G7

http://www.idealliance.org/specifications/gracol/g7-vs-gracol

G7 is based on ISO 2846-1, which in turn is based on sheet-fed and heat-set web offset lithographic printing.

While it has certain applications for digital printing (proofing and cross-platform print being two examples), it also has a significant downside for digital print, in that you will likely sacrifice some color gamut in order to meet the G7 specifications.

 

For most digital printing applications, G7 calibrations still require icc profiles for achieve color matching. G7 calibration only addresses the neutrality of the CMY inks in combination. It does not address the neutrality of the black ink or the chroma of the CMY inks. ICC profiles are still required for this. However, G7 is a nice step for setting a baseline before profiling and ensures that your profile is doing as little work as possible. It is also a nice way to relinearize and validate your installed profiles. As mentioned above though, matching across multiple printers requires limiting the gamut of the print devices to the lowest common denominator.

 

Without any extra effort, the process of linearizing my inks (Mimaki ES3) brings them into neutrality. Unlike SWOP based offset inks, it would seem most digital inks don't require much playing around with different amounts of CMY to achieve neutrality.

Where SWOP inks need more C than MY and just a shade less Y than M to print neutral the digital inks seem to be designed to be neutral with equal parts CMY.

Is the G7 certification process designed to change the gray balance make up of the digital inks to mimic the SWOP based offset inks so you run the same "DeviceCMYK" PDF's without modification to achieve neutrality?

 

As I understand it, yes. G7 closely resembles swop when printed on a swop press and vice versa. G7 calibrations were designed to address the variances in neutrality from press to press. The SWOP specification as I understand it, basically consists of setting the density value for each ink color @ 100% and adjusting dot gain curves for each color. The theory is that when proper SWOP conditions are met, a SWOP separated image will exhibit good neutrality where needed. G7 on the other hand actually uses LAB measurements to exhibit neutrality from the shadows to the midtones to the highlights. SWOP requires neutral paper to exhibit neutrality whereas G7 is designed to appear neutral on both warm and bluish papers.

I should clarify that I am not a G7 expert or even G7 certified. I have read the white papers extensively successfully linearized a few grand format printers to G7 spec. I did this out of desperation because the company I worked for at the time had an early binding CMYK workflow, uncalibrated printers and no access to ICC profiling. Shadows were always blocked up, neutrals were never neutral and greyscales were always crossed over with banding. It was a nightmare and G7 happened to be the solution.

As far as neutrality with a regular linearization goes, I think some rips and/or some inks are better than others when it comes to this. It is irrelevant however once a profile is created and applied. At this point the profile handles the neutrality and the benefit of G7 seems lost except in the occasions where it is better to run with profiles off.