Improve the printing quality with CTP screening technology

The significance of eliminating the film in the plate making process is not only to shorten the process cycle, but also to remove the intermediate image transfer media, and to avoid printing plate misregistration and saving print preparation time. These on-machine improvements have brought direct benefits to printers. At present, CTP technology has been widely used, and customers have also raised higher requirements on printing quality. The high network cable that can be achieved by CTP technology can fully satisfy customers' requirements for printing quality.

The traditional AM point-of-spot technology adjusts the size of the halftone dottones through the screen, but it has limited capabilities in utilizing the advantages of the high cable. Although current CTP technology can convey detailed information that is difficult for many printers to use, most of the bright and dark-tuned image information is difficult to save only with AM screen dots.

Randomly distributed FM dot network technology is to control the dot size within the range that can be used by the printing press. However, there are also technical defects in the FM dot network, such as the appearance of particles in the flat screen. In addition, pure FM network technology is not easy to implement on the press, so it will prolong the process.

The composite network technology attempts to use the amplitude modulation network point algorithm to process the intermediate tone by compensating the inherent defects of the amplitude modulation network point and the frequency modulation network point, and uses the frequency modulation network point algorithm to handle the bright tone and the dark tone. However, this method will cause problems when converting from AM sites to FM sites. In most of the combined networks, the traces at the junctions of AM and FM sites are obvious, and the calculation of complex sites will prolong the prepress processing.

Therefore, it is a new challenge to develop a network technology that can capture the strengths of AM and FM network technology while eliminating the defects of the combined network technology.

CTP Technology:

The advantages of CTP technology: eliminating the need for film media and imaging the data directly on the printing plate; the increase in the accuracy of registration shortens the loading process by nearly half; the more precise control of the screen dot adjustment point enables high-quality printing. The convenience brought by CTP technology to production has prompted the printing companies to compete for new competitive advantages. In order to pursue higher printing quality, printing is performed using high-density lines with 175 line/inch and 200 line/inch dot lines. However, when using an AM screen point to print or control a 10 μm FM network dot at a high resolution, some alternative methods are still needed, which temporarily cannot satisfy the user's desire to easily obtain high-quality printing products.

AM network technology:

AM network technology is a kind of network switching point technology, which is widely used. The amplitude modulation process is to place a certain number of dots in a square grid with line/inch as the unit of measure. The size of the dot is adjusted according to the tone value of the picture, the dark tone zone forms a larger dot, and the bright tone zone forms a smaller dot. For two-color or four-color overprinting, the cable lines are arranged at a certain angle of the cable to prevent dot overlap and form rose spots. At high resolution, the AM dots can perfectly reproduce the midtones. However, in the bright and dark areas, the printer cannot control excessively small dots or blank dots, causing the dots to be lost, merged and pasted, making it difficult to reproduce images. Details.

Printing capability affects imaging quality:

The loss of outlets or the occurrence of stencils cannot be attributed to dot technology, which is also affected by the working environment of printing presses and printing shops. In most cases, the image quality of the computer-to-plate system exceeds the processing power of the printer, so the high-mesh lines that the plate can record are not easily transferred to the paper. If you have to keep small dots, the dark tone area will appear to be merged and paste, or small dots will be lost in order to keep the dark areas.

FM network technology:

FM networks, also known as random distribution networks, overcome many of the limitations of AM sites. The technique of adjusting the grid layout by the FM network technology uses the small micro-points ranging from 10 to 21 μm to adjust the density of the dots according to the image density or tonal value by adjusting the number or frequency of the dots without changing the dot size. Micro dots, though small, can be processed by plates and printers. Although these dots appear random or random, they are carefully calculated and carefully arranged to enhance the image's fidelity. With the clustering effect, the FM network achieves perfect reproduction of image details. The disappearance of the network cable no longer results in a halftone effect on the printed image. The problem with the FM network is that the distribution of the dots in the midtone region is not easy to control. Once the dots are connected or overlapped, variegated colors or spots will appear, which is especially noticeable in the flat screen.

When printing, FM and AM outlets will also face the problem of increasing the number of outlets. However, due to the different ways in which the outlets increase, it is difficult to adjust the color or tone. In addition, the abnormal FM moire formed by the FM network is clearly visible and repetitive, similar to the moiré and rose spots of the AM sites.

Combined network technology:

AM network technology and FM network technology have their own advantages and disadvantages. Combining network technology is trying to take advantage of its shortcomings and minimize its use, in order to make full use of the high quality and high production capacity of CTP technology, and provide a capability in prepress or printing. Effortlessly reproduce the original dot technology.

Combination scheme one

The scheme divides the image into several parts. At the details, random dots are adopted to capture the subtle differences in the hue. The flat net uses amplitude-modulated dots to achieve a flat mesh effect without noise. However, this solution takes longer to calculate, and therefore reduces productivity. In addition, traces at the junction of the AM and FM sites are clearly visible, making the reproduction unnatural.

Combination scheme two

The program uses AM sites to process midtones and uses FM sites to handle bright and dark tone. With this method, the amplitude modulation net points can achieve a soft reproduction effect, and with the application of a high resolution, fine parts can also be visualized. FM outlets can ensure that outlets are not too small, beyond the processing power of plates and printers. In order to avoid variability, the number of dots can be reduced, but the traces at the junction of the AM and FM dots are also clearly visible, making the reproduction unnatural.

Combination scheme three

The scheme distributes amplitude modulation network points through the frequency modulation method, and the detail reproduction effect is good and the frequency is moderate. However, the defects inherent in the FM network have not been overcome, and particles will still appear in the intermediate tone and the peace network.

Overclocking screening technology:

In order to obtain an automatically generated and realistic natural high-resolution network cable, it is necessary to integrate different technologies. The overclocking screening technology uses FM mesh points to capture details in the bright and dark tone areas, and uses amplitude-modulated mesh points to achieve a smooth gradient in the middle tone area. In addition, to achieve a smooth transition at the point of transition, we must also take into account the printing limit of the printing press.

In fact, the overclocking screening technology uses the FM outlets in the bright and dark tone areas, and uses the AM outlets in the middle tone to achieve a smooth transition at the outlets. Accurately calculating the image is no longer limited to switching between the AM and FM mesh points. For example, when reproducing a highlight zone, the AM dots will gradually become smaller to the minimum size that can be copied on the fly, and then fade out to replace the FM dots. In the same way, the dark tone area is also a smooth transition from one type of point to another, leaving no trace at the junction. The dots in the highlights and shadows may appear to be random, but not truly random. The FM network area uses a small dot network under the control of the FM mode. It is arranged in a certain angle line shape, which becomes the extension of the AM channel line to determine the angle of the AM cable. As a result, a brand new dot arrangement emerges, so it is named overclocking and screening.

Overclocking screening production capacity and printing performance

Overclocking screening technology can complete a 180-line/inch network cable reproduction with a resolution of 1270dpi. When the maximum dot-line number is 340 lines/inch, the required resolution is only 2400dpi. The printing press is a part of the image reproduction system. The overclocking screening technology is used as a guideline. In fact, what needs to be considered are platesetters, plates, chemicals, printing machines, blankets, inks, and paper. In the prepress process, it is necessary to create the tone curve required for each production network cable. The commonly used production line number is 210 lines/inch, 240 lines/inch, 280 lines/inch and 340 lines/inch.

The traditional AM outlets are better than FM outlets, and the printing process is more stable and more tolerant. Because overclocking screens are similar to AM screens, prepress operators can move, adjust, and preserve color as they would with traditional AM booths. However, with the increase of resolution, the stability of the modulation sites in the bright tone and dark tone areas will decrease, and the performance of the FM tone points will be reversed. Overclocking screening technology combines the advantages of both and extends the range of on-board stability.

When the number of lines is 340 lines/inch, the minimum screen point for over-screening is not less than 2% of the screen points with 175 lines/inch, so the detail and smooth transition can be easily reproduced during printing. No matter how fine and complex the image is, it can be easily completed, and it can avoid the appearance of typical defects such as moire when imaging AM sites. Even if the distribution of the dots is so fine, mixed color dots will not appear on the color image and the flat screen surface, and they will be created with C, M, Y, and K primary colors. The overclocking screening technology utilizes AM outlets to overcome the shortcomings of non-responsive color changes in the FM network, maintain gray balance, overcome the limitations of the ink sequence, and the effects of changes in speed and temperature.

Sublima first realizes overclocking screening technology

The company's invention patent Sublima realized the overclocking technology for the first time. Sublima developed and used two Agfa technologies—ABS balance network technology and CristalRaster.

Agfa's development of Sublima aims to optimize the system using existing printing conditions. Based on different market applications, Sublima sites are optimized to accommodate different press and paper characteristics, including both newsprint and flexographic printing, as well as commercial sheetfed and web printing. Once Sublima has determined the smallest and most easily replicated on-premises point for a variety of applications (eventually becoming the smallest dot that Sublima can generate), dots will no longer be smaller. For commercial use, Sublima can generate 210 lines/inch, 240 lines/inch, 280 lines/inch and 340 lines/inch.

Beta Sites from around the world conducted tests on Sublima and concluded that: 1) The network cable is not obvious; 2) The network cable is fine, and even thin fonts can be processed with four-color overprinting method. The printed results obtained are clear and sharp; 3 Solid and color reproduction is uniform, no roughness, color mixing without traces; 4 skin texture smooth texture, color accuracy; 5 zoom in or out without affecting the image details, the quality of the same; 6 the technology also expanded the availability of high resolution Paper types range from high-gloss coated papers to newsprint and translucent kraft paper.

Reprinted from: Printing Technology