PVG’s COET faculty highlights the importance of G7 press calibration
Dr Akshay V Joshi, professor of printing engineering department of PVG's COET & GKPWIM at Pune, co-authored a chapter in the book The Art of Creative Design and Printing, which he donated to the college's central library in September. The chapter serves as an effective guide for both students and industry professionals. Aditya Ghosalkar finds out how
15 Sep 2023 | By Aditya Ghosalkar
Aditya Ghosalkar (AG): What inspired you to write a chapter on G7 press calibration in a book?
Akshay Joshi (AJ): G7 press calibration is a globally recognised methodology for enhancing print quality and colour consistency. The objective to write a chapter is to provide education to the print community and create an awareness of the benefits, essential requirements, standards, and specifications needed for its effective implementation. In the book The Art of Creative Design and Printing, authored by Ebrahim Shahiwala, I have co-authored a chapter. This chapter is an effort to serve as a valuable resource and effective guide for both students and industry professionals in its practical application.
AG: How would educating students on this topic translate into practical implications within the industry?
AJ: A subject on process optimisation in printing is introduced in the BE (Printing Engineering) syllabus curriculum at PVG’s College of Engineering and Technology; GK Pate (Wani) Institute of Management, Pune. The inclusion of G7 press calibration in the syllabus curriculum shall improve their cognitive, affirmative, and psychomotor domains in learning. The students shall understand the standards and specifications required for G7 calibration. The practical application of G7 calibration shall develop their technical and analytical skills and improve their problem-solving ability. Theoretical and practical exposure to the students on handling colour measurement devices, software, and materials for G7 calibration methodology shall also open more career opportunities in pre-press, print management, and where colour accuracy and quality are of critical importance. Educating the students on the topics of press optimisation and calibration shall build a better-trained product for the industry.
AG: What is G7 press calibration?
AJ: G7 is a calibration and process control methodology developed by Idealliance that aims to achieve consistent and predictable colour reproduction for any printing devices. The ‘G’ stands for gray while the number ‘7’ represents four process colours CMYK and three overprints RGB which are monitored as per the ISO standards and G7 specifications during the calibration process.
It is a substrate-relative process that takes the colour of the substrate into consideration. The key elements in this calibration are tonality measured by density or LAB values and gray balance measured in CIELAB a* and b* values that give a common visual appearance across different devices.
AG: Why is its implementation a requisite for the print industry or converters?
AJ: Today, colour in packaging is the reflection of the brand and has an impact on customers’ choices. G7 calibration helps effective communication between the brand and supplier, improved turnaround times, and cost-saving goals for the printers/converters. Global brands extensively adhere to standards, which should now be firmly established in the Indian market. Indian brands should also adopt consistent colour quality, which in turn will boost brand recognition and facilitate easier product placement on store shelves.
It provides a better match between proof and print, and reproduces colours consistently irrespective of the substrate, ink, press, or environmental conditions. The productivity and efficiency of the printing machine will increase post-G7 implementation thereby increasing the profitability of the organisation.
AG: Any industry-specific standards or certifications (such as ISO, G7 Master) that need to be adhered to during the calibration process?
AJ: Yes. G7 press calibration adheres to specific standards based on ISO 12647-2 and ISO 13655 measurement conditions for varying characterised reference print conditions (CRPCs). The aim points and tolerances may vary based on the type of printing. The G7 Master Facility Qualification Certification is offered by Idealliance and awarded for various G7 compliance levels.
There are two specifications by Idealliance - GRACoL (General Requirements for Applications in Commercial Offset Lithography) and SWOP (Specifications for Web Offset Printing) for the certification. The G7 calibration is based on CGATS/Idealliance TR 015:2015 (TR015) which represents neutral print density and colour for K and CMY neutral scales. There can be custom-specific certifications for certain sectors in the printing and graphic arts industry.
AG: What are the compliances associated with G7 press calibration?
AJ: Depending on the type of printing and precision needed, there are different compliance levels - G7 Gray, G7 Targeted, and G7 Colorspace. G7 Grayscale aims at the most appropriate printing process while G7 Targeted and G7 Colorspace focus on matching the measurement data to the relevant specifications or CRPC.
AG: How do you correlate G7 press calibration and sustainability?
AJ: The implementation aims to achieve colour-consistent image reproduction by achieving global specifications. It reduces the need for conducting multiple runs, minimises ink and substrate waste, reduces set-up time, less energy consumption, and increases the efficiency of resources used such as ink, substrate, solvents, and other supplies. The effective management of resources and minimisation of waste shall reduce the emissions and carbon footprint of an organisation which is a positive step towards sustainability.
AG: Please elucidate on challenges faced in implementation?
AJ: The biggest challenge is the adaptibility and committment from the organisation to shift from the traditional printing method to a colour-managed workflow. It requires training, technical expertise, investment in measuring instruments and software, and a continuous monitoring system. However, the move towards the G7 calibration shall be a value-added investment resulting in significant waste reduction, and consistent print quality.
AG: Do you think the calibration can impact ink and substrate selection for printing jobs?
AJ: No. The G7 calibration process is irrespective of the ink and substrate used on the press. There is no G7 standard paper or ink, and the calibration can be done for any CMYK device on any paper and ink combination. As the paper manufacturers incorporate varying levels of Optical Brightening Agents (OBA) that yield variation in LAB values, so, the substrate white point is calculated using Substrate Corrected Colorimetric Aims (SCCA). Colour and gray balance are always relative to paper whiteness.
AG: Are there any known wear and tear issues with the press that need to be addressed during calibration?
AJ: G7 press calibration itself does not directly address wear and tear issues with the press. Routine maintenance of the press, good working conditions, and press stability are the key factors for achieving the tolerances and specifications for G7 calibration.
AG: Who is responsible for performing the G7 calibration, and what qualifications or training do they possess?
AJ: G7 experts and professionals who have undergone a training course program and qualified for the exam conducted by Idealliance are eligible to implement G7 calibration.
AG: How will the calibration results be documented and retained for future reference or audits?
AJ: The measured colour management data, and ICC profiles for CMYK before and after calibration for the given press, ink, substrate, and process parameters are documented in the G7 and pre-press software and retained as a reference for the production.
AG: What is the validity of G7 Master Qualification Calibration?
AJ: The G7 Master Facility Qualification Certification is valid for one year and should be renewed after 12 months.