When a similar halftone screen pattern is overprinted, the direction of the pattern is critical. If the direction is not correct, it will result in a disturbing pattern called "rhizard." This pattern changes with the number of dichroic sheets and the angle between the screen lines. In monochrome halftone printing, the direction of the screen pattern is generally 45°, because at other angles, especially 0 ° or 90 °, even if the number of screen lines exceeds the limit at which the eye can resolve a single point, the eye can see the line of dots and see the line pattern. However, if you prepare color separation images for four-color overprinting, you need to specify the screening angle for each main color image. The reason for this is that when several halftones (or colors) are superimposed, the moiré appears in the job, and the two-color, three-color, and four-color printings produce moire, even in black-and-white printing if the original is laced or herringbone. Patterns, screen images, or textiles also show moire patterns.
Since the moiré is caused by the improperly superimposed direction of the screen pattern, moire can also be reduced by using the angle between the screen patterns as a method for determining the halftone direction. When the angle between the screens is 45°, the moire pattern is the smallest, and the moire pattern formed when the screen angle is 30° is not significantly different from that formed at 45°. Therefore, the 30° angle allows the moiré produced by three colors to be overprinted to be minimal. However, there are serious problems with four-color printing.
Use different dot shapes in halftones to produce special effects. There are round, square, oval, two-point and three-point screens or dots, the most commonly used are round dots and square dots. When screens with these dot patterns are used, rotating them by 90° will take care of the angle pattern: 105° and 15° are the same, 0° and 90° are the same, and 45° and 135° are the same. Therefore, there are only 3 kinds of angles that can guarantee the smallest moire, the darkest color, ie black (K) is usually printed with 45°, magenta (M) with 45°, cyan (C) with 75° or 105°. The question is what angle Huang chooses. Usually yellow is used or 90°, between the magenta and the blue, because it is a pale color, and the moire between yellow, magenta, and blue is not very obvious. It is very important for high-quality color reproduction to increase the accuracy of the screening angle as much as possible. Inaccuracies such as a screen angle of 0.1° or slight overprint of two colors can cause serious moiré patterns in three or four color overprint areas.
When the difference in the mesh angle between the two colors is unlikely to be 30°, the moire pattern becomes smaller and less noticeable as the angle difference increases, and orange is likely to occur when the angle difference between yellow and magenta and cyan is 15°. , red and green obvious moire. In topics where orange or brown (eg skin tone) is prominent, magenta is usually 45° and black is 15°; when green is the main color and red is the secondary color, blue is 45°, and black is 75. °. When the 30° web angle difference requirement cannot be satisfied, the moiré can also be reduced by using halftones of different screen lines. The halftones of black, magenta and cyan in magazine printing use 133 lines/in, and the screen lines used in yellow are 120 lines/in or 150 lines/in.
In order to reduce the moiré produced by mutual interference when the dot pattern is superimposed, the traditional photoengraving technique has concluded a set of optimal screening angle combinations through long-term practice, namely, yellow version calculation, cyan version 15°, and black version. 45° and magenta version 75°. See Table 5-4-2 below.
Table 5-4-2 Traditional Screen Angle
Green 15.000° 133.000 Yellow 0.000° 133.000
Magenta 75.000° 133.000 Black 45.000° 133.000
When the Postscript page description language first appeared, there was only one screening method, namely RT Screening. It is a screening method used since the introduction of RIPI in 1985. Rational tangent (RT) screening technology is the patented technology of Haier Company and is recognized throughout the industry. One of the characteristics of rational tangent screening technology is that the 15° and 75° angles cannot be very accurate. In addition, in a set of color separation films, the number of screen lines between different colors may be different, which is not important in black and white jobs, but for color jobs it means that when the angles are close, the moire problem still remains. Very serious.
Adobe's precision screening method allows the half-tone screen to achieve ±0.001° of angular accuracy, which is related to the required screen angle and frequency accuracy, device resolution, and memory required by the algorithm.
In rational tangent screening, only the angle based on the rational tangent value can be obtained. The amount of computation required to generate a required angle of dots is large. This requires that a plurality of dots be grouped together into a unit as a pattern element, and these elements are repeated to obtain the entire image if no adjustment is made according to the imaging resolution of the output device. Screen angle will produce moire after overprinting.
The high-end color prepress market has begun to use Irrational Tangent Screening technology. The position of each network in the technology is adjusted together with its surrounding network points. This is accomplished through special hardware screening calculation logic, and the screening angle close to that of traditional photography can be obtained.
There are two other factors that can affect the quality of color halftone printing: one is the color shift caused by the screen angle (already mentioned), and the other depends on the order of ink overprinting in the printing. Both are related to less than ideal light absorption and reflection properties of the primary ink. This makes the appearance of the print product dependent on the printing method.
The following table shows the typical screen angles and line numbers of selected Postscript graphic recorders (normal number of screen lines is 150 lines/in):
OptronlcsColorSetter
(irrational tangent) 0. 00°
18.43°
45.00°
Optional network / black version
71.57° 150.00
158.25
141.00
212.00
158.25
Linuo 330 or 300 type
NeptuneRIP (2540dpi)
(rational tangent) 0. 00°
18.43°
45.00°
71.57° 141.11
133.87
149.67
133.87
Agfa Selectset5000
AtlasRIP (2400dpi)
(rational tangent) 0.00°
18.43°
45.00°
71.57° 150.00
126.50
169.71
126.50
Agfa Seleetset5000
StarRIP (2400dpi)
(rational tangent) 0.00°
14.93°
45.00°
75.07° 150.00
154.60
154.28
154.60
Source of information: pack.cn
50X200mm 3D Wire Mesh Fence is also known as 3D bending fence curvy welded fencing, triangle mesh fence,, etc. Triangle bend fence is pretty light yet durable
Wire mesh fence is a type of fencing made from wire mesh that is commonly used for security and containment purposes. It is made up of a series of wires that are woven or welded together to create a mesh pattern.
Wire mesh fence is often used for perimeter security, as it provides a strong barrier that is difficult to climb or cut through. It is also commonly used for animal containment, such as in agricultural settings. Wire mesh fence can be installed in a variety of configurations, including as a standalone fence or as a component of a larger security system.
3D-2X8 Open Mesh Wire Fence,Open Mesh Wire Fence,Open Wire Fencing,Open Wire Fence
HEBEI DOUDOU METAL FENCE PRODUCTS CO.,LTD. , https://www.doudoufencing.com