P2QM--Prepress and Printing Quality Management

P2QM (Prepress & Press Quality Management) is a high-quality color management solution developed by Screen for digital workflow in response to the trend of smaller print, lower cost, and on-demand printing in the printing market. The centerpiece of the program is the production of color proofs and digital ideal proofs, while monitoring the changes that occur in color management in modern workflows.

First, the proof of the traditional workflow

In the color management process in traditional film-based workflows, color proofing can use chemical proofing or traditional offset proofing. In order for the printed matter to be consistent with the proofs, ink adjustments are required on the press. In the process, it is worth emphasizing the following three points:

1Special filming for chemical proofing is a costly production method.

2) Proofing with the traditional round offset offset proofing machine can indeed accurately simulate the effects of printed products, and often even exceed the quality of printed products.

3 Color adjustment on the press is a more flexible means of color control.

However, if we look at the above points 2 and 3 from another point of view, we can find that although offset printing can simulate the effect of printed products, it does not depend on the feeling and skill of the proofing operator. In addition, the intermediate stage of output film is time-consuming and material-consuming.

Second, digital proofing of CTP workflow

The CTP workflow eliminates the intermediate link of output film and widely replaces chemical proofing with DDCP (Color Digital Direct Proofing). However, there are some problems with the CTP workflow.

1  often does not support true halftone screen output, and the paper used for proofing is usually different from the paper used for printing. In this way, the matching of proofs and printed products is always subject to some restrictions.

2) Color proofs that can be accurately matched to printed products need to be digitally produced.

In the process of achieving the above-mentioned second point, the direction of the latest technology development is to use ICC preset documents to control the differences between equipment and various printing conditions, and to construct a system capable of simulating a printed product. The screen's "LabFit Color Management System" is precisely located here.

As we all know, CTP workflows make the best use of PDF data. In this way, the RIP-processed data can be used as the basic data for calculating the ink coverage, and the ink fountain key can be pre-set, thereby greatly improving the degree of automation of the preparation work before starting up. However, although the ink fountain key adjustment process is automated, it does not necessarily ensure that the printed product can accurately match the proof. In this case, the operator is still required to have a sufficiently high level to further finely adjust the amount of ink during the printing process.

Third, the CTP workflow proofing press

In the case where the DDCP system cannot completely solve the proofing problem, it is necessary to use a printer for proofing. In fact, this solution is feasible. This is thanks to CTP technology because it speeds up production. Of course, this also depends on the speed of the press.

In general, the proofs printed by the printer should be very close to the finished product. However, there are still some unavoidable obstacles that make the difference between the color of the proofs and the finished product, such as the uneven operator level and other subjective factors that exist during the press setup phase. In this way, the press operator still needs to make some fine adjustments during the printing process to match the printed product with the proof. Obviously, this will lead to a decrease in productivity. In the above situation, although only a few proofs are needed, it takes a lot of prints. In other words, all this leads to lower productivity and higher production costs.

Towards a fully digital workflow

After discussing the problems with the current color management solution, let us now look at how to really ensure the quality of the printing process. "To ensure print quality" - This is simple to say, but it is not easy to do because it means that there is a need for precise, digital control of the numerous adjustable variables on each press. Moreover, a printing company using a variety of brand presses is also a very common phenomenon. Therefore, any color management solution must be able to adapt to these complex environments. Although the CTF and CTP workflows avoid some of the dangerous situations that exist in traditional analog production methods, color proofing has become a difficult problem to solve. One of the biggest problems faced by current color proofing systems is that some of the colors they produce are the colors that printing inks can't represent at all. How do you talk about the digital control of these colors? As a result, you still need to rely on operators. The level of technology and feel.

The two most important factors we need to consider on the road leading to the all-digital workflow are: how to achieve the most effective color management; what is the best proofing method.

On the road to an all-digital workflow, the problems we need to solve are:

1. What is the best way to ensure print quality in the printing process after the CIP3-based ink fountain key has been set automatically?

2  How to realize the color management between different brand printers?

3 What is the best way to use ICC to pre-set documents?

In addition, as more and more printing companies begin to use digital printing presses, comprehensive and effective color management of digital printing presses has become an urgent issue to be solved.

The status of P2QM

P2QM is a comprehensive color management solution developed by Screen to provide full-scale workflow including pre-printing processes up to the printing process. It conforms to the international standards of the ICC and CIP3 printing industry.

Uniform color management of different brands of presses is feasible because the entire system of print production will be compatible with the widely accepted ICC and CIP3 standards. The main benefit of this is that the entire system will become more flexible and fully enjoy the benefits of digitalization.

At present, two main tools for improving the scientific precision of printing are the screen TrueFit and DCC systems. TrueFit is an on-line density measurement system that is currently installed on screens in the TruePress series of digital offset presses. DCC is used to provide print proof analysis data needed for automatic ink fountain key control. In addition, LabFit modules can be used to create high-quality ICC profiles to capture the characteristics of each press and ensure that the same quality is achieved in a variety of different output conditions. The P2QM elements TrueFit, DCC, and LabFit work together to implement the P2QM workflow.

The difference between the feedback loops in the color control process of the digital offset press and the traditional offset press is the individual TrueFit and DCC devices. However, since these two types of equipment control are basically ink density, the purpose of these two types of loops is actually the same. The purpose of LabFit is to work in the data stream that is fed back to the RIP. This is achieved by improving the RIP-processed data used in color proofing and printing processes and providing them with better RIP-processed data. The digital version of the ideal proofs is closer.

Therefore, there are two feedback loops in the P2QM workflow. Among them, the role of one cycle is to better calibrate the printer so that different printers can achieve the same print quality; the other cycle is to ensure that the proofing system is consistent with the output quality of the printer.

TrueFit

TrueFit is an on-line density measurement system that enables the screen's TruePress series of digital offset presses to maintain a consistently high level of quality.

TrueFit is installed in the take-up area of ​​the TruePress digital offset press and consists of a newly designed measuring head and light source unit. When the paper enters the delivery area, TrueFit can measure the strips on the printed sample in real time to more precisely control the density of the ink during the printing process.

DCC (Digital Color Console)

The DCC is equipped with a "full-shot once-shot" digital camera designed with a screen to faithfully measure color images. It can read color data on printed proofs, color proofs, and even standard proofs, and then analyzes these data to calculate CIP3 data and ink key data. There are three advantages to doing so. 1) According to CIP3 and color proofing data, the ink fountain key data can be calculated for the ideal printing proofs.

2) Even if no signal strip is used, the ink density data can be directly read from the graphic part on the printed sample sheet.

3) With the screen company's LabFit color management system, the LAB data can be calculated by reading the screen company's 85 color signal bars. In addition, LabFit can easily generate ICC profiles based on print proofs and proofs.

LabFit with 85 color signal strips

The 85 color signal bar used by LabFit is a newly developed technical result of Screen. It can generate ICC preset documents with a four-color printed narrow signal bar with only 85 color patches (usually, to generate ICC preset documents, a full-format color signal sample containing 800 to 1200 color patches is required. ).

The reduction in the number of color patches required to perform color measurements not only makes the color management process simpler and faster, but also allows us to easily arrange color signal strips on the layout during the normal production process. In this way, LAB data can be obtained from printed samples on a regular basis.

P2QM and Standard Production Presses

Another role of P2QM is to increase the consistency of the color of the offset printing machine. It accomplishes this through the following three approaches, each of which involves the screen's ICC:

1) Create an ICC profile for each major variable (printer, paper, ink, etc.) and DDCP system that affects print quality in LabFit so that color matching can be achieved from the perspective of these variables.

2) Obtain CIP3 data from customer-approved proofs, compare these data with digital proofs, and feedback the results to the ink supply system.

3) The color proofs and the proofs drawn during the actual printing process can be taken to the DCC for measurement and comparison, and the results of the comparison are fed back to the ink supply system.

The current use of the production printer's color management - output characteristics

The LAB data can be created by reading a sample sheet printed with a LabFit 85 color signal stripe at the DCC. LabFit can then create ICC profiles for various printing conditions. Similarly, LAB data can also be obtained by measuring proofs printed with DDCP printed with LabFit color bars. Subsequently, LabFit will create an ICC profile for this DDCP. Then, by feeding these ICC profiles back to the RIP, an exact match of DDCP prints and printed sample colors can be achieved.

Color Management for Standard Production Presses - Matching Digital Editions of Ideal Proofs

DCC is used to create CIP3 data for customer-approved proofs printed by current production presses.

By comparing this data with the data provided by RIP, it is possible to compare customer-approved proofs with digital proofs.

In this way, when building digital data, it is necessary to anticipate what kind of color correction is needed on the press. In this way, it is possible to implement operations based on ICC-preset documents including prepress operations.

Since the variable factors in the printing conditions can be controlled in a digital manner, it is possible to achieve a uniform print quality.

(Currently, not all vendors support this technology. To implement this type of operation, some systems will embed ICC profiles in image files. However, only some of the processes are currently running. Such as the realization of the CIP4 JDF After the format, it is expected that people can reach a consensus on this issue.)

Color Management for Standard Production Presses - Matching Color Proofing