 × 16, where herbal medicine 50 represents the number of lines added, and 16 represents the arithmetic square root of gray scale 256). When the imagesetter outputs the number of lines hanging at 300lpi, its laser accuracy is 4800dpi (300 × 16)。 Obviously, the number of 300lpi points in the same area is 4 times that of 150lpi points, and a single 300lpi

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