Poster: Aiming for G7™ Master Compliance through a Color Managed Digital Printing Workflow
Dr. Haji Naik Dharavath, Central Connecticut State University; Hans Kellogg, Ball State University;
G7™ is a method which specifies calibration procedures for printing visually accurate colors with an emphasis on matching colorimetrically derived aim points for the print reproduction processes to print with a common visual appearance. Today, this method is used in many applications of printing such as offset lithography, flexography, and digital (color laser or inkjet). It uses a one-dimensional neutral print density curve (NPDC) to match neutral tonality/gray balance. Published reports reveal that there are two other ways by which G7 master compliance can be achieved: a) use of output device ICC profile, and b) the use of device link profile (DLP = source as GRACoL2013 ICC profile + the destination device ICC profile). This experiment used only one way (a) to achieve the compliance. G7 master compliance includes three compliance levels in the G7 master qualification: G7 Grayscale, G7 Targeted, and G7 Colorspace. These levels demonstrate G7 master capabilities of a print facility.
The experiment was conducted in a Color Managed Digital Printing Workflow (CMDPW). It was aimed at achieving the G7 master compliance through an ICC based color managed workflow (CMW). G7 calibration method, using the P2P251x target was NOT used to derive the device NPDC to compare with G7 NPDC for print (or press) runs 1, 2, 3, etc. The purpose of this project was to demonstrate the use of a complete CMW and meet the specified G7 master compliance levels in a CMDPW by creating and using output device ICC profiles. Test target TC1617x was used for the output device profile creation process. The digital color press used in this experiment is a Konica-Minolta C6000 bizHUB color printer (or digital press). It uses a Creo IC-307 raster image processor (RIP) server (front-end system).
Hammermill brand, 100 LBS matte-coated digital color printing paper 12” x 18” was used for printing the samples in the experiment. Prior to printing the TC1617x target for creating the device profile, the printer was calibrated according to its manufacturer specifications. The calibration data (range of CMYK densities) was saved in the calibration lookup tables of the RIP and a calibration curve was created. A total of 100 sheets/copies of TC1617x were printed with the calibration curve attached. Also, an amplitude modulated (AM) halftone screening with 190 lines per inch (LPI) was applied during the printing. No color management or color correction techniques were applied during the printing. Printed patches of TC1617x were measured in CIE L* a* b* space using the i1PROFILER application with an X-Rite spectrophotometer with an i1iO table and the data was run through this application. The printer profile was created and stored at the right location on the computer. The profile format version is 4.00. This profile was used as a destination profile (DP) in the workflow. The source profile (SP) used in the experiment is a GRACoL2013 for characterized reference printing conditions-6 (CRPC-6).
A custom test target of 12” x 18” was created for proofing and printing use for the experiment. The test target contained the following elements: TC1617x target, an ISO 300 and custom images for subjective evaluation of color and an ISO 12647-7 (2013) control strip. A total of 100 sheets/samples were printed by enabling the color management technique at the RIP. The digital press calibration curve, destination profile, and the source profiles all were applied during the printing. A total of 5 copies of TC1617x printed target images were measured in CIE L* a* b* space using an IDEAlliance (Chromix/Hutch Color) Curve 4.2.4 application interface with an X-Rite spectrophotometer with an i1iO table and the data was combined to run through this application. The combined data was analyzed by using the Verify Tool of the application to determine the pass/fail of G7 master compliance levels. Analyzed data from the experiment revealed that the printed colorimetric values (G7 Grayscale, G7 Targeted, and G7 Colorspace) are in match with the G7 master compliance levels (reference/target) colorimetric values (G7 Grayscale, G7 Targeted, and G7 Colorspace). Therefore, the press run was passed by the Curve 4 application.
The conclusions of this study are based upon an analysis of colorimetric data, visual assessment, and associated findings. The presentation will be limited to colorimetric and densitometric data only. The experiment analyzed the effect of output device profile on G7 master compliance levels. The guiding objectives of this study allowed testing of an accepted color management practice to gain a better understanding of the presumptions associated with the application of an output device profile. The experiment examined the importance of calibration and characterization process of the digital press which was capable of printing colors to match or be in proximity of G7 master compliance levels.
The findings suggest that integration of device profiles is important in a CMW and it also enables/allows the workflow process to meet the G7 compliance levels via ICC based CMW, instead of using G7 calibration methodology. This study represented specific printing or testing conditions. The images, printer, instrument, software, and paper that were utilized are important factors to consider when evaluating the results. The findings of the study cannot be generalized to other digital printing workflow. However, other graphic arts educators, industry professionals, and researchers may find this study meaningful and useful.