Analysis of Technical Advantages of Digital Proofing

Digital proofing technology is one of the hot technologies in the prepress industry in recent years. The so-called digital proofing is to print the page (or print) data produced by the color desktop system and output proofs directly through a color printer (inkjet, laser, or other means) without any form of simulation to check the image pages of the prepress process. Quality, providing reference proofs for the printing process, and providing the basis for users to sign and print.

This kind of digital proofing technology is not simply looking for printed color proofs, but through complex color management software, so that the output proofs can reproduce the matching proofs, including paper, ink and printability and other aspects of matching and similar.

For a long time, the effect of digital proofing is consistent with the simulated printing effect, and it is the main goal pursued by various digital proofing color management systems (CMS). Now the digital proofing system can not only output the sample structure of the FM dot and continuous tone, but also can output the sample of the AM dot structure exactly the same as the subsequent actual printing (line number, dot shape, dot angle and dot area). In this way, even if the color separation sheet has not been output or the printing plate has not yet been printed, the actual printing effect can be seen from the proof sheet, including whether there is a moiré pattern, whether there is a rose pattern, etc., and WYSIWYG is truly achieved.

Whether the digital proofing system can be applied in the pre-press field, and depends on the stability, consistency, output speed, and output of the system, besides whether the characteristics of the printing process such as color, gradation, definition, or dot gain rate can be reproduced. Size, system investment, cost of consumables and many other factors make people compare digital proofing and traditional proofing.

After several years of development, the output performance of the digital proofing system, the color management system for digital proofing, and RIP have all been significantly improved. Especially this year, after the digital proofing system breaks through the bottleneck of the output speed, this should be the beginning of the popularization of digital proofing technology in China's pre-press field.

Compared with traditional proofing technology, what are the features and advantages of digital proofing technology?

1. Color image reproduction performance

The color image reproduction performance includes the gradation range (also called contrast) of the image (including line text), the density or chromaticity of the solid or saturated color, gray balance, and the reducibility of the level curve (including the bright tone, intermediate tone, and dark tone levels. Reproduction and dot gain reproduction, fine texture, and more.

No matter what kind of color management software, by measuring the standard document color blocks to be printed and the standard document color blocks of the printer, the ICC format data can be obtained respectively. After the color management system software calculates, the characteristic calibration file required for the proofing process is established. Profile. In this way, all page image files that need to be proofed (including the data after the RIP of the PS and TIFF format files) can be output to match the subsequent printing as long as they are sent to the digital proofing system. No matter what type of paper is used for printing (such as coated paper, offset paper or newsprint, or even substrates such as plastics and paperboard) or what kind of ink series, the digital proofing system can simulate. If there are slight differences in the quality of proofing among various digital proofing systems, this mainly reflects the performance differences of the color management software they support.

Traditional proofing technology, because the proofer in the speed, pressure, imprinting methods and other aspects are different from the actual printing, so the traditional proofing is difficult to simulate the actual printing, printing is also difficult to catch up with the effect of the traditional proofing, and digital proofs in the actual proofs In use, the operator of the printing press generally feels that it is easier to simulate because the color difference between the digital proofing and the printing in the entire color space is smaller than the color difference between the conventional proofing and the printing.

2. Image Resolution

Since the digital proofing system usually uses inkjet printing or laser printing technology, the output usually is a frequency-modulated dot or continuous tone structure, so as long as there is an output resolution of 600 dpi or more, the proofs of the proof can achieve the effect of 150 lpi of the amplitude modulation dot. Most color printers today can achieve this image resolution.

The RIP of the next-generation digital proofing system can output amplitude-modulated dots that are consistent with the actual printing effect. Therefore, the printer is required to have higher resolution. At present, EPSON inkjet printers have an output resolution of up to 2880 dpi and HP inkjet printers up to 2400 dpi. The amplitude-adjusting dot images with the same output and actual resolution are no problem. Of course, from the actual network structure point of view, the dots on the proofs do not have clear printed dots. However, these fine differences cannot be seen with the mesh. What people need is that the visual resolution of the entire image can be the same as the print.

Traditional proofing may result in a decrease in image sharpness due to inaccurate overprinting, and there is no problem of overprinting in digital proofing.

3. Sample output stability, consistency

Undoubtedly, because the digital proofing system is sent directly from the digital page file to the proofing system, all the digital signals are controlled and transmitted before the proofs are output, so no matter when they are output, even if they are separated by weeks, months or even years, The output of the same electronic file is exactly the same. Of course, this stability is based on the premise that the performance of the color printer hardware, such as the size of ink droplets, ink, and printing, I can be consistent.

For traditional offset proofing techniques, paper, ink, and PS plates should be stable (actually difficult) and mechanical proofing equipment (such as platen "pressure", paper "pressure", blankets, and pads). The height, the pressure of the water roller and the ink roller, etc.) should be kept normal. The effect of the traditional proofing is also affected by the environmental conditions (temperature, humidity) and ink. The influence of many factors, such as quantity and uniformity, ink-water balance, etc., can not be consistent with the density of the connected samples in the proofing process, let alone depend on the operator's level and other factors.

Compared with traditional proofing, digital proofing is not affected by the environment, equipment, processes, etc., and is not affected by the operator. Its stability and consistency are very satisfactory. Therefore, the digital proofing system is used as a network proofing device. People can use digital proofing system to output proofs.

4. Output speed

For a long time, the output speed of the digital proofing system has always been the bottleneck for the promotion of the technology. Until last year, after a large-format, high-resolution inkjet printer appeared on the market, it took more than 40 minutes to output a large (102 cm x 78 cm) 720 dpi sample, which did not include the RIP interpretation time. At present, the output time of proofs with the same format and same resolution can be completed within 5 minutes. This type of proof output speed is much faster than the time for the traditional proofing (generally, the monochrome proofer completes four-color printing. The time for proofing the format takes about 2 hours). The reason why digital proofing speed is significantly accelerated depends mainly on the development of multi-nozzle inkjet proofing technology and rapid RIP proofing and server. Some proofing servers can control four digital proofers at the same time.

5. Proofing format

In the past, the general high-performance digital proofing system was mostly A3 (eight open) format. With the increasing resolution and speed of ink jet printer hardware, the increase of the capacity of ink cartridges, and the replacement of ink cartridges without stopping the use of ink jet printers, large-format ink jet printers have emerged in an endless stream. Currently, output widths of 1.5 meters or more have been achieved. Digital proofing system, various format models can simulate the effect of various printing presses.

6. System cost

The traditional proofing system not only requires expensive proofing equipment (more than 1 million yuan for imported monochromatic proofing machines and about 300,000 yuan for domestic proofing machines), but also requires matching proofing rooms (above 50 m2), air-conditioning equipment, etc. At the same time, it also needs to output the color separation film, printing support, proofing costs are considerable. The hardware of the digital proofing system is only the color printer, control computer, and supporting RIP and color management software. A large-format (large-split) digital proofing system, currently priced at no more than 120,000 yuan. Although consumables (such as ink and special printing paper) are still relatively expensive, the same amount of proofs and the same number of proofs (in four sheets) are still cheaper than conventional proofs. With the reduction of the ink cost and the promotion of imitating the special printing paper, the plain paper will be used for surface treatment and then output on the ink jet printer, so the cost of the digital proofing system may be reduced to a very low level.

At the same time, the space occupied by the digital proofing system is very small and there is no need for strict environmental conditions. Due to the absence of output separations, printing, mechanical proofing, etc., it not only greatly shortens the total cycle time for prepress design, production, and proofing, it saves a large amount of raw materials, and it also avoids the re-instatement of the proofs once they are found after the traditional proofing. Rework causes work and material waste. The digital proofing system can output proofs immediately after the original document is modified.

7. Personnel quality requirements

Traditional mechanical proofing (including the printing process) requires experienced and high-quality operators. When the workload is large, shifts need to be replaced. This will not only lead to instability in the quality of proofs (human factors), but also Increased production costs. The digital proofing system generally does not need someone, as long as the production designer knows how to use the proofing control computer. In addition, the digital proofing system can work 24 hours a day, all of which are unmatched by traditional proofing.

It can be said with certainty that digital proofing has become an irreversible trend to replace traditional proofing.

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