New G7 Pass/Fail Requirements
Along with the publishing of an updated G7 Master Pass/Fail Requirements (version 34, January 2018), IDEAlliance further revised the procedure and aim reference for all printers that are interested in becoming a qualified G7 Master Printer.
The article’s goal is to highlight the differences in the latest Pass/Fail Requirements versus the previous version 31 released in June, 2015.
Non-Standard Substrate (SCCA)
It is not uncommon for the actual press stock to vary from the standard substrates defined in the Reference Print Condition. When the difference is between a dE00 of 2 to 5, the CRPC data may be adapted using the SCCA (Substrate-Corrected Characterization Aims) method, which further creates a new sub-category of qualified conditions known as “G7 Targeted Relative” or “G7 Colorspace Relative”. Please note that a “Relative” production will look different from an “Absolute” reproduction but is still valid for qualification purposes.
Also, the latest Pass/Fail document clarifies that the target reference CIEL*a*b* values are subject to recalculation based on CGATS TR015 once SCCA is adapted. In other words, when SCCA is applied to the Reference Print Condition data, it only affects the colorimetric reference values of solid primaries(KCMY) and solid overprints (RGB), the rest is taken care of by TR015.
Sample submission Requirements
Within the past few years, IDEAlliance developed two new Test Targets: G7 Verifier and TC1617.
G7 Verifier is a new CMYK target designed for evaluating G7 Grayscale and G7 Targeted compliance levels. Since it contains the minimum patches required for G7 evaluation, it does not replace P2P25 or P2P51 as a calibration target.
And the TC1617 is a revised Test Target that eliminates the redundant patches in IT8.7/4 and replaces it with G7 related gray balance patches. For G7 Colorspace submission, if using TC1617, there is no need to submit a separate P2P chart.
G7 Grayscale Pass/Fail Requirement
“G7 Grayscale Compliance” is achieved when a device or process is calibrated to the basic G7 definition of constant neutral Grayscale appearance but does not use standard colorants or match a standard CRPC. It does not provide assurance of accuracy in colored image areas.
- The latest version of G7 Pass/Fail document has the same tolerance for NPDC (CMY and K-only scales) and Gray Balance (CMY scale only), while it suggests serious print providers should aim for half of the permitted tolerance values.
- G7 Grayscale now allows measurement in M0, M1 & M2 since G7 is substrate-relative.
- For print processes include flexo, screen printing, and electrophotography, certain exceptions provided by IDEAlliance are explained in Annex A, B and C.
G7 Targeted Pass/Fail Requirement
“G7 Targeted Compliance” is achieved when a printing process passes G7 Grayscale compliance and the CIEL*a*b* value on the primaries (CMYK), secondary (RGB) solid ink patches and substrates match a selected CRPC within
- Must meet G7 Grayscale requirements
- Must identify a G7 -based CRPC, either in public or custom domain (Custom Target)
- Solid and Overprints
The primaries (CMYK) and secondary (RGB) reference values can be either absolute value from the Reference Print Condition or revised version with SCCA applied.
G7 Colorspace Pass/Fail Requirement
“G7 Colorspace Compliance” is achieved when a device or process passes G7 Targeted Compliance and the CIEL*a*b* values in an IT8.7/4 (or TC1617) target match those in the selected CRPC within the following tolerances.
Please note, the 95th percentile dE00 for Proof tolerance has been tightened to a 3 instead of 5 from previous version. Also, the primaries (CMYK) and secondary (RGB) reference value can be either absolute value from the Reference Print Condition or revised version with SCCA applied.
Discussion
Due to the nature of shared-neutral gray balance, G7 is a useful calibration method regardless of print technologies and substrate. When you determine which Reference Print Condition (CRPC) is the best fit for your production, the substrate is one of the most critical factors that influences the final color outcome. Stay tuned for our next blog for how to use the latest GrayGuide feature on the TECHKON SpectroDens for various scenarios from proof to print.
