How to control the color of digital printing

How can we get good color reproduction on a digital press? “This is a fine balance issue,” according to Doug Polarkowshi, a technical expert at UARCO's printing department. “In order to explain the problem of toner on paper, I asked customers to recall a game that the older generation of children often play. Rub the balloon on the hair and then you can stick it to the wall. This game is easier to achieve than summer when the weather is dry, and toner is also the reason."

According to the point of view of the printing staff and the production center personnel, it is necessary to obtain good and stable color from the digital printing machine at the same time with the corresponding tools and experience. None of them believe that color control and calibration can achieve a fully automated process.

“We still need to have a good vision,” said Mr. Marc Orchant, the printing manager of Subia, a digital printing company. He said, "Also, when we deal with toner, we also need to consider the new color gamut." A Chrompress user, Mr. Orchant said, Subia company uses the company's most stable product - for example, like high resolution Films together with high-quality and same-sheet work in this area.

Next, the technicians created several test files that included hard-to-replicate colors and textures (like gemstones, skin tones, neutral grays, etc.).

Finally, after the devices were linearized, they calibrated the color scales under white light.

Now, manufacturers provide the company with many tools to help them solve this problem. Agfa now offers "second versions" of three types of Chromapress consumables (toner, developer and imaging drums), mentioned by Agfa's product manager. Agfa stressed that in order to avoid developer expiration issues, they already have a routine maintenance program.

Moreover, Chromapress devices can perform color registration and color density adjustments via the server and can be adjusted at random, and adjustments can occur on printed parts of all colors.

The thoroughness of this kind of work hopes to get results from IBM. Mr. Chris parker, commercial manager of IBM's color printers, mentioned that the company spent nearly a year before issuing their InfoColor 70 products and tested 10 identical Xeikon printers. "We try our best. The results show that the area of ​​greatest change has been found in the display effect between the device and the device, and the results clearly show that the problems posed by calibration, printing materials, or any other change factor are much smaller than those caused only by the actions of the operator. The software may just change in the registration problem, and many operators may produce several changes, resulting in a great deal of waste.” Mr. Parker believes that this trend is mainly from the offset printing experience of operators, “ For offset printing, just leave the device on until the color on the ladder looks good, but it is not appropriate for digital presses."

Interestingly, Mr. Parker claims that the problems with color and press control in digital printing are basically the same as in offset printing. "For example, for a former offset press, the adhesion of toner is no different from the ink balance in offset printing. The drum voltage - has a great influence on digital color reproduction, somewhat like the pressure of a squeegee. On the digital press LED exposures can be compared with plate exposures,” he suggested.

IBM's long-term workflow analysis prior to the use of InfoColor 70 enabled Agfa to include fully automatic density measurement technology in their products. This product also features a built-in heating head (for improved humidity and temperature control) and a Gretag. Density meter. The latter device is plugged into the server, and as long as needed, the color value of the coded job can be prompted.

Furthermore, InfoColor 70 also provides: SWOP used for automatic color matching and extended color look-up tables with European specifications.

Mr. George Willock, president of ColorStream, is very familiar with InfoColor, a digital market development company that has sold 650,000 copies of the program in 90 days.

Mr. Willock said ColorStream users need color management user solutions. Unlike standard color tools for loading InfoColor devices, the company (and users) uses Color Partnership's OptiCal product to achieve high quality remote proofing and soft proofing over ISDN or T1 lines.

If offset color control is a goal, Indigo users are also eager to mention that their presses (Eprint 1000+ and Omnius) do the same. “It can get the best color quality,” asserts Charlotte Krebs, Hollis Digital’s Indigo Division Manager. “It's worth mentioning that Indigo's technology is unique among digital presses. It uses liquid colorants. Electronic ink to get high gloss, similar to offset printing."

Hollis, a digital printing company with 25 employees. Mr. Krebs said that the biggest difficulty now lies in matching the color reproduction of early printing or reprinted printing. The company keeps a sample of all the jobs to help with visual matching. “Sometimes, our operators can even remember exactly how a job is printed,” Mr. Krebs commented.

However, more systematic is that Krebs's staff formed some operating procedures: calibration equipment every day, its own color control page, and careful density measurement techniques (ensure that the device will not be over compensated).

If the color problem still exists, by outputting 3-4 proofs, "We will make adjustments on the press." If that still doesn't work, Mr. Krebs said they will return to PhotoShop to adjust the document. In rare cases, it is a mechanical problem. At this time, it is better to leave it to the printer to solve it, he suggested.

With Xeikon-based device output, the developer may fail if it is not held properly, just as the plate is worn during the production of Indiog (the voltage will decay). The old E-Print 1000 user and Mr. Mike Chiricuzio, general manager of Sequel Inc., said that he is pleased to have a new upgrade in his front-end software, which can synchronize the life of the printing plate and automatically perform change calibration.

In addition, for Sequel's more than 700 customers, the Indigo system can store density settings for each job to ensure color stability.

For most proofs handled by digital presses, climate control is the key. Sequel (at a humidity of 2%) has installed a humidifier near the press and even used it with the air conditioning system in the factory.

In order to get better color, Mr. Chiricuzio expects the emergence of a newer version of the Indigo ink system - ElectroInk III. He hopes that this system will provide a gloss match with the paper used by Sequel.

In the final analysis, digital printers did not agree on the level of color reproduction they could achieve. On the one hand, Indigo users like Mr. Krebs like to show off their copy of 2point text to their customers under a magnifying glass and say, “This is not possible with toner-based printing technology.”

Source of information: OneTwoFree.Sp

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