From FOGRA to G7 Master: Keyi Printing Earns Dual Printing Color-Process Certification

Keyi Printing, referred to here as Keyi, gained FOGRA color certification in 1998 with coaching from the Printing Research Center. The company then used the FOGRA standard workflow to generate TVI adjustment curves for Y, M, C and K. Even so, those curve adjustments did not fully solve color-reproduction accuracy—particularly for metallic product colors, where neutral-set overprinting makes accurate color difficult to achieve, and theoretical gray-balance dot values do not reliably deliver correct gray balance in print.

Because G7 color calibration addresses color control that includes three-color gray, Keyi added a G7 calibration initiative this year. In mid-May, with guidance from the Center, the company began G7 color certification and completed it in early July after repeated education, training and simulation exercises.

Following its full-process printing color certification from FOGRA, the German graphic technology research association (Fogra Forschungsgesellschaft Druck e.V.), Keyi Information Technology Co., Ltd. passed G7 Master certification under the Center's guidance. It became a company in Taiwan, China holding dual certification for printing color process.

Dot gain remains a central control target in print reproduction. A printer's prepress department must reduce plate dot output based on the press department's plate curve so the final printed dot values are correct. A typical example of TVI values against a dot-gain adjustment curve is shown below:

In that chart, the vertical axis is the dot size print reproduction aims to achieve, while the horizontal axis is the plate dot output after reduction to offset dot gain. The 45-degree diagonal in the middle represents the ideal printed dot value that plate dots can return to once printing dot gain occurs.

Both the SWOP standard and FOGRA control set out specifications to support stable, accurate print color. These controls are achieved by managing changes in single-color dot values for the Y, M, C and K inks.

During Keyi's certification, measurement-value discrepancies appeared. After comparison and analysis, the Center identified instrument consistency and measurement accuracy as critical. For G7 certification, hardware and software preparation matters greatly, especially the calibration accuracy of the measuring colorimeter, which strongly affects measured values. Thorough hardware and software preparation before certification can shorten the process and prevent unnecessary calibration rounds.

A system calibrated with G7 produces more accurate color after color management and keeps those benefits longer. G7 authorities recommend that printers repeat G7 calibration every two weeks or every month. In daily production, the main G7 control patches can be placed on the printing control strip to confirm normal system operation. Patches to check include:

Y, M, C and K solid patches (first-color printing)

R, G and B solid patches (second-color printing)

25% three-color gray (C25%, M19%, Y19%)

50% three-color gray (C50%, M40%, Y40%)

75% three-color gray (C75%, M66%, Y66%)

100% three-color gray (C100%, M100%, Y100%)

The Center's analysis and comparison of FOGRA and G7 color certification and control are summarized below:

G7 control method based on NPDC

Control highlight tone range HR (50C, 40M, 40Y), highlight tone contrast HC (25C, 19M, 19Y) and shadow tone contrast SC (75C, 66M, 66Y), while keeping gray balance at a=0±1.0 and b=-1±2.0

1. Printing preparation

CTP plate maker: verify that the plate dot output difference after linearization compensation stays within ±0.5%; select plate-making screen angles of K45°, C15°, M75° and Y90°.

Press: set fountain solution parameters at pH 4.8–5.5, liquid temperature 10–12°C and conductivity 800–1200 μS/cm; use the K, C, M, Y color sequence.

Paper and ink: use ISO 1# paper and ink that meets the ISO 2846-1 standard.

1. Printing screening standard: screen ruling 175 lpi; screen angles K45°, C15°, M75° and Y90°; round-square dot plate-making.
2. Density standard without the printing compensation curve loaded (note: color difference tolerances are L*±3, a*±2 and b*±2).

Once the standard is met, software is used to draw the NPDC curve (CMY three-color and K curves) and calculate the RIP curve for printing without the compensation curve applied.

1. Verification of the standard after applying the compensation curve: through NPDC calibration.
2. Creating an ICC Profile

TVI-based Fogra control method

Match the printed item's TVI curve to the original

1. Printing preparation: [CTP plate maker] verify that the plate dot output difference after linearization compensation stays within ±0.5%, with plate-making screen angles K45°, C15°, M75° and Y90°; [press] fountain solution parameters pH 4.8–5.5, liquid temperature 10–12°C and conductivity 800–1200 μS/cm; color sequence K, C, M, Y.

Paper and ink: paper meeting ISO 2846-2 and ink meeting ISO 2846-1.

1. Printing screening standard: screen ruling 175 lpi; screen angles K45°, C15°, M75° and Y90°; round-square dot plate-making
2. Density standard without the printing compensation curve loaded
3. Verification after applying the compensation curve: with the CTP dot-gain compensation curve loaded for printing, check that the 50% dot gain value remains within the allowable range
4. Creating and comparing ICC Profiles
5. Gamut comparison (on the same coated paper; the white line is the gamut from the G7 control method and the red line is the gamut from the Fogra control method)

● In shadow tones, the G7 method's gamut is much smaller than Fogra's but smoother, meaning G7 trades away color in shadow areas to prioritize gray-balance reproduction in mid and highlight tones

● In midtones, the G7 method's gamut is larger than Fogra's

● In highlight tones, the G7 method's gamut is roughly similar to Fogra's; only in red and yellow areas is the G7 gamut larger than Fogra's

● Overall, the G7 gamut is smoother than the Fogra gamut, with more natural tonal transitions, better matching the human eye's expectations for image reproduction. 2. Differences in operating methods

● Fogra TVI curve: the four colors can each reach an ideal state, but gray balance created by four-color overprinting cannot be controlled by TVI

● G7 control method

▓ Use the NPDC curve instead of Fogra's complex CMYK four-color TVI control

▓ Use HR instead of TVI values to reflect printed tone

▓ Use SC instead of print contrast to reflect gray balance in shadow tones

▓ Use HC to check gray balance in highlight tones

● The G7 NPDC method is simpler and also ensures that mid and highlight tones can be reproduced across different materials and equipment

After completing G7 color certification, Keyi took the strengths of FOGRA and G7 print color control and created a Keyi-specific color control guide together with the Keyi CPC ink control system. In the future, printed products from Keyi should see significantly better color accuracy and stability, strengthening customer confidence and quality performance. Keyi Information Technology Co., Ltd. has long followed the business philosophy of Quality, Service, Efficiency.

Beyond maintaining professional prepress and printing production technology, a high-quality service spirit and a rigorous work attitude, the company keeps introducing new technology and equipment. To ensure more complete, professionally stable quality, Keyi passed G7 Master certification in July under the guidance of the Printing Industry Research Center, a foundation, and received a certificate. It will continue applying print color quality control throughout production. This dedication to print quality demonstrates the strong capabilities of Taiwan, China's printing industry. In October, General Manager Shi of Keyi made a special visit to Chairman Chen of the Center and presented a plaque to thank the Center for its help with color certification.

—Reprinted from China Packaging Network (pack.cn); original link: http://news.pack.cn/show-361962.html