Quality comparison between the most popular 300 sc

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Comparison of the quality of 300 line and 150 line prints

1 preface

the quality of print reproduction is mainly evaluated from the two aspects of image color reproduction and tone level reproduction. The reproduction of tone level mainly depends on the number of points in the unit area and the number of points that change 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 points 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 and 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 prints with more levels, higher definition, richer colors and reproduction effects close to the original, so as to meet people's needs for high-end album and famous product packaging

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

2 experimental analysis

as we all know, point enlargement (including mechanical point enlargement and optical point enlargement) in the printing process is an inevitable phenomenon 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 a suitable output characteristic curve before printing plate output, so that it can be called when output

The diameter of 2% point of

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

the selection of test materials is also relatively strict. We should take full account of the small printing points of 300lpi and choose 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: adopt gaobaoli Bida 74 four opening five color plus light sheet fed offset printing machine just introduced by Sino German printing training center

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

③ printing ink: CMYK ink with strong coloring power, low strength and good rheological property, which is provided free of charge by German hostmann Steinberg (affiliated to amber group)

④ fountain solution: ACE dindh2010 fountain solution (pH value controlled between 4.8~5.2) provided by VIGRA company in Germany is used

⑤ PS version: adopt the locally produced jindongyang pattern PS version

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, with a total of 8 pieces, 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 didn't 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 output 300lpi and 150lpi on the same page at the same time, we may output 300lpi and 150lpi films respectively, and then combine the page information of 300lpi and 150lpi on the same page by hand

(2) printing plate drying

before drying 300lpi point prints, we did a series of tests, including PS plate resolution and finding the right exposure time. If the resolution of PS version cannot reproduce the minimum point, it obviously cannot meet the requirements. We use ugra1982 print proofing measurement and control strip, and use the hierarchical exposure method to test the PS version of jindongyang pattern. After developing the PS plate under normal development conditions, observe the reproduction of the Yin and Yang circle lines on the ugra1982 print proofing control strip for testing 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 clearly reproduce the low noise of fatigue testing machine, 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 the method of graded exposure. In this process, we have gone through a detour. We first clean the glass on the plate printing frame 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 (without supplementary exposure process), 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 plates 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 in this way can not meet the requirements of printing, which is mainly manifested in the following aspects: the level loss of bright tones and the unacceptable dot expansion of dark tones under the effect of printing pressure. Therefore, we must shorten the exposure time of the printing plate and reduce the maximum field density of the film

according to German colleagues, 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 for test again, and then normally expose the printing plate at 250 exposure beat, 300 exposure beat and 380 exposure beat respectively (also without supplementary exposure technology). After normal development, it was found that 90% of the points on the positive plate exposed at 300 exposure beat, 380 exposure beat and 250 exposure beat were clearly visible, Only on the positive plate exposed at 250 exposure beats, 5% of the dots are still retained. Therefore, we set the printing time as 240 exposure beats

(3) 4 is to solve the development problems of different kinds of materials by classification printing process

in order to achieve the ideal printing reproduction effect, we replaced the 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. In the process of printing, Mr. Hasse impressed his Chinese counterparts with the unique persistence of Germans. He always sampled and compared carefully with the reference appearance, so as to get the best printed matter as far as possible. The printing speed reached 10000 sheets/hour at its peak

Taking high-precision grating ruler

5 result analysis

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

(1) whether there are 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't 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 the length of the dot side. The point side length of 150lpi is 167 μ m(1 × two point five four × 10000/150), that is, the diameter of rose spot at this time is 334 μ m~668 μ M, when the bright distance is very small, the rose spot will be clearly visible. When the bright distance is very large, the rose spot will be clearly visible. When the bright distance is very large, the diameter of the rose spot is within the limit of human visual resolution, and people can't see the rose spot phenomenon. The functional characteristics of the cardboard tension tester are as follows:. 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, because the point size of 300lpi printed matter is only one fourth of that of 150lpi printed matter, that is, the content originally reproduced by one point is now reproduced by four small points, resulting in the sharpness of the hierarchical boundary of the image, which correspondingly improves the sharpness of the image

(3) color softness

am plus 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 copies the color information of the four incoming pixels. In fact, in most cases, the gray scale values of these four pixels are different, but when generating points, 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 points. This is the main reason why we think that the low line print is not as soft as the original. If we use 300lpi hanging line number output, that is to say, each point copies the color information of a pixel, and the gray scale of the original can be copied one by one, and the color obtained is relatively soft and does not appear stiff

(4) hierarchical expressiveness of printed matter

the hierarchical expressiveness of printed pictures is the reproduction degree of fine levels, that is, the so-called texture. It is based on the resolution of fine levels of the original image, but it is also affected by other factors such as the number of lines added. Because when the imagesetter outputs with 150lpi number of wires, its laser accuracy 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), while when the imagesetter outputs the number of lines with 300lpi, its laser accuracy is 4800dpi (300 × 16)。 Obviously, the number of 300lpi points in the same area is 4 of 150lpi points

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