The difference between true dot proofing and continuous tone digital proofing

With the popularity of CTP technology, many companies have begun to use or prepare to invest in real-site digital proofing systems in production. In fact, the true dot proofing equipment has appeared in independent forms for several years. The most representative equipments include FujifilmFinalproof and KodakApprovalXP proofing machines. In addition, the use of CTP platesetters can also be used for real proof digital proofing.

If the 1-bit file explained by the output device RIP is used in the CTP process, and the corresponding software and high-resolution inkjet printers are selected, true dot proofing can be achieved. The price of this proofing system is far lower than previously mentioned. And proofing equipment, and proofing low cost, printing speed is also very fast.

This article aims to analyze some differences between true dot proofing and continuous proofing, and discusses the issues that should be taken into consideration when purchasing real dot proofing systems.

What is a 1-bit file?

The 1-bit file is interpreted by RIP and used for CTF or CTP output and digital printing. The 1-bit file is a high-resolution image. Each point in the image corresponds to each exposure point of each color version at the time of output. This one-to-one correspondence is the basis for ensuring that the proofing effect is consistent with the printing result.

At present, there are mainly three vendors that provide color inkjet real-site digital proofing solutions on the market: Best, which provides ScreenProof software, GMG, which owns ColorProof software, and Serendipity, which supplies BlackMagic software. The first two products are mainly traditional digital proofing solutions, which expand the processing capabilities of 1-bit files containing network information, while BlackMagic software is a true 1-bit true dot proofing system that can use ICC. Property file. Under market pressure, Agfa will also launch its own inkjet spot proofing system.

Second, the complexity of color management

When judging proofs of real network proofing, three main factors are considered: color management, reduction of outlets, and subjective evaluation. For a certain task, software and hardware have different combinations. In practice, because of different tasks, the configuration of the proofing system is also optional. For example, the requirements for proofing in packaging and printing are very high, and the requirements for proofing in newspaper printing are relatively low. some.

The color management of continuous proofing is only required to calculate the characteristics of the printing equipment and the characteristics of the proofing equipment, and the proofs reflecting the actual printing effect can be obtained. In the proofing of the real outlets, the color management should be more complicated. The -bit file is the RTP-interpreted data of the CTP. It can be said that it has passed the "gate" of color management. The data (color) of a single color version has been determined; on the other hand, the RIP of the proofing system should not affect the generated Outlets, so as not to affect the accuracy of the proofing output.

1. Real network

In addition to the correct color, True Dots proofing should also be able to print out the dots that are in line with the actual printing. Only with the correct settings can the dots and rose lines be judged in order to observe the moire. The print head of the inkjet printer can eject very fine ink droplets, which is the premise of accurate and complete dot printing. This requires the inkjet printer to have the highest possible resolution. The size and shape of the proofing dot must be consistent with the time of printing in order to ensure that the proofing effect matches the printing plate and the printing characteristics (dot increase rate). From the use of a magnifier to observe the printed proofs and the true dot proofs printed using the inkjet printer, it can be seen that there are scattered, very subtle droplets of ink around some dots on the true dot proofs.

This is mainly due to the fact that the principle of inkjet printing is different from that of printing. In order to be able to simulate the printing color, very small droplets must be used to simulate the color information of actual printing dots. The drop of ink droplets outside the dot area is a defect that cannot be completely overcome by current inkjet printers.

2. Gray and dot

Continuous tone digital proofing system uses four-color analog gray, because the current ink jet printer can produce very fine ink droplets, with color can be successfully printed out of the actual printing of gray (such as 50% black), without affecting the visual gray effect. There is a corresponding algorithm or ICC profile file (ICCDevice) connected to the device in True Dots proofing software.

linkProfile), so that CMYK can be directly converted to CMYK. In the true dot proofing system, the gray color is composed of black dots of different sizes. In order to match with the gray in the printing, the dots must change: or add color to each dot, but the color of the dot is no longer Black; or software adds a very fine color outline around a single dot. However, there are doubts that these black outlets that have changed can explain what? Therefore, some people think that it is best not to use color management for the black version, but to use density matching.

3. Conversion method

Another important point in color management is the conversion method. Since the most important thing in the continuous proofing system is to accurately restore colors, choosing the “absolute colorimetry” option is no problem, because it can simulate the color of paper, and in principle, proofing can also be selected. This option, but should pay attention to the quality of the network is significantly affected, because the paper color can not be formed by the amplitude of network points, so the paper print color and the file's amplitude modulation network overlay will affect the effect of network observation; In addition, if the proof in the real network The whiteness of the paper used is different from that of the printed paper. In order to reproduce the actual paper color as much as possible, the aforementioned phenomenon that the ink droplets land outside the halftone dot area becomes more serious, and therefore the use of the color inkjet is performed. For dot proofing, it is best to use paper with a color that matches the color of the paper. This eliminates the need to consider paper colors when using ICC profiles.

Third, the printer

1. Resolution

Because the resolution of the CTP plate making equipment is much higher than the resolution of the ink jet printer, the true dot proofing by the CTP equipment can obtain finer points, and even the frequency spot proofing can be performed. However, for most CTP users, it is unrealistic to use CTP plate-making equipment for true dot proofing. In addition to cost factors, the use of CTP plate-making equipment for proofing must use dedicated print media, and the scope of application is greatly limited.

True Dot proofing systems mostly use large-format inkjet printers. As to which type of printer is suitable, the types and requirements of the major tasks for proofing must be considered. Such as: analog 150 lines / inch outlets, optional 1200dpi or 1440dpi inkjet printers, if the newspaper printing plant can use lower resolution printers.

2. Ink

Since inkjet printers sometimes perform proofing on officially printed paper, the question of whether ink jet printers use pigmented ink is also a concern. Because when using pigment ink to print on non-coated paper, the ink will not spread on the surface of the paper, and the printing effect will be more clear and delicate.

3. Multi-color printing

Inkjet printers should have more than four colors of ink. Using the printer's multi-color settings, you can accurately duplicate spot colors. It is not important that there is a light color in the ink because there is no corresponding light color separation data in the 1-bit file.

4. Correction function

Whether the correct function of the printer itself is complete or not determines the quality of proofing.

Whether the ink drop is in the correct position may not be very important for continuous proofing, but it is a fatal problem for true dot proofing. Therefore, the printer should be frequently maintained and corrected during daily use.

If the resolution of the large-format inkjet printer is set to be lower, using plain paper can quickly print large-format "blueprint" type samples (ie, specifications for checking the layout position and correctness of the layout). When users purchase large-format inkjet printers for specification printing, they should consider preserving some functions for the printer in advance so as to prepare for real-time dot proofing in the future so as to avoid duplication of investment.

Fourth, true dot proofing system testing

You can use Altona-testsuite (Visual) digital image files and ISO property files to evaluate the quality of true dot proofing. After the test file is exported, it can be visually measured and measured using a test instrument.

V. RIP

The role of the CTP/CTP RIP is to implement screening and generate color separation data, and the RIP of the proofing software is to reintegrate multiple color separation files into one file for inkjet proofing.

CTP RIP must be able to store and export 1-bit files completely in proofing in real networks. Some CTP RIPs directly expose the output plates after interpreting the files. This type of RIP cannot meet the requirement for true network proofing. If RIP supports 1-bit file storage, you must know the file storage format and file name naming. When choosing real-site proofing software, you should understand the RIP types supported by the software.

After the 1-bit file data enters the proofing software, it should be processed in the following order: the files are correctly identified, interpreted, and the different color separation data are reintegrated. This requires the proofing software to correctly identify the 1-bit file. Which color version corresponds to the data.

In the market, all manufacturers have different ways of naming files. For example, there are some common ways to name a single cyan, “name_c.tif”, “name(c).tiff” or “Cyan-name.tif”. "If spot colors exist, this situation will become more complicated. The diversity of file naming can create many problems in practice. Digital proofing RIP must be able to identify the naming of all RIP output data on the market.

In most cases, 1-bit file output requires an additional expensive plug-in, but now that you have a proofing system that supports a specific manufacturer's RIP output, you don't need to output a TIFF file. This is a very flexible solution. Users do not need to buy output plug-ins. For example, if the user is using Harlequin RIP, BlackMagic software may not require 1-bit file output. More and more manufacturers will adopt this solution in their software products. At present, most true dot proofing systems can only be purchased by vendors authorized by the manufacturers. The significance of this sales strategy for manufacturers is that the personnel who sell the dot proofing system need many areas of expertise and certain experience. System integrators should not only be familiar with the software operation itself, but also should be familiar with the RIP and printing devices of different output devices so that different devices can be flexibly combined and at the same time demonstrate and solve their problems for customers.

Sixth, concluding remarks

At present, there is no perfect true dot proofing system. If only the quality of the dot is evaluated, the quality of the proofing using the CTP device is the best, but the type of print media is limited, and the inkjet printer is used in this article. Real Dot Proofing System can support a variety of print media. When selecting the proofing software, consider the file format it supports, the printer will need to consider the resolution