Copy use of different types of products - special examples of screening technology

Screening technology is the basic way to reproduce continuous tone images and is an important technology that determines the quality of printed matter. It has been in the printing field for more than 100 years and has experienced glass screens, contact screens, and electronic screening. Digital screening and other development stages, and the formation of rational screening, unreasonable screening, super cell structure screening and FM screening and other technologies. At present, AM screening and FM screening have been playing a leading role as the two mainstream screening technologies. With the development and advancement of science and technology, some special screening technologies have emerged, and they have been used in some printing fields to reproduce printed materials with different uses. This article will introduce these special screening technologies.

Hybrid Screening Technology

As we all know, AM screening is to reconstruct the tone and gradation of an image by changing the dot size by fixing the dot spacing, which has obvious advantages for the restoration of intermediate tone. FM screening is to reconstruct the tone and gradation of an image by fixing the dot size and changing the dot spacing to restore the details of the image. Hybrid screening technology is a new type of screening technology developed by combining the advantages of AM screening and FM screening.

Hybrid screening is developed based on digital screening principle and computer control technology. The principle is to generate FM network points in the high-profile and dark tone parts of the image, while the intermediate tone part simulates the configuration of the AM network point, that is, maintain a certain network point. At the same time, the tone reproduction is achieved by changing the size of a single dot. Hybrid screening technology fully utilizes the advantages of FM screening, and maintains good printability of AM sites. Therefore, hybrid screening technology can achieve good image reproduction.

The network points generated by the hybrid screening technology use the amplitude modulation network points as the skeleton, and the FM network points as the modifications. The shape of the network points is different, the positions are randomly distributed, and both the amplitude modulation and the frequency modulation network characteristics. The advantage of hybrid screening is that there is no problem with the dot angle and direction, and the low frequency component is reduced to reduce the graininess of the picture, and the high frequency component is reduced to improve the printing stability. Therefore, the printability of the hybrid outlets is better than that of the AM and FM outlets.
Art screening technology

The basic principle of art screening technology is to use various shapes of graphics or patterns instead of conventional dots to achieve the purpose of reproducing image tones and layers. The commonly used dot shapes of common screen technology are generally circular, elliptical, diamond or square, and the shape of the dot is controlled by the dot function. According to the Postscript screening principle, adjusting the mathematical model of the dot function can flexibly control the shape of the dot. This is the mathematical theory basis of the art screening technology.

Art screening is to describe the outline of the figure or pattern as a dot by certain algorithm, and then use the enlargement, reduction, or other non-linear transformation algorithm for the contour to make the contour curve correspond to the gray value of the image, and finally describe with the outline. The graphics or patterns complete the screening of the image. In the high-profile part of the image, the edge of the dot outline appears as a fish shape; the dark part uses a reversed dot, and the outline of the blank part shows an geese shape; and the middle tone part uses a fish shape and an geese shape to represent the ink portion and the blank portion respectively. Changing the mathematical model of the shape of the control network can change the shape of the fish and the goose into other shapes, such as various line patterns, to enrich the types of art screening.

Art screening technology is most suitable for large-scale outdoor posters and advertising paintings. What people see from a distance is the overall image effect of the screen. From the near place, they can also learn the special information contained in the outlets. In addition, anti-counterfeit printing is also suitable for artistic screening, and the microtext or icons (trademarks) are printed in the image as dot shapes. Since the dot contour algorithm is unique, it can play a certain anti-counterfeiting effect. If the anti-counterfeiting image printed after using microtext instead of halftone dots, the small text hidden in the image can be clearly seen with the aid of a magnifying glass, thereby playing a role in authenticating the authenticity.

Three-dimensional screening technology

As we all know, printed images are represented by two-dimensional structures. The three-dimensional screening technology is aimed at printed images. By precisely controlling the generation of dots, the effect of reproducing three-dimensional images in printed images can be achieved.

The basis of three-dimensional screening technology is still the orderly jitter and error diffusion technology commonly used in computer network technology. In the specific implementation process, non-traditional algorithms are used. After determining the dot shape, screen angle, and screen number, the computer automatically matches the screening template stored in the buffer, finds the closest template to the input, and then generates the dot. The shape of the dot is controlled by a dither matrix. The dither matrix may originate from a template that was previously stored in the buffer, or may be generated by the computer temporarily. The realization of the screening angle and the number of screen lines is completely controlled by the template matching function. The overall algorithm uses a combination of geometric transformation, template matching and effect dyeing, so that the screen image can be rendered as a three-dimensional effect as much as possible to improve the visual appearance of the image.

Normal screening and 3D screening are compared. The halftoning images generated by ordinary screening techniques have a clear tone and hierarchy, but lack three-dimensionality. The three-dimensional screening images generated by using three-dimensional screening technology not only have distinct levels and levels, but also have obvious stereoscopic effects. , More vivid, realistic, more in line with people's visual physiological habits.

Imitation physical screening technology

Imitation physical screening is the use of special network points instead of ordinary network to screen the image. The biggest difference between it and Art Screening is that the network points it uses are closely related to the overall image to be represented. Therefore, the mesh shape generation algorithm of the simulated object screening has an adaptive feature and can flexibly select the mesh point according to the content of the screening image. For example, when the printed image is a wall, a brick-like mesh point can be selected, as shown in FIG. 5a; when the printed image is an arc, a curved mesh dot can be selected. Therefore, the simulation of real-world screening algorithms is more complicated than the art screening algorithm.

Imitation nets are used to replace nets with multiple graphics. According to the texture of the screen images, a net point similar to the texture stripe is selected for screening. The process of imitation screening includes three steps, as shown in FIG. 6 . The first step is to generate the contour line according to the image texture, ie the stroke, the density within the contour line is uniform; the second step is to dye, that is to calculate the luminance distribution of the stroke area according to the pixel gray value, ie the density distribution; The third step is fusion, image fusion is performed on the contour line and the stained area, and an imitation object screening image is finally formed.

The network formed by imitation object screening technology helps people to understand the image information, and greatly reduces the visual failure caused by the dot shape, giving a realistic feeling and is particularly suitable for the screening of artistic prints.

In the above, several kinds of special screening technologies are introduced. In the future, with the development of computer technology and the improvement of computing speed, new type of screening algorithms will be continuously introduced. The types of special screening technologies will become more and more abundant and more practical. , And is expected to be widely used in ordinary print.

Source: China Design Printing Network