The cause and solution of the hottest net point mo

The reason and solution of Moire dot (I)

the editor press that taking advantage of the first Asia Pacific printing exhibition, the China printing and image making Association specially invited the international printing and image making Association (SGIA), the Federation of European printing and image making associations (fespa) and the Asia Pacific printing and image making Association (asga) to jointly hold the Beijing New Era Jiyin forum. The speech of the forum not only described in detail the technical points of silk printing color reproduction process, but also talked about the impact of current digital technology on silk printing. It also provided information about Lin Guang in China's printing industry market. It integrates professionalism, technology and information, and was welcomed by participants at home and abroad. With the consent of the speaker, these speeches will be published successively in the "printing forum" column of silk printing magazine from this issue to feed readers. No reprint without permission. Among all the challenges encountered in color tone printing, moire is probably the most destructive and difficult to deal with. The most prominent problem is that it seems completely unpredictable, and its emergence and disappearance are random. Through the practice and observation in the past 15 years, several reasons for this phenomenon are summarized. Before we discuss the causes and types of moire, you should have 2 ~ 3 sets of different detection devices. At least there should be a 10 times small color correction magnifying glass and a 25 ~ 30 times portable microscope. In addition, it is recommended to prepare a 100x microscope. The thinner the printed dot, the higher the magnification required during detection. Without these detection equipment, the specific situation of the point cannot be observed. For us, moire is often the most destructive to the pattern. It can be banded, linear, checkerboard, gem shaped or cause tone deviation. It may spread over the whole pattern, or it may be concentrated in a specific area. We really need to know about moire and learn how to avoid or reduce it. Here, I want to say that moire can't be completely controlled. No matter how careful we are, the key is that there are too many factors that may cause moire. We say that moire phenomenon is challenging because some factors that lead to moire are beyond our control. Almost all aspects of silk printing are included. The finer the dot, the more difficult it is to control the electric grain. Therefore, we must strictly follow some relevant suggestions for the eye tone of special fine sleeves (100 threads/inch or more than 40 threads/cm). Moire can appear in several different stages, including: 1. The process from manuscript to film (manuscript to film); 2. Type of digital film point (film to film and film to version); 3. Film angle (film to film); 4. Eye adjustment and silk (film to version); 5. Film angle and wire angle (film to version); 6. Image and substrate surface (plate to substrate); 7. Ink granularity and substrate (the refinement of products is the driving force to promote its industrial development from ink to substrate); 8. Printing ink layer (ink to ink). Moire may appear at every step of the printing process. In order to reduce the appearance of moire, our operation must be well systematic. Reducing variable factors and standardizing operation methods are crucial to our success. If you don't follow this principle, moire may appear and disappear at any time. It can cause great damage and even bring disastrous consequences to our production. The most likely thing to appear at the beginning is the manuscript itself. In our environment, moire will appear naturally. There are also some physical originals that produce moire patterns once they are photographed. For example, there are regular patterns on the physical originals. Silk texture, wicker chair, fence, screen, shutter fan, floor pattern and any similar material showing repetitive surface texture. Providing printed posters or other similar printed materials to the printing factory by customers is another main reason for the turtle grade of the original, because the original itself has been equipped with the dot graphics generated by the previous printing. To reduce this situation, it is recommended to order 4-inch x King inch duplicate film, and then use transparent film for color separation. In the production process, the dots have been fine enough to fuse into one dot. At this time, there is no moire formation between dots in color separation. At present, many scanning software also has the function of deleting moire to reduce the printing texture. When using a laser scanner or Phototypesetter for film production, special attention should be paid to the resolution. The output resolution of the first generation laser scanners (DS, hall, crossfield) is not particularly high. The electron generation point (EDG) capability is still primitive. During the manufacturing process, due to a series of intermittent approximate apertures generated by the laser, the thinner the points in the highlight area, the more irregular the edge will be. It can be said that the finer the point is, the rougher the edge is, and the resulting point is often star shaped or other irregular shape. It is indeed a problem for those printing houses that directly purchase large format, because the film is made according to a high number of lines (150 ~ 425), and then enlarged to the final number of lines, all these irregular things also appear. The latest scanners and imagesetters have overcome this situation. Before purchasing the film from the color separator, you should take samples and carefully observe whether the edge of the point is clear under the magnifying glass. The second main reason for turtle effect is the angle between them. In order to reduce the turtle effect between points, the three dark colors (magenta, cyan and black) are 30 ° to each other. Because the Yellow contrast is not very strong, clamp it at the position of 15 °. The standard lithography angles are: Yellow 0 °, 90 °, magenta 15 °, cyan 75 °, black 45 °. The difficulty lies in that 0 °, 90 ° and 45 ° are the main moire formation angles. This is because the direction of the point is consistent with that of the line, resulting in the line completely blocking the whole row of points. At 45 °, the intersection of lines will block the point. This means that moire patterns almost always appear in eye tone images made from these angles. Therefore, if the purchased color separations are separated according to the angle of lithography, it can be said to be asking for trouble. For the ratio of wire mesh to dot, the smaller the dot, the more important the ratio is. The higher the ratio of mesh to dot, the less important it is. For any case lower than 4.o:1 (the number of wire mesh is higher than the number of wires added), we need to change the basic angle during color separation. The acceptable angle is to rotate all the plus angles ± 4 ~ 8 °. This can rotate the original along the horizontal line during color separation, or rotate the angle during scanning. The first method is less used, because the current scanner department can provide several sets of scanning angles. The second method is to ask the scanner to make some settings and adjustments. In practice, some scanners cannot complete this work, so the first method needs to be adopted. Before determining the rotation angle, be sure to consult your service provider. In addition, the rotation of the angle can make the Phototypesetter reset the grid image processor (RIP), which they are usually unwilling to do. You must check the received film carefully to ensure that it is the angle you require. There is a third way to solve this problem. Put the silk on the frame according to the offset angle. There are several reasons why I disagree with this method. First of all, it is difficult to accurately position the wire at 4 ° to the frame. Secondly, when you are doing oblique stretching and sticking, the tension of the wire is inconsistent with the force of the scraper. In this case, I can't believe how stable the version tension is. But my intuition tells me that when the silk thread forms a line with the direction of the force, it is difficult for us to ensure the stability of the tension. If you use an adjustable frame, this becomes more important when the thread tension deviates from the thread direction. Coupled with the function of the scraper, it will become more difficult and cause greater deformation. Moire caused by angular interference usually presents regular moire bands. When the ratio of mesh to dot is high, moire bands will appear in the highlight area first. As the ratio of mesh to dot decreases, moire will spread to all hue areas. If the ratio is higher than 5.0:1, angular wrinkles basically do not exist. The next reason for turtle effect is the relationship between the number of silk meshes and points. Simply put, it is the ratio of the number of wire mesh to the point, that is, the number of wire mesh/the number of wires = the ratio of the number of wire mesh to the point. In this regard, there were many reference ratios in the past. The most common is that the minimum ratio is not less than 3.5:1. Although I agree with this view, there are still many problems worthy of our attention. Note that moire is formed by overlapping textures. When moire appears, what we can see with our naked eyes is that the printing points are uneven. Some are round, some are half sided, and some are even lost. The higher the ratio of wire mesh to dot, the less chance the dot will be distorted during printing. For example, if the ratio is 3:l, the point can easily change from the original round point to square point. Once the rows of points deform more, our naked eyes will feel the moire. In order to reduce repetition, two points are necessary. First, try to use a higher ratio as much as possible. As long as the ratio is higher than 5.0, it will certainly achieve good results. Secondly, if the ratio is lower than 5.0, the first digit after the decimal point should be avoided to be even, and it would be better to ensure that the single digit and hundred digit after the decimal point are odd (such as 3.55). It should be realized that when the ratio is odd, we can disperse the stable texture and load it under heavy load, so that the naked eye cannot detect the change of texture. We must ensure that when the silk thread interferes with the point and blocks the opening, the interference at each row of points is different, and as a result, rows of different but not repeated points are obtained. In this way, even if the points in each row are different, we won't look moire with our eyes. In addition, we should also pay attention to the relationship between the number of wires and points. The number of silk meshes marked may not be its actual number of silk meshes. All silk is woven according to measurement standards, such as how many meshes per centimeter. In countries with English system, we usually divide the number of centimeters by 2.54 to convert it into inches. In this way, in most cases, the obtained silk day value is a divisor, with a difference of about 5 mesh. A best example is that 150 mesh/cm is 390 mesh/inch after being converted into English system. In fact, the actual value after conversion should be 381. At the same time, we should also understand that the number of mesh marked is the number of mesh without tension. With the increase of tension, the number of wire mesh will decrease. If you don't use the wire mesh measuring instrument, you can't know its effective mesh number, which we absolutely can't ignore. As the tension continues to increase, the effective mesh of silk will continue to change. When we are discussing silk, we should see the reality that the mesh number of silk is not accurate. When knitting silk, the warp is first fixed to the knitting machine, so the number of warp is fixed. Generally speaking, the measured value of the longitude of silk is relatively accurate. The weft line is not very certain. It is very common to have ± 5 fluctuations on the basis of the number of targets, and it has high compatibility with organisms. The error range of the number of wire mesh I saw is more severe than ± 5, which is one of the reasons for local moire, which is beyond our control. The number of weft threads is not invariable in the printing process, so our ratio of mesh to dot also changes constantly within a certain range. There is another key point about the relationship between the number of wire meshes and points. The ratio is based on the number of lines selected