Next dimension?

The term 4D colour has recently come to prominence due to the publication of a white paper on acceptable working methods to achieve the ISO 12674 colour standard. A third working method of moving toward the ISO standard using 4D colour transforms has been proposed, in addition to the two accepted routes of tone value increase (TVI).

This has been largely followed in Europe using the Fogra methodology and neutral density approach, as advocated by US organisation Gracol and enshrined in its grey balance techniques.

When talking about 4D colour, you are really talking about ICC device link profiles. These are a subset of the ICC colour profiles familiar in colour management for describing and modifying the colour reproduction of digital cameras, monitors, proofers and presses. Those four dimensions don’t involve any scary science and getting to know the works of Einstein. They are simply the familiar process colours CMYK and each dimension refers to one of those separations.

According to colour consultant Paul Sherfield of the Missing Horse Consultancy, the clever thing about 4D is that it converts from one CMYK space to another, without converting to the Lab colourspace in the middle. This protects
the separations, including the black, and allows control of total area coverage (TAC) and grey component replacement (GCR). This is important, as it preserves and can enhance the printability of files. The benefit of this approach, when working in a colour-managed environment, is that it makes it possible to make adjustments ensuring you can hit the ISO 12674 standard on your equipment.

4D advantages
As for which method out of TVI, Neutral Density or 4D is the best, Sherfield argues: “There are marginal benefits to the 4D approach. It preserves secondary and tertiary colours better.” However, he cautions that these benefits, which rely on products that can carry out the 4D conversions, such as Alwan CMYK Optimizer and GMG ColorServer, can be washed away by the natural variance of the printing process itself. Despite his caution, he believes 4D offers the best means of adjusting separation settings when the output conditions differ from those the file was set up for, including optimising it for your particular press set ups.

Along with all the talk of printing to ISO 12647, there is also a move to supply files and proofs prepared to the Fogra 39L, which is what is known as characterisation data. Put simply, Fogra 39L is a description of the average colour reproduction of a series of print runs onto coated stock carried out under controlled and measured conditions to match the ISO 12647 standard. It fills in some of the gaps in the ISO standard to give a better description of what can be achieved on press.

However, working towards ISO 12647 also needs an ICC profile that takes into account different printing conditions, including the maximum ink coverage used in the separation –  a crucial control and one linked to the 4D colour issue.

For sheetfed work, the maximum ink coverage specified is 330%, whereas for web offset the maximum ink coverage, also referred to as TAC, is 300%. TAC specifies the highest allowable dot percentage of all four colours in a given area. If all four separations where set to a solid (100%), then the TAC would be 400%. A figure that high leads to printing and drying problems, so limits are set that produce the best compromise between the depth of colour and printability.

Web offset (also applicable for sheetfed long perfectors) has a lower maximum weight, due to the tougher challenges of printing at higher speed in one-pass, which physically limits how much ink can be put down before problems occur with the print process.

Impact of TAC
The TAC value has an affect on the appearance of the print, which means to go along with the Fogra 39L dataset are ICC colour profiles produced by the European Colour Initiative (ECI), ISO Coated v2 (ECI) and ISO Coated v2 300% (ECI), which are intended to be used throughout the workflow.

However, the differences between jobs produced to ISO 12647 with the Fogra 39L characterisation and those produced with different TAC settings are subtle, which makes it possible in many cases for the printer working to those specifications to optimise their separation settings for their presses and operating conditions, while preserving the appearance of the print. This is where 4D colour and device link profiles come into their own. Within any colour separation, there are some colours that will look the same when printed that can be built from different mixtures of CMYK. In particular, it is often possible for neutral and near neutral colours to replace mixtures of CMY with black to get the same colour, but using less ink, the GCR approach.

Colour management company Targetcolour is offering support to printers who want to take this approach of using 4D to optimise their colour.

“If you’re getting supplied CMYK files and you’re having problems on press, it’s all down to grey balance, which changes with every device,” says Targetcolour director Niall Coady. “We’ve used device link profiles comfortably for years in proofing to correct for grey balance, so why not for print – you have to rebuild the separations.”

Colour disparity
He cites an example of a client that was supplied a job with “decent files and proofs” that initially didn’t match on the sheetfed press it was being run on.  Analysing the dot gain settings in the RIP showed a different shaped curve was being used to the one recommended in the ISO 12647 standard, which was causing a disparity in the quarter tones.

“We re-characterised the press, put the information into Alwan CMYK Optimizer and when we re-ran the press it was an instantaneous match on press with the proof.”

Coady’s client is a lucky exception in getting decent files and proofs, according to Sherfield. He says that, despite the rise of ISO 12647, Fogra 39L and the ECI ICC profiles, too many clients still supply files separated with the wrong settings, often the defaults in Photoshop. There are moves afoot to get around that. Alwan, the firm behind CMYK Optimizer, has just tied up a deal with PDF pre-flight firm Enfocus to deliver a software package called PDF Standardizer, which combines Enfocus’ PitStop Pro pre-flight package with Alwan CMYK Optimizer and uses Enfocus’ workflow automation tool Switch to produce a single package that can pre-flight and correct files so they are PDF/X (ISO 15930) and ISO 12647 compliant. According to Alwan president Elie Khoury: “There really isn’t room for a margin of error in colour these days, people don’t have the margins.”

PDF Standardizer guides users through setting their files for the right printing conditions with a few simple questions. Even if they can’t answer those, it defaults to ISO 12647 and the Fogra 39L characterisation, which provides a basis for subsequent conversion if the printer needs to.

Sherfield says that the other approach printers are adopting is to devise a house colour standard and to provide clients with the correct settings for their own equipment and training on how to set themselves up. This is likely to become more common as printers move toward certificated accreditation to ISO 12647, which will require a colour management policy being put in place.

While dealing with additional dimensions of colour may at first seem scary, developments such as certificated accreditation and PDF Standardizer are adding dimensions to colour control that should, in the long run, make the process simpler and more reliable.

ACCREDITATION: ISO 12647

UK printers are set to become the first in the world to be able to be accredited to the ISO 12647 colour standard. The move, which was initiated last year by the BPIF Technical Standards Committee, is coming close to fruition with the first accreditations expected next spring.

To achieve certification, printers will have to prove they can print to the ISO 12647 standard and have a quality management system and procedures in place to maintain conformance to the standard, including proofing and a house colour management policy. The quality management system requirements will “borrow heavily from ISO 9001”, which should make it simple for firms with that standard in place to implement the colour standard too.

Print + Media Certification director Jon Stack, the accreditation scheme manager, is drafting the certification specification, which will shortly be submitted to UKAS for accreditation.

Print + Media Certification is in the process of training colour management specialists on assessing quality management systems and vice versa to ensure there is a pool of assessors to deliver certification.

The first printers are expected to be assessed in January 2009 and to achieve certification in the spring.

Although there are organisations offering certification already, none are accredited by a body such as UKAS, which guarantees that the certification is conducted competently, impartially and independently.