Application of universal proof digital proofing system and its color matching characteristics

Color management technology, digital proofing technology in the digital workflow needs, hardware and software developers, innovation, the promotion of the media, etc., in recent years in the domestic gradually recognized and adopted by the printing industry, using digital proofs as the same Zhang Also gradually accepted by more and more printing customers.

Color management and digital proofing technology are relatively new technologies and require users to have a deeper and more comprehensive understanding of color knowledge and printing technology. The author understands that some manufacturers who use digital proofing technology understand and assist some manufacturers in introducing digital proofing and related scientific research activities. They realize that the digital proofing system must be integrated with the factory's existing technology faster and better. The proper function requires system vendors to do more technical service work. It requires the printing plant staff to do more communication and digestion. The introduction of digital proofing system is not only the introduction of a device, more importantly the introduction of a set of technologies and processes, sales of digital proofing system to a certain extent, is to sell color management and digital proofing technology services, not just to sell a customer An inkjet printer or a digital proofing software. Some users did not use the digital proofing system well, and even lost confidence in digital proofing. The main reason was the lack of sufficient technical support and color management knowledge, and insufficient understanding of the relationship between the color matching characteristics of digital proofing and the upper and lower processes. Here are some of our experiences and opinions in the actual work, hoping to play a role in the reader's digital proofing.

Digital proofing proofs accurately match the color rendering effect is the most basic requirement for contract proofing. At present, the contract digital proofing system can be divided into three grades. There are high-grade halftone digital proofing systems based on the technology of sublimation of Kodak, Fujitsu, DuPont, Imation and others. These systems can be well matched with the printing color effect, and can emulate regular AM screen dots, and some can also be used for proofing on coated copperplate paper; however, these devices are expensive and the price of consumables is also relatively expensive. Printing sites with high prices and high quality requirements are rarely used in China.

3M's DigitalMatchpirnt and Kodak's Approral system are two of the earliest products offering halftone dot digital proofs. The use of "dithering" or "random continuous screen" method to simulate halftone dots, but because the actual printing process is not using this method, it is not recognized in the industry.

IMATIonRAINBOW

ImationRainbow is the first dye sublimation color desktop proofing device. The Rainbow series is available in 2730 and 2740 models. The newly launched Rainbow 2740 has a maximum print area of ​​460mm x 310mm and includes bleeding lines. Samples with metallic and white ink effects can also be printed. The proofer has an excellent RIP 4.0 color correction software system.

FUJIFIRSTPROOF

The FujiFirstProof, introduced in 1996, has a unique analog dot capability that uses a hexagonal dot structure. Fuji's equipment is different from other equipment using traditional inkjet and dye sublimation technologies, but the pigmented laminated metal film used in Fuji First Proof is identical to the ColorArt system and is identical to the principle of traditional laminated proofs. In this way, proofs that are very close to the print are obtained, and the color can be adjusted based on the customer's color look-up table. The device can be double-sided proofed on coated paper (including metal) weighing up to 500 g/m2 by driving on a Mac and using the HarlequingRip.

DUPonTDIGITALCROMALIN

The DuPont proofer is driven by Postscript Level 2 Rip, an inkjet printer with four-color print heads. The price of the machine is so high that it appears on DuPont's technical support. It is installed, commissioned and maintained by the company's engineers, and DuPont is responsible for providing paper, ink and color management. The digital Cromalin also uses the System Bruner control strip to help calibrate and manage the system. The device also has new features such as automatic paper feeding and a print size of 520mm x 690mm. Digital Cromalin has the ability to produce true spot colors, not analog spot colors. DuPont devices have excellent color calibration and dot gain control.

Medium quality grades such as: Sai Ying's Iris inkjet printing digital proofing equipment, there are several large-scale printing plants in China, but the equipment and supplies prices are still high for the domestic printing price.

IRISREALIST

The more mature equipment is the Iris Realist series of Scitexo, which dominates the proofing market. Its new printer is based on IrisRealist and uses GMGColorproof professional software for additional color information. The output size of Realist5O13 is 533mm × 355mm, and Realist5030 can reach 533mm × 762mm. Both machines can use Adobe CPSIRips based on a PC or Apple computer or Scitex's own Ripro server.

AGFADUOPROOF

AGFADuoproof is a hybrid printer that combines a thermal printing and a dye printing method using a Seiko engine. AgfaFototune color software is provided with the device, with 300dpi resolution, printable format A3 (including bleeding), on the basis of printing, with 28MB memory and PostseriptLevel2 as a standard to establish Risc.

Popular grades include HPDJ5000 series inkjet printers, EPSON7000, 9000, 10000 series inkjet printers and other equipment. The cost performance of this type of equipment is better than that of most domestic printers and prepress service centers. Such equipment has made rapid technological progress. In the past few years, it was felt that as contract proofing equipment, there were still some original defects and higher consumables prices; in the last two years, there has been quality improvement, the effect is close to that of mid-range equipment, and the price of consumables has been accepted. There are also more paper types available. Digital proofing systems composed of such devices generally use FM screening to simulate the color effects of most prints, but they cannot simulate conventionally printed amplitude modulation dots. Many users of digital proofing have proved that if they can accurately simulate the color effect, it is not important to use conventional amplitude modulation dots. The requirement for amplitude modulation dots is mainly a matter of habit.

Most of the domestic digital proofing systems for the contract are made up of the above-mentioned universal inkjet printers. Compared with medium-to-high-end devices, these devices have some inherent deficiencies in quality; therefore, they correctly understand the color matching of such digital proofing systems. The characteristics, and how to tune the color of such systems to match well with the printed colors to be simulated, is very important to effectively use such systems and avoid their deficiencies.

We have conducted analysis and practical production applications for several models of this type of equipment (HPDJ5000, EPSON7000, 9000). Most of the current digital proofing systems are based on ICC color management technology for color matching and conversion work, so adjust the digital proofer to an appropriate state and create an accurate ICC color profile (ICCProfile) is a digital proofing simulation The first step in printing color. “Adjusting the digital proofer to an appropriate state” contains a lot of content. Different digital proofers are still different in some aspects, but they mainly adjust the ink output of the digital proofing machine for a specific proofing paper, so that the digital proofing is sufficient. The range of color gamut to accommodate the printing color to match, at the same time, to make digital proofing can reproduce a rich level. This principle is not easy to implement and requires a thorough understanding of the relevant printing processes and ink characteristics. The amount of ink is too large, although the color gamut is large, but because of some levels of parallelism, the matching accuracy of digital proofing is reduced. Finding the right amount of ink may require repeating the color profile several times. After you finish the ICC color profile, you first need to see whether the color gamut range includes the common printing methods and the color gamut of the ink.

This digital proofing ink output control will be inaccurate for the matching of Japanese ink printing colors in the green area and the field yellow, and the ink amount of the yellow ink and the blue ink needs further adjustment. After the adjustment was completed, the digital proofer was used to simulate certain printing conditions to output the 928 color blocks specified on ITB.7/3, and the difference between the actual printed IT8.7/3 color target was observed. In order to further evaluate the accuracy of the adjusted digital proofs matching the printed colors, we prepared a color difference evaluation program. In the calculation of color difference, using the CMC formula, the CMC color difference formula is closer to the visual characteristics of the human eye than the Lab color difference formula, especially to the evaluation of the color difference near the neutral gray; and the correct reproduction of the neutral gray color is very good for printing and copying. important. It is recommended that the user select the CMC method when evaluating color differences with instruments such as X-Rite 528.530.

After a certain degree of effort, the average color difference of the 928 color blocks specified in IT 8.7/3 can be less than 2 under normal circumstances. (At best, we can achieve an average color difference of 1.45, a maximum color difference of 6.55, and a color difference of more than 4 colors. 17 blocks, less than 2% of the total. Conventional proofing is difficult to achieve. The average color difference between two proofs is less than 2, but this does not mean that our digital proofing is already very good, or that it is better than conventional proofing. In fact, although the average color difference of conventional proofing is larger, often the color blocks have basically the same color bias, such as full-page partial blue or full-page yellow, etc.; the printer can adjust the amount of ink or water to the corresponding color plate After the sample. Although digital proofing has 97% or more of color and printing are very close, but there are 3% of the color and printing have a clear deviation, this deviation is not the overall consistent bias; if the 3% of the color mixed in one The image occupies an average area. At this time, the human eye is not noticeable, such digital proofs are very good, and conventional proofing is difficult to achieve; but when this 3% of the color becomes the main color of the picture, or a large area of ​​the background color, such digital As proofs, there is a danger that proofs will be printed on the same sheet, and it may be difficult for the printing staff to recover the colors. From another point of view, due to the inconsistency in the color proofing between the color proofing and the printing color, in order to let the digital proofing color fall within the adjustable range of the printing press, the printing operator will have a good chance of success, and the accuracy of the digital proofing will be required. Higher than conventional proofing. We believe that how to solve this 3% color deviation problem will be a special concern for hardware and software developers and users of such devices. It is recommended that users use the digital proofing process to make the bottom of the 3% difficult to calibrate color. After the digital proofing software completes proofing, it is best to give an evaluation of the reliability of the proofing, and indicate whether the proofing contains information such as the range of certain high color.

In addition, some of these devices have black ink color cast, such as one of the reddish, which also makes it more difficult to reproduce the color near the neutral gray, especially the dark neutral tone of the neutral gray.

Although this type of digital proofing system still has many areas for improvement, it should be said that it has reached a level of usability. In fact, even some magazines with high printing quality requirements (full four-color sheetfed offset printing) are recognized. Such digital samples can be sampled. Of course, the premise is to adjust well and use it correctly.