Standardized Printing in Practice |
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Do Lab values contradict or complement gray balance? What you should know about industry standards and why they will win through.
Looking at the debate surrounding "standardized printing" (in accordance with the Process Standard for Offset Printing = PSO), it is easy to get the impression that standardization is something completely new and is entirely incompatible with tried-and-tested printing methods. This is not the case. What is true is that, for a long time, every print shop has set its own standard, whether a specific solid density or optimal print contrast. Dot gain is never left to chance either and, for decades, has been based on guidelines issued by fogra (the German Research Association for Printing and Reproduction Technology) or the bvdm (the German Association of Print and Media). The main objective of standardized production is to ensure a consistent quality standard that can be reproduced as rapidly as possible. In principle, when implementing standardization, it is advisable to focus on the most frequent applications at the company in question. Operational benefits must be prioritized. It is not always the highest-quality printed materials that require standardization, but rather the every-day products that need to be produced quickly with low margins. Exactly which standard is implemented is of secondary importance. What is important is that all parties agree on, and are familiar with, the standard that is to be used.
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Colorimetric values
A key new development resulting from the introduction of the PSO is the ability to specify solid colors and paper white using colorimetric Lab values. The main purpose behind this is to ensure that identical color values are achieved in different production processes. For example, the proof and offset print cannot be matched using a densitometer, but this can be achieved colorimetrically.
As a result, press operators will need to become familiar with the new Lab and ?E values. The spectrophotometer is replacing the densitometer. However, this does not mean that the familiar variables have to be abandoned. Cutting-edge instruments do not just show densities, tonal values, and ink trapping, they also use the ?E difference between target and actual values to automatically calculate the necessary press adjustments. Thus, the process of measurement and control is similar to the tried-and-tested method, except that colorimetry always adjusts to minimize the color difference.
Dot gain
Target values for dot gain are described for the 60 lines per centimeter screen in the PSO. If finer screens or FM screens are being printed, the required print results should be specified before production starts. In the majority of cases, the visual impression should be the same. Standardization authorities are currently working to specify a single dot gain value for all autotypical screens. This would create greater clarity and enable the industry to take another step forward in standardization.
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Gray balance
However, the question remains as to whether an even gray balance can be achieved directly in the individual colors despite correct solid colors and dot gain. Nevertheless, this should always be aimed for when calibrating the print process. In practical terms, for years this could only be achieved without CtP by changing the ink applied during printing. However, changing the amount of ink applied to the paper not only alters dot gain, but also affects the saturation of solids. It is better to adjust the printing characteristic at the prepress stage. This enables the printer to utilize the dot gain and solid color tolerance. It is then still possible to use the traditional method to even out day-to-day variations within the press tolerances. If a gray balance cannot be achieved within the tolerances, or varies to a large degree, changing the ink can help, especially if low coating thicknesses are printed with highly pigmented inks.
Spectrophotometry is ideal for checking gray balance. Using Lab values enables the operator to accurately determine whether the measured value is neutral and to what extent it deviates from a single color black. If gray tones are first defined colorimetrically using objective values, this can be used later as a basis for subsequent adjustments. It would then also be possible to match it to an enhanced black. The instruments needed for this already exist.
Optical brighteners
Using optical brighteners in printing paper creates false measurement results because measuring instruments interpret the UV light produced as a color, even though it appears white to human vision. This can produce significant irregularities in some cases, particularly when measuring tonal values. fogra, bvdm, and major manufacturers in the print media industry are currently working on a solution for this problem. Experiments using UV suppression filters to identify the UV component have so far produced promising results. Once testing has been completed and a practical solution developed, the ISO standard will be extended accordingly and adopted in the PSO.
Outlay
Standardization is not possible without additional outlay, learning, and communication between all parties. Standards such as ISO 12647-2 and the PSO provide a guideline and objectives. However, they do not cover every single process and possibility. It is therefore important that discussions still take place before the start of production to ensure that the desired results are achieved and that all parties are talking the same language. Nevertheless, without standards there would be no reliable way to manage colors or ensure true-color proofs.
Cost-effectiveness
This outlay does bring economic benefits, though. The certainty that the proof can actually be achieved on the press easily saves two or three pulls and provides reassurance during negotiations with customers. Colorimetric values are a valuable addition to quality assurance and analysis. In an integrated workflow, ink coverage values ensure that color presettings on the press are reliable, while Lab values provide the desired reference values for press measuring systems.
Conclusion
The trend towards standardization and specified values in the PSO make it possible to achieve previously unattainable levels of quality and color fidelity. However, everyone needs to be involved. A single proof for AM and FM screens will not work and using several color separation techniques on one print sheet has little to do with standardization. However, some people will have expectations that cannot yet be met, and perhaps never will be met. Standardization does not mean that the first pull will match the proof, even if the measured values in the quality control strip are already good. It may still be necessary to readjust the press. With the exception of inkjet printers, it is always easier to satisfy calls for narrower tolerances in the prepress stage rather than during printing. Paper is a natural product and ink is a complex chemical substance. Moreover, environmental and climatic factors influence both sheet travel and the viscosity of the ink. The press operator has to be fully aware of all these factors. Reliable standardized measured values and preset zone profiles provide welcome support.
And if the customer wishes to attend the coordination phase or wants the color correction omitted earlier to be lithographed on the press, that is all fine and proper, as the customer is always right. But then that has nothing to do with standards.
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Process Standards
Standards do not mean average or even below-average quality, they describe the exact coloring targets for printing.
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