How to measure digital printing with offset quality standards

The Bruner System Instrument Flight now makes it easier to assess the quality of printed products. The printed measurement and control strips were measured by a scanning spectrometer, the data was stored, and the best color correction values ​​were calculated based on more than 30 offset printing parameters. After comparing the printed products with the specified standards, the number of stars is obtained. The more stars, the better the quality (up to 5 stars).

In fact, this technology has been integrated on manroland sheetfed offset presses for quality control. This technology is combined with Quad Tech's on-line measurement and adjustment system, as well as web offset presses. Therefore, the time and material consumption on the printing press can be greatly reduced, and the ink color is kept stable during printing. In general, in order to control the final product quality of offset printing.

Proof Checker is an inspection software that was first installed and used in a printing plant in Switzerland in October 2006 as a supplement to Instrument Flight. The software is first used in the digital proofing phase. Using the Proof Checker software, the printer can determine if the print data provided is within the specified standard and whether it can be calibrated without any problems at the beginning of printing.

In addition, it does not matter whether the output device uses electrophotographic toner or inkjet printing, with or without dots. Therefore, the target group of Proof Checker software is not limited to offset printing plants, digital printing companies also use this software in order to improve its print quality.

1 Digital Printing

If we say that the comparison of different digital printing technologies has so far mostly been carried out visually, then for the first time the measurement technology of the "Brunel System European Standard" is used for comparison. According to the company, today's industry standards show the most accurate characteristics of standardized offset printing.

In this regard, Proof Checker software is mainly used for analysis and evaluation of digital printing systems. Apart from the software, the proofing zebra control bar is an important part of the inspection system for free downloading. Using this zebra bar, all the parameters of offset printing according to Bruner's European standard system can be collected, although the proofing is done with webless inkjet printing. of. The zebra strip is a measurement and control strip consisting of 5% to 100% of 20 steps, but the zebra strips are always alternated with the measurement color patches below 50% and the measurement patches 50% higher. Therefore, the contrast is generated sufficient to automatically identify small measurement patches.

The proof zebra strips were measured using a scanning spectrometer. The software analyzes and evaluates more than 50 parameters based on its effect on the color of the image, and uses 5 stars to evaluate the quality of the design similar to Instrument Flight. Uniform gray balance is the best quality.

Users of different proofing systems use Proof Checker software to verify that they can agree with offset standards under any circumstances. Whether it is an inkjet system or a toner printing system does not matter. Whether the color image of the printed image is formed by the amplitude modulation network, the line network, the frequency modulation network, or the color toner, these are indifferent to the measurement instrument. There is no need to worry about formulas and algorithms that are integrated in the software.

2 Inspection 7 Digital Printing Machines

In the series of trials, two A3 size Bruner system test versions were printed on Canon, HP Indigo, Konica Minolta, Kodak, Océ, Secco and Xerox digital presses. The test version consisted of different measurement components, proofing zebra strips and strictly required test images, which were subsequently evaluated by Proof Checker in a company in Locarno, Switzerland. The assessment results show that the digital printing systems of various manufacturers have basically reached the level close to the standard of offset printing in Europe, but all printing systems also have deficiencies. According to European standards, some printing systems still have obvious visual deviations from offset printing.

3 Uniformity of gray balance

This mainly involves a more or less jagged tonal value curve, which is too high or too low compared to the offset curve, or far apart. When the uniformity of the gray balance shows a defect, the level adjustment curve does not change. "Balanced uniformity" shows how unequivocal the gray balance reacts in the entire tone value range. The gray balance measurement section with 20 brightness steps is collected and analyzed in the new measurement component by the brightness curve and converted to a color measurement and displayed in the Bruner hexagonal system. 20 measurement points are used to display and evaluate the neutral gray axis deviation.

4 Inspection of the official print quality

In addition, changes in the process were analyzed from 100 consecutive prints per digital press and compared with offset printing. The results show that process variations are also related to machine conditioning and maintenance. Overall, offset printing now shows the best process stability.

Whether the effect of the digital printing system can be improved depends on its front and end systems and the possibility of intervention in ink and print control. Professional digital presses can perform this intervention in terms of tone curve, maximum density, and other adjustments, and can quickly reach higher quality levels.

5 Integrated Measurement

Now some digital printing system manufacturers have integrated measurement control technology into their printing system, which can automatically balance the measurement results on the rated value, or maintain the parameters in the digital printing system, such as temperature and air humidity stability. The use of Bruner systems and integrated calibration techniques can improve quality and achieve consistency with offset standards.

From the development of the Proof Checker software, it can be seen that web offset manufacturers using Quad Tech / Instrument Flight software have accepted the Bruner system's European offset standard. In addition, according to Bruner Systems, users in Germany stated that due to the large tolerances of offset printing process standards, they are in no position to respond to this standard. However, digital printers are interested in Proof-Checker technology.

Offset and prepress companies can not only calibrate their proofs against offset standards, but also calibrate their digital presses.

Digital printing plants can objectively test how their print results approach offset printing standards, optimize print output, and use it to attract customers.