Has anyone been daring enough to attempt to apply the G7 Process and Gracol to a digital press? We are looking at G7 for our standard for process control in offset and switching to the Gracol standard and curious on how other digital / offset printers have approached managing to this G7 process and using Gracol color space as a standard for digital printing. Most digital presses come with a preset of SWOP, but few have Gracol profiles by default.

Since G7 is based on gray balance, how do you maintain the digital press any different? How are you finding the digital presses are in maintaining gray balance?

Hi Patrick,

We have been running G7 on our 74Karat offset press for a few months now. However, we are using more as a calibration, and we are running everything through a custom output profile. It's been working really good for us so far.

I don't see how G7 would apply to a digital press. Most digital presses have their own internal controls for density and linearization. As you state, most digital presses come with a SWOP preset, but this does not mean the press is actually calibrated to SWOP. It's just an input profile. If you are sending a job that is set up for GRACol, then you need to change the input profile to the GRACol one you are using. Piece o' cake.

I am very interested some form of process control for our new iGen, and if it works out, on our various other digital printers. G7 looks promising, with its emphasis on grey balance. Colour cast is one of our most frequent production colour issues, so controlling greys looks like a logical step in addressing this.

It would be simple enough to handle the input profiles, but wouldn't the DocuSP default calibration target file need to be replaced with a G7 target file? Then, a custom output profile, slightly adjusted to optimize grey balance, should bring the press within G7 specs. But will it stay there, or constantly drift out of spec?

SWOP appears to have adopted the G7 grey balancing method to some degree. What is the difference between G7 and SWOP? Is one more suitable to digital printing than the other? Is it even possible to set up such strict tolerances for a digital press? Most people in the digital print industry, at least here in Canada, have never heard of process controls so I've never found people to discuss this with.

We have experimented with Gracol and the G7 process with our Nexpress.

We achieve gray balance via our press matcher software from CGS.

I have used the Idealink software to measure the gray patches of test targets off the Nexpress and have it give me the curve data to then place in the Nexpress to bring gray back into line.

The trick is a consistent machine. The Nexpress stays very consistent for us to make this work. Rich black generation is the only area where we are greater then 4 Delta E from Gracol and we can maintain less then 3 Delta E to the 3 main gray balance targets.

Unless Xerox has improved the iGen3, I highly doubt it can maintain its consistency and color stability to be within spec. Also, if you are trying to do this, make sure you turn off the iGen3's default high GCR which will artifically and negatively impact the gray 3 color generation and give you the illusion you are matching gray but really its just black toner.

I've seen tests on the iGen3, Indigo and Nexpress, and the indigo does the best with achieving a pure gray balance but was unstable throughout the run. The iGen3 floated from a magenta cast to a cyan cast and the nexpress was visually consistent but not the best match.

Anyway, I hope that the G7 process is modified to include digital devices, but the reality is they are all different and require different processes to fix the inherited gray balance issues each RIP manufacturer has. The reality is it will be up to the RIP manufacturers to include some sort of gray balance monitoring beyond density control as part of the process control internal to the machine.

Thanks for the reply Patrick

Sounds like you are confirming my fears that the iGen is not stable enough to attempt a G7 process control. I was also thinking of using GCR to stabilize the greys, but I guess this is not such a good idea. Regardless of whether I can make G7 work, I'm still going to try to implement some sort of process controls. The Xerox guys have a press sheet indicating expected colour shift that looks encouraging. Maybe comparing these colours in EFI Color Verifier could establish a tolerance baseline of a sort. If it was within 5 deltaE I'd be fairly satisfied. They may no want to give me the sheet if they know what I plan on doing with it Xerox doen't like to talk about deltaE at all it seems.

ps Good work on the Today in Print podcasts, I've been going through them today.