Colour accuracy and consistency are becoming increasingly important. In the offset world, the move is towards print produced to the ISO 12647 colour standard.

The problem for anyone producing digital print is that there are no standards for digital colour - neither toner nor inkjet. The ISO 12647 specification is process-specific and, while the most common part of the standard, ISO 12647-2, refers to offset reproduction, there are other parts of the standard that relate to other production processes, including gravure and flexo. Digital production was never included within the specification, so there is no part of the standard designed to reflect the realities of digital print.

"There is no official requirement for day-to-day and job-by-job consistency," says Andreas Kraushaar head of pre-press at Fogra, the German research body that also offers colour management and technology certification. "There is no standard, and there is no research to base that standard on."

Fogra proposes to carry out a research project into the quality and consistency of digital print, which it hopes to get the go ahead for by the end of the year.

In the meantime, although there is no digital standard, the rise of digital print and its use alongside offset means it is becoming more and more important that the output matches and is consistent, especially as strides are made in the offset market with ISO 12647-2 to introduce greater consistency.

According to Bodoni Systems managing director Ian Reid, the target people are attempting to standardise on is ISO 12647-2 for paper types 1 or 2, which are coated gloss and matt and commonly represented by the Fogra 39L dataset.
Immediately, most digital presses hit a problem because, bar the HP Indigo, they can't use those coated stocks.

"The problem is down to paper colour and ink, but primarily where digital devices fall down is on the solid ink colours," says Reid. "If you print a solid on toner-based presses it looks out (compared to 12647-2)."

For offset production, there is an ISO standard for inks, ISO 2846, which specifies the colour for ink needed to print to ISO 12647, there's no equivalent in digital, the pigments in the toners and digital inks aren't necessarily a close match to those laid down by ISO 2846.

Stumbling block
With no standard for digital press colorants, achieving a match is hampered from the off.

HP Indigo is an exception, as its inks are a close match colorimetrically to the ISO 2846 specification. Printers using Indigo technology report that ISO conformance tools, such as Bodoni PressSign and Mellow Colour ISO litho, show the Indigo conforms pretty much out of the box, as long as you practice regular maintenance and calibration.

Today, proofs are mostly produced using inkjet, but due to the rise of toner for short-run production and its lower
cost per page, it is increasingly being seen as a technology for proofing.

"With digital, you can proof and do production on the same device," says HP Indigo product manager, strategic marketing, Lior Lewin.

Within the ISO 12647 standard, there is a specification for contract proofing, ISO 12647-7. As a proofing specification, the tolerances are much tighter than for production. As previously explained by Bodoni's Reid, that creates a problem for proofing on toner-based printers as their colours aren't a close enough match to litho inks.

To get around this, Fogra developed what it termed FograCert Validation Printing certification. There has been much wrangling about whether to incorporate this within ISO 12647-7 or to implement it as a separate part of the standard as ISO 12647-8. This is due to concerns about its broader tolerances and the potential for confusion in the proofing market.

Filling the void
Despite the potential to confuse the market, Validation Printing certification has been leapt on by digital press manufacturers in the absence of a standard for digital colour as a guide for printers looking to invest in digital technology.
"Since there is no standard for digital, the vendors are appropriating Validation Printing," says Kraushaar. "It's not dedicated for production machines - it's missing specification for consistency on the run and from job-to-job."

So, it's not a guarantee that what you print will hit the standard, but it is an indication that the system you buy (and it needs to be considered as a system - it's particular to the workflow and substrates as well as the press) is able to get quite close to the ISO specification.

While some experts question the relevance of the scheme, vendors have got behind it. "Printers don't have money to spend on equipment that can't hit the target," says Xerox Europe graphic art marketing manager Job Rombout. "So they need tools that show their equipment can hit the target. Products that have this certification meet that benchmark."
Canon European marketing manager Mark Lawn adds: "There is an increasing demand for quality and the issue is how you measure quality. Validation Printing is one of those tools."

Canon has got FograCert for its ImagePress C1+, 6000 and 7000 series production machines.

Xerox has 13 printer and front end configurations in the 40-70ppm space that have Validation Printing certification from Fogra and aims for all machines and workflows to be certified in due course. At the higher end, the iGen4, in combination with CGS Oris workflow, has the certification and Xerox marketing manager for iGen and DocuColor Kevin O'Donnell says: "Our aim is to get compliance across all machines and all workflows." Its latest machines, the 7002 and 8002, are currently awaiting certification as they use a new toner.

Validation Printing certification is fine as far as it goes, but it's only part of the solution.

"It's fine for showing what the kit is capable of doing, but there is still the issue of day-to-day operation," says O'Donnell. "It's just like an offset press, if you want consistency, you have to put the work in."

Data issues
Finding precise data from manufacturers about the stability of their machines is hard, although, according to research carried out at Xerox's Smart Centre, typically the colour consistency of a digital press varies by a delta E of two-to-three. In the worst case, there are instances where machines can show variation in some colours of 12-13 delta E. As delta E is a measure only of noticeable colour difference, it is clear a delta E of 13 represents a glaringly visible deviation.

"One of the biggest issues is good paper husbandry," says O'Donnell. "People say a job has changed from week to week and we find they've printed it on a stock with a different white point, or just on the same stock but with different humidity."
In digital, you need to find different ways of working to provide stable colour.

"With litho, you've got a colour bar on every sheet and in a 5,000 run you've got the time and the materials to take a couple of hundred sheets to get to colour," says Bodoni's Reid. "With digital, there's no time or budget to adjust colour."

"We're trying to automate it, hence the inline spectrophotometers on our latest machines," O'Donnell says. "With them we can measure and control consistency over time."

The digital vendors use Validation Printing Certification as a benchmark for their machines, but acknowledge it's shortcomings for production print. EFI sales development manager Kerry Moloney says: "Validation Print was designed for proofing, not for production, so the rules aren't quite right. That's where future standards will need to come in."

BEYOND ISO 12647
Last month, the TC 130 committee – the group of experts who cover print technology for the ISO - met in Beijing to discuss the future.

Fogra’s Andreas Kraushaar chairs working group three, the group within TC 130 that is looking at the area of developing a future print standard. 

As for plans for a digital production standard – nobody knows today, he says. My expectation is to start an all new print standard with a new number and, unlike ISO 12647, it won’t be a process standard. With digital printing techniques, it is impossible to differentiate by technical results. There are no longer clear sub groups by technology. Different parts of the standard won’t refer to different technology, but for usage cases with agreed criteria. Customers don’t care about the process, but about the result.

He believes that the key consideration will be achievable colour gamut, but other issues including resolution and light fastness will also be important.

It’s very early days at the moment, which means there is an opportunity for the industry to provide its feedback on what it considers to be important for the next standard.

There is no draft, there are ideas and concepts and the plan in Beijing was to get agreement to start work to create an all-new document, says Kraushaar. We’re calling for people’s thoughts and ideas.