From ColorWiki

Contents 1 The New G7+ Specification 2 G7+ 2.1 Some of the benefits G7+ provides: 3 In more depth: 3.1 Gray Balance 3.2 SCCA 3.3 High Density Smoothing 3.3.1 What to do? 3.4 New Targets 3.4.1 Verification: 3.4.2 Calibration: 3.5 Universal Characterization Dataset (UCD) 4 Curve+

The New G7+ Specification

There's an old adage that says there's an exception to every rule. That might be true, but when you end up with a lot of exceptions, it would seem that the rule might need updating.

In previous newsletter articles on G7, we have proudly bragged of adding new features that enabled our Curve software to be better suited for various printing technologies. For example, we added the "normalize high densities" function" - and a button for using "Native CMY."

While G7 works very well, these are hints that more can be done to improve calibrations in certain areas, and some of these improvements require the software to step outside of the specifications for G7 as it currently exists. Exception checkboxes are not ideal. The best way to solve this was to improve the G7 Specification.

G7+

G7+ was announced in January and introduced to the world at the Printing United Technical conference in Dallas in March (2024). Much new information is coming out about this new specification and we will try to update this article in its online location with any new updates as they happen.

As we say around here,"Once you have the transmission open on the bench top, you might as well go in and fix everything." Those who are putting this together are making good use of the "opening up" of this spec so that much can happen to make printing better- without making the lives of printers worse.

Some things you DON'T have to worry about

• If you're happily printing to G7 now, the addition of G7+ is designed to not upset the applecart. At typical commercial offset ink levels, G7+ should closely resemble G7 appearance.

• Images that were printed based on the GRACoL color space will work well in a G7+ workflow. And likewise, images based on a G7+ workflow will work fine in legacy GRACoL workflows without change.

Some of the benefits G7+ provides:

• G7+ datasets can be SCCA-adjusted by an unlimited amount without affecting G7+ compliance, while even a small SCCA change can damage a G7 dataset's gray balance.

• G7+ takes care of an issue where high-density printers would sometimes see banding in gradients (think deep blue sky images.)

• The new G7+ algorithm improves the gray balance even on strongly colored substrates.

In more depth:

Gray Balance

With G7, the gray balance process works best if the 300% CMY is exactly 0.0 a* b* (perfectly neutral). If your media and 300% CMY overprint are fairly neutral, this works fine. Many people don't notice what color "black" is anyway. But picture a strongly-colored substrate with low contrast: a yellowish newsprint. The color of the substrate will still show through all the gradients in the shadows toward black. A warm gray balance heading toward a neutral black will be jarring to the eye. The shadows would end up looking blue to the naked eye using G7 only.

G7+ adds a portion of the substrate color back into the calculation of the 300% aim point. The result is a natural-looking gradient all the way from warm highlights to warm shadows, for instance. G7+ will do the same color adjustment with any strongly-colored substrate - like fabrics, colored papers, and plastics. One way to think about it is that G7+ works like the Relative Colorimetric rendering intent.

SCCA

Packaging printers and commercial printers are commonly trying to print to GRACoL but often have to alter the GRACoL profile to reflect the paper white of the different media they are printing upon. This is a perfect opportunity to use SCCA (Substrate-Corrected Colorimetric Aims). In actual practice, when making even a small change to the substrate color, the G7-derived gray balance of GRACoL is messed up by SCCA. Gray balance produced by G7+ survives the SCCA process intact.

G7+ has been altered to use a similar algorithm to SCCA, so that color modified by SCCA will perfectly maintain the G7+ gray balance.

High Density Smoothing

This is the kind of feature that drives people in the marketing department nuts. High Density Smoothing (HDS) is the feature that does not show up in the user interface!

Curve4 has a checkbox so the user can enable the ability to "Normalize High Densities". The checkbox comes with a foreboding warning that using this feature could "cause shadow tonality to fall outside of the G7" specifications. At the same time, some people printing high density inkjet work found that applying the G7 solution to these dark shadow areas was wreaking havoc. The G7 algorithm recommends changes that do not make sense in some cases.

What to do?

Change the specification!

In layman's terms this new method makes use of the G7 method of CMY grayscale correction from paper white up to the 75% cyan ink level. Above that, CMY tonality is based on TVI curves taken from GRACoL 2013 (CRPC6). This Reference Print Condition has nice smooth curves going all the way up to full density, and it manages to tame the beast of high densities nicely. Naturally, there is advanced smoothing and other fancy math done to make the transition smooth.

It's also part of the reason why, if you're already printing to GRACoL 2013, that G7+ calibrations will not change things much at all.

With Curve+ there isn't a checkbox for "Normalize High Densities" because it's all done automatically. G7+ with HDS will allow smoother transitions in strongly colored gradients, and even flesh tones will have slightly improved contrast - a particular benefit to those in wide-gamut inkjet printing.

New Targets

Compared to a manual transmission, that automatic tranny on your bench involves more work to rebuild. In the same way, all this G7+ automatic goodness has added some new requirements, though they?re not too taxing.

In order to pass the G7+ spec more patch colors need to be measured than before.

Verification:

Before, to pass G7 grayscale, you needed to measure at a minimum, the G7 Verifier 54 patch target. With G7+ the minimal patches required are found in a new 84-patch G7+ Verifier target that adds the necessary CMY high density ramps.

Calibration:

When calibrating, there is also a new "P2P" target that is available for use. The P2P75+ target is like the P2P51 that most of us have been using. The difference is that it is optimized for G7+ by adding 75% and 85% patches of C, M and Y and removing the 95% R, G and B patches. The P2P75+ has the same number of patches as the P2P51 and takes up the same space on your press sheet, so it's another thing you don't have to worry about.

Note that with the Curve+ implementation of G7+, you will be able to continue to calibrate with the P2P51 target when needed. Curve+ will automatically interpolate the 75% C, M and Y patches using neighboring patches. And then of course when you are using the P2P75+ target, Curve+ will happily make use of those patches when it finds them.

Universal Characterization Dataset (UCD)

A final point to keep in mind is that G7+ is positioned to be easily adopted as an international standard. The industry expects this to be happening sometime in 2024. Whether or not your shop considers itself an "international printer", the more this specification gets adopted, the more it will be known, and the more people will be asking for it in the future.

Curve+

So far, this article has mainly been focused on the G7+ specification. CHROMiX has been an ardent supporter of G7 in our literature and products from the very beginning. In keeping up with industry advancements, CHROMiX has released Curve+.

Curve+ fully implements this new G7+ specification with the easy and intelligent software design you have come to know from our previous products. Curve+ is backward-compatible with Curve4 files, and will easily open Curve4 documents to allow saving them out using G7 or G7+ methods.

In a number of ways, you can think of Curve+ as being Curve5, but now we?ve settled on a name that doesn?t change which each major release!

To be clear, G7 is still fully supported in Curve+ and will be for the foreseeable future. The language in the original Printing United Alliance announcement suggested that G7+ was intended to replace G7 in the near future. In reality, G7 is expected to have a comfortable grand-fathering period (after all, there are tons of facilities and equipment G7 certifications that won?t expire for up to 2 years). We expect to support G7 in Curve+ throughout that period and probably a lot further into the future. We?re happy to support what people want to use. That said, we?re confident that the changes in G7+ are great improvements and in attention to keeping G7?s ?sweet spot? unaltered, will make the transition from G7 to G7+ smooth and very much worthwhile.

A great deal of effort has been put into making this adoption as minimally disruptive as possible. We'll have that transmission back in your car and have you on the road to printing success in no time! Be sure to contact us at CHROMiX or in our ColorForums.com with any questions that you have.

Thanks for reading,

Patrick Herold
CHROMiX