Formation of printing dots in printing manuscripts and its production mechanism

Fourth, dot shape
The dot shape is related to the visual effect when the printed matter displays different image levels, and it also has a certain influence on printability. The most common dot shapes are square dots, circular dots, and chain dots. As shown in Figure 16. Sometimes, in order to produce special visual effects, some special dots are also used, such as linear dots, cross dots, concentric circular dots, brick dots, waveform dots, oval dots, and sand-shaped dots.

Figure 16

The square dot is a traditional dot shape. The dot is a square, which reflects a strong level of ability and a rich picture tone. However, after the square network points are affected by optics and chemistry, the square corners are easily deformed; the percentage of the same outlets is longer than that of other outlets; the dot expansion rate is the highest; when the outlet coverage of the outlets is 50%, the outlets are just at an angle, and the outlets are expanded. When the dots are narrowed, the corners are disengaged, and when the signal strips detect the print quality, the dot duplication of the midtones is observed with a 50% square dot. This is very simple and straightforward, as shown in Figure 16. Based on the features of square dots for subtle levels of expression, not rich midtones, poor transition, and soft images, they are often used in image reproduction where the texture is good and the middle tone is dull.

The circular outlets are just tangent to the arc at 70%, and the outlets below 70% are all independent, and in the same percentage of outlets below 70%, the perimeter of the circular outlet is the smallest, and the outlet expansion rate is the smallest. As a result, circular dots have a unique effect on the highlights and intermediate tone levels. However, 70% or more of the circular dots are in contact with the arc, and the dot enlargement rate is high. When the signal strip detects the print quality, 75% of the square dots are used to observe the dot duplication of the dark tone, as shown in FIG. 16 . Therefore, the image of the circular dot will produce vacancies and skip levels at the 70% gradation, and the gradation level at the dark tone will be easily blurred, and the tone loss will be severe and the gradation reproducibility will be poor. Based on this, circular dots are commonly used in image dubbing in high and medium areas of the screen, duplication of requirements, and dullness in image duplication.

The chain-shaped dots are diamond-shaped, and the two diagonals of the dots are not equal. As shown in Figure 16, when the percentage of dots is 35%, the long diagonal is just at the corner and the short diagonal is disengaged; when the dot percentage is At 65%, the short diagonal was just at the corner, and it was off at the long diagonal. Therefore, in the middle tone area of ​​35% to 65%, the density of the picture has two small jumps. Unlike the square dots and circular dots, there is only a big jump of 50% and 70% respectively. Therefore, the transition of the intermediate tone density of the chain-shaped dots is very soft and rich in layers, which is particularly suitable for the copying of manuscripts of landscapes and figures, and is conducive to the reproduction of the soft tones of large-scale midtones, flowers, and leaves on the screen.

As for the brick mesh, as the name implies, it is suitable for representing buildings; concentric circles are suitable for expressing the vortex effect; the waveform mesh points are suitable for expressing the water landscape; and the linear mesh points are suitable for the performance of the trunk bamboo forest.

In print copying, selecting appropriate dot shapes based on different manuscript screens and artistic effects to be expressed will help improve the quality of print reproduction and achieve unique beauty.

Fifth, the number of outlets

The dot line number is the unit of the thickness of the dot, that is, the number of dots that can be accommodated per unit length, also known as the number of screen dots or screens, and the unit is: line/cm (l/cm) or line/inch ( l/in).

Table 1 Relationship between different products and outlets

Product Name Newspaper Posters Ordinary Print Fine Products Advanced Products Superfine Products Dots (Lines/cm) 4054607080 Number of Lines (Lines/Inch) 100133150175200



In general, the higher the number of dot lines, the larger the number of dots in a unit area, and the smaller the dot cell area. For the same dot coverage, the smaller the ink droplets, the clearer and crisper the expressed image, and the higher the picture quality. As shown in Figure 17, the left screen dot line number is larger than the right figure screen dot line number.

Figure 17

Therefore, different dot lines are selected for products of different quality requirements.

Of course, the choice of dot line number is not absolute, but also according to the use of print products, paper type, device resolution and other factors in an overall arrangement, a reasonable choice of appropriate dot line.
(to be continued)