The difference between true dot proofing and continuous digital proofing
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With the popularity of CTP technology, many companies have begun to use or prepare to invest in real-world digital proofing systems. In fact, the real dot proofing equipment has been appearing in independent form for several years. The most representative equipments, such as Fujifilm Finalproof and KodakApprovalXP proofing machine, can also be used for digital dot proofing.
If you use the 1-bit file explained by the output device RIP in the CTP process and select the corresponding software and high-resolution inkjet printer, you can achieve true dot proofing. The price of this proofing system is much lower than the previous one. And the proofing equipment, and the proofing cost is low, and the printing speed is also very fast.
This paper aims to analyze some differences between true dot proofing and continuous tone proofing, and to explore the issues that should be noted when purchasing a true dot proofing system.
First, what is a 1-bit file
1-bit files are RIP-interpreted data 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 three major manufacturers of digital inkjet digital proofing solutions available in the market: Best, which provides ScreenProof software, GMG, which has ColorProof software, and Serendipity, which supplies BlackMagic software. The first two products are mainly traditional digital proofing solutions, which expand the processing function of 1-bit files containing dot information, while BlackMagic software is a true 1-bit true dot proofing system that can use ICC. Feature file. Under market pressure, Agfa will also launch its own color spray point proofing system.
Second, the complexity of color management
In the evaluation of the proofs of the real network proofing, three factors are mainly considered, namely color management, reduction of outlets and subjective judgment. For a certain task, software and hardware have different combinations. At the same time, due to different tasks in practice, 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.
Continuously adjust the color management of the proofing. As long as the characteristic file of the printing equipment and the characteristic file of the proofing equipment are calculated, the proofs reflecting the actual effect of the printing can be obtained; in the proofing of the true dot, the color management is more complicated, on the one hand, because The -bit file is the data of the CTP RIP interpretation. It can be said that it has passed the "gate" of color management. The data (color) of the single color version has been determined; on the other hand, the RIP of the proofing system should not affect the generated as much as possible. Do not affect the accuracy of the proof output.
True network
In addition to the correct color, the real dot proofing should also be able to print out the dots that match the actual printing. Only when the settings are correct, can the dots and rose lines be judged, and the moiré can be observed. The inkjet printer's printhead is capable of ejecting very fine drops of ink, which is a prerequisite for accurate, complete dots, which requires the inkjet printer to have the highest possible resolution. The size and shape of the proofing dot must be the same as the printing time to ensure that the proofing effect matches the printing plate and printing characteristics (the dot gain rate). From the use of a magnifying glass to observe the printed proofs and the use of the true dot print proofs printed by the color inkjet printer, it can be seen that there are scattered, very fine ink droplets around some dots on the real dot proof proof sheets.
This is mainly because the principle of color inkjet printing is different from printing. In order to simulate printing color, it is necessary to rely on very tiny ink droplets to simulate the color information of the actual printing dot. The drop of ink droplets outside the dot area is a defect that cannot be completely overcome by current color inkjet printers.
2. Gray and dots
The continuous digital proofing system uses four-color analog gray. Since the current inkjet printer can produce very fine ink droplets, the color can be printed smoothly with the actual printed gray (such as 50% black) without affecting the gray vision. effect. In the real dot proofing software, there is a corresponding algorithm or an ICC profile (ICCDevice LinkProfile) connected to the device, so that CMYK can be directly converted into CMYK. In the real dot proofing system, the gray color is composed of black dots of different sizes. In order to match the gray in the printing, the dots will definitely change: or add color to each dot, but the color of the dot is definitely no longer Black; or the software adds very subtle colored outlines around a single dot. But there is such a question, what can these black dots have changed? Therefore, some people think that it is better 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 the color, the option of “absolute colorimetric” is no problem, because it can simulate the color of the paper. In principle, the proof of the real dot can also be selected. This option, but should pay attention to whether the quality of the dot is obviously affected, because the paper color can not be composed of the amplitude modulation dot, so the paper printing color and the amplitude modulation dot of the file will affect the dot observation effect; in addition, if it is in the real dot proofing The whiteness of the paper used is different from the paper in the printing. In order to reproduce the color of the actual paper as much as possible, the phenomenon that the aforementioned ink droplets fall outside the dot area becomes more serious, so the color spray is used to perform the true It is best to use paper with the same color as the printing paper when proofing, so you don't need to consider the color of the paper when using the ICC profile.
Third, the printer
Resolution
Since the resolution of the CTP plate making device is much higher than the resolution of the inkjet printer, the CTP device can obtain finer mesh points by performing true dot proofing, and even can perform FM dot proofing. However, for most CTP users, it is unrealistic to use CTP plate making equipment for real dot proofing. In addition to the cost factor, the use of CTP platemaking equipment for proofing must use special printing media, and the application range is greatly limited.
Most of the true dot proofing systems use large format inkjet printers. As for which type of printer is suitable, the main task types and requirements for proofing must be considered. Such as: simulate 150 line / inch dot, you can choose 1200dpi or 1440dpi inkjet printer, if it is a newspaper printing factory, you can choose a lower resolution printer.
2. Ink
Since inkjet printers sometimes perform proofing on officially printed paper, the use of pigment inks in inkjet printers is also a consideration. Because pigment ink is used to print on non-coated paper, the ink will not spread much on the surface of the paper, and the printing effect will be clearer and more delicate.
3. Multi-color printing
Inkjet printers should have more than four colors of ink. Using the printer's multicolor settings, you can accurately copy the spot colors. It is not important to have a light color in the ink because there is no corresponding color separation data in the 1-bit file.
4. Correction function
Whether the calibration function of the printer itself is complete or not determines the proof quality.
Whether the ink drops fall in the correct position may not be very important for continuous tone proofing, but it is a fatal problem for true dot proofing. Therefore, the printer should be frequently maintained and calibrated during daily use.
If you set the resolution of a large format inkjet printer to a lower level, you can use a plain paper to quickly print large-format "blueprint" large samples (that is, specifications to check the correct position and imposition of the layout). When users invest in large-format inkjet printers for standard-format printing, they should consider pre-reserving some functions for the printer in advance, so as to prepare for real-time proofing in future upgrades to avoid repeated investment.
Fourth, the test of the true dot proofing system
The quality of true dot proofing can be judged using Altona-testsuite (Visual) digital image files and ISO profile files. The test file can be visually measured and measured using the test instrument after output.
Fifth, RIP
The role of CTF/CTP RIP is to implement screening and color separation data, while the RIP of the proofing software recombines multiple color separation files into one file for inkjet proofing.
The CTP RIP must be able to completely store and output 1-bit files in the true dot proofing. Some CTP RIPs directly expose the output plates after interpreting the files. Such RIPs cannot meet the requirements of true dot proofing. If RIP supports 1-bit file storage, you should be aware of the file storage format and file name naming. When choosing a true dot proofing software, you should know the RIP type supported by the software.
After the 1-bit file data enters the proofing software, it should be processed in the following order: the file is correctly identified, interpreted, and the different color separation data are re-integrated together. This requires the proofing software to correctly recognize the 1-bit file. What color version corresponds to the data.
In the market, each manufacturer has different methods for naming files. For example, the naming of a single version has the following common methods: "name_c.tif", "name(c).tiff" or "Cyan-name.tif" "If there is a spot color, this situation will become more complicated." The variety of file naming may cause many problems in practice, and the digital proofing RIP must be able to identify the naming of all RIP output data in the market.
In most cases, 1-bit file output requires an extra expensive plug-in, but now with a proofing system that supports RIP output from a specific manufacturer, there is no need to export TIFF files, which is a very flexible solution. Users no longer need to purchase an output plugin. For example, if the user is using HarlequinRIP, BlackMagic software can be used without 1-bit file output. More and more vendors will adopt this solution in their software products. At present, most real-world proofing systems can only be purchased at vendors' authorized vendors. The significance of this vendor's sales strategy is that the personnel who sell the real-network proofing system need expertise and experience in many fields. System integrators should not only be familiar with the software operation itself, but should be familiar with the RIP and printing equipment of different output devices in order to flexibly combine different devices while demonstrating and solving their problems for customers.
Sixth, the conclusion
At present, there is no perfect true dot proofing system. If only the quality of the dot is judged, the quality of the true dot proofing using the CTP device is the best, but the type of the printing medium is limited, and the inkjet printer mentioned in this paper is used. True dot proofing systems can support multiple print media. When choosing a proofing software, consider the file format it supports. The printer should consider its resolution, print speed, and variety of print media. There may be some drawbacks to using an inkjet printer for true dot printing in a short period of time, but it is important that most systems now have the ability to print the actual moiré or trapping effect.