The hottest halftone printing screening technology

Halftone printing plus technology

preface

in the history of more than 100 years of the development of modern printing industry, halftone printing plus technology has also taken a big step forward unconsciously. Am (amplitude modulation: commonly known as amplitude modulation, as shown in Figure 1) as a traditional point, the point spacing is equal, the screen angle is strictly set, and the tone reproduction is stable. However, am has well-known defects, which are easy to produce moire and sometimes have color skipping, broken lines and other phenomena. Moreover, the registration accuracy during printing is very strict. The development from am point to FM point (frequency modulation: called FM, as shown in Figure 2) has new features. FM points are of the same size and are randomly configured to show the tone in terms of the number of points per unit area. FM points do not need high registration accuracy. Due to the small dots, the re extrusion technology of details, which can be seen by suppliers in various exhibitions and rich tone performance, it is the first choice for exquisite prints. FM point solves all the problems of the above am point, but FM also has its shortcomings. First of all, because FM dot is small, its printing is much harder than am dot, and its stability is also inferior to am dot. Moreover, due to the poor uniformity of points, the tone of the image with a flat tone has an uneven feeling. So at present, am point is still the mainstream in application

on the other hand, with the advancement of plate making and printing digital process (CTP), printing technology is also improving, and the demand for fine printing of 200 ~ 300 lines has been revealed. However, the difficulties of AM point and FM point hinder the development of this technology

fairdot (Figure 3) introduced in this paper is a kind of hybrid point, which combines the advantages of AM and FM, and is also aimed at high-precision printing

different point shapes

fairdot technology can form different point structures in different tone regions

I. high light and dark areas

FM points can occur in high light and dark areas. In other words, in these two parts, the tone is expressed by the number of points with the same size and random distribution. However, although it is randomly distributed, its configuration is very optimized, and there will be no problem of excessive point space density. This also suppresses the chance of particles in the image

in addition, fairdot technology deals with the minimum point size. Generally, the minimum point that can be exposed to the printing plate in the 2400 DPI output machine is 1/2400 inch (=10.5 μ m）。 However, due to 10.5 μ M point is too small and difficult to print, which affects the stability and reproducibility of printing

fairdot is composed of one or several light points (the minimum point size of 2400 DPI output machine is expanded to 21 μ M or 32 μ m) In order to improve the stability and reproducibility (Fig. 4, 5, 6)

second, the points of middle tone

middle tone are still randomly distributed like FM, but the expression method of tone is am style (irreqular cluster dots). In other words, the intermediate tones are represented by a certain number of random points of different sizes (Fig. 7)

if you pay attention to the phenomenon of convergence, you can find that in the AM point, the points close to the middle tone are almost connected together due to the specific tone. Therefore, color skipping is easy to occur in tone output. In fairdot technology 1, torque measurement range: small range 0~50nm, large range 0~1000nm, when connecting between nearby points, each joint point is different, which prevents color skipping. Moreover, as a difference from FM, the point density (line number) of intermediate modulation can be defined. Since the number of points is fixed, the density of points can be calculated from the number of points per square inch. For example, if there are 40000 points per unit area, the density equivalent to 200 lines can be reproduced. However, this is limited to the intermediate range

so what kind of range is the so-called intermediate tone in the whole tonal region? We can know from the following calculation: with 2400 DPI output accuracy, set the minimum point size as 2 × 2 light spots, equivalent to fairdot of 400 lines = (2 × 2）÷（6 × 6) =0.111, that is, the large range of point area ratio from 11.1% to 88.9% is the middle tone area

spatial frequency characteristic analysis of 50% tone

now from another perspective, what is the spatial frequency characteristic of 50% point image? (Fig. 8) shows a circular spectrum

the center of the ring represents the low-frequency area. The closer it is to the low-frequency area, the coarser the picture is, with a sense of granularity. On the contrary, the outer ring represents the high-frequency region, and the more its components, the better the reproducibility of details, but the worse the printing stability. Features of fairdot: fine, good stability and no moire, indicating that fairdot is between low and high frequency areas. The circle radius in Figure 8 represents the point density (number of lines)

point density comparison

Figure 9 shows am (175 lines), FM (21 μ m) And fairdot point density (concept map). The horizontal axis represents the area ratio of points, and the vertical axis represents the density of points. From this figure, we can see that fairdot combines the properties of AM and FM

the most suitable printed matter

as mentioned above, fairdot is a solution for high-precision printing. In particular:

● the performance of design drawings such as maps, rooms and details such as hair

● the reproduction of fine patterns such as lattice and wood grain of stereo microphones and fashion cloth

● the reproduction of commodities with black (dark) as the keynote

● the reproduction of smooth tones such as shadows and CG

● the reproduction of fabric stripes and CTR images can play a very good effect

on the other hand, usually when making fine printing with more than 300 lines, the accuracy of the output equipment is required to reach 4000 DPI, but in this way, it will inevitably reduce the degradation time of ordinary plastic bags, which requires more than 100 years, and the requirements of printing management and registration are very high. Another major feature of fairdot is that it can output the number of high-speed lines with the original management level on a low resolution, such as a 2400 DPI output machine, while maintaining the same production efficiency

printing test

then, what is the stability of using fairdot technology for high-precision printing on the original equipment? This requires actual printing tests. After the trial printing of AM (175 line) and am (300 line), the results of image quality and printing stability are as follows:

Image

moire occurs in the lines of AM (175 line) clothing, so the reproduction of details is not very good. In fairdot technology, all the above-mentioned defects have not occurred at all. Therefore, the fine texture of wood grain furniture and cloth grain, as well as the lines of hair and lines, etc. are reproduced very well. Using am to print 4-color maps, indicating that the disconnection of roads, routes, etc. is quite significant, and there are also many. But the lines of these prints represented by fairdot technology are quite smooth

therefore, the same printing quality as am point can be obtained

stability

test and evaluate the image point area ratio of highlight, intermediate tone and dark tone for every 500 copies. The order of evaluation is am (175 lines)> recovery of FAI international market rdot> am (300 lines). The stability of highlight part is better than that of AM (300 line), because fairdot dot dot is easier to print

however, the greater the dot density, the more vulnerable it is to the influence of wetting water volume and ink emulsification, so its stability is slightly less than that of AM (line 175). If you pay a little attention, there should be no problem

the above tests have proved that the general equipment (= maintain productivity), using fairdot technology, can completely carry out high-precision printing. (translated by Hong Shenwei)