The argument is that this provides consistency and predictability from design to press, and incidentally avoids some of the designers’ complaints of “why does this colour look so much duller in print than on my screen?”

The downside is that it obliges designers to understand colour profiles when they’d rather be polishing their creativity and their awards entries; less obviously it short-circuits some of the really high colour quality potential available from modern digital printing systems.

End-to-end CMYK working is fine and dandy for litho printing (or flexo) where there are international standards for ink colours, and any ink runs on any press. It gets more complicated with newer digital presses, because most current inkjets or electrophotography presses (ie dry or liquid toners) can exceed the colour range of standard CMYK litho.

The result is often referred to as ‘extended colour gamut’ (ECG), though the term also applies to techniques of using five or six process colours, even in litho or flexo, to exceed CMYK gamuts. But all these digital devices and ECG techniques are different from each other, with no standardisation or interchangeability, so you have to do a lot of profiling if you want them to be predictable and to match each other’s results.

As we explore elsewhere in this issue, (see Star Product, page 88)Konica Minolta has been selling very pure CMYK toners with very wide gamuts that it calls ‘high-chroma’ for years through five generations of its entry-mid level HC digital presses. These sell to users who want to offer eye-scorching colour for photobooks and the like, but don’t want to pay a fortune for the privilege.

Other digital printer manufacturers sell on the same idea. Fujifilm has long promoted the extended gamut available from its CMYK Jet Press B2 presses, while HP Indigo liquid toner presses sell well into high-volume photobook service providers because of their excellent quality in CMYK, even without the wider gamut but pricier option of HP’s IndiChrome six-colour process inkset.

Desktop and wide-format inkjets often have eight or more ink colours and are capable of colour quality that knocks spots off litho, though at much slower speeds, but they are often used for commercial cover work.

Even CMYK-only industrial wide-format printers for sign and display work often have impressive gamuts and may be able to extend them further by using extra channels to output orange, green or violet inks as extra process colours.

For a long time it seemed that digital press makers and users were mainly interested in downgrading their results to match litho inks made to ISO 12647/2 standard. The extra gamut was promoted as mainly useful for hitting Pantone colours that litho can’t manage without extra plates and inks.

This makes sense for brands running campaigns with lots of different print assets that may be printed on a variety of print processes in different print shops and even different countries. It’s not relevant where the jobs sell on the best possible colour, such as photo albums, posters, coffee table art books and the like.

Forcing all the workflows into a litho-targeted CMYK standard such as Fogra39 or 51 to match litho, means you’re wasting the quality potential of a wide gamut press and you’re not going to get the best possible colour from your device.

So today there’s an argument for keeping everything in the best colour possible, with the original gamut from the digital camera or scanner, and only processing it into separations at the latest possible stage, in the digital front-end/RIP which can take full advantage of the available gamut. This is loosely called an RGB workflow.

For instance John Davies, workflow product group manager at Fujifilm, says, “All of our systems that print in an extended gamut require images to be supplied in RGB, and our systems manage the extended gamut printing either in the RIP or DFE. Our Jet Press and Revoria POD systems do use slightly different approaches. Also, the pink toner in our POD presses is used as a fifth colour to extend the gamut.”

Paul Sherfield, a colour expert who runs The Missing Horse consultancy, says: “RGB working is nothing new. For photobooks and prints you can run as RGB and print with the maximum gamut. I’ve done quite a lot of work with customers on that and they can get staggering results. The latest APPE v7 front-end will handle RGB-CMYK and if the CMYK profile takes in the maximum gamut of the printer, that’s what you’ll get out from it.”

However, he warns “there are problems with PDF/X-4, especially outputting to a CMYK colour space. You don’t know what is happening in the RIPs – they may have different settings.”

The downside of digital presses is that unlike litho you can’t just slap on any specially mixed ink you want, to print spot colours. So digital presses tend to use their wider CMYK gamuts to print colours that would require add-on special fifth and six or seventh colours in litho. The great thing is that you can then get any number of ‘spots’ into the same job, rather than being limited by how many colour units you have, and you don’t need to wash up the colours between jobs. The issue is how to colour-manage the CMYK to be predictable (and match to litho if you really want to), while allowing the digital press to use its full gamut on the spot colours.

Note that more and more digital presses do have fifth and sixth colour units with interchangeable colours, but they are generally used for embellishment such as metallics or spot gloss, and there’s a strictly limited choice of special colours (some of which can be gamut-extenders). Only HP Indigo offers a wide choice of real spot colours, and its IndiChrome option is also the only six-colour ECG process set available on any digital press.

In a news story on Printweek.com last year (15 November 2024), Malcolm Mackenzie, director of colour and automation consultancy Colour Engine, said it was a “chicken and egg” situation if customers do not realise that RGB workflows are an option. “Big corporates have understood it, but they are probably still sending CMYK to the printer,” he said.

“A lot of people are now retouching in RGB, but they still have an antiquated system where they output the document to PDF and convert everything to CMYK. Working in RGB is not that big a shift for a lot of people,” he added.

The dominance of Adobe Creative Cloud from design though to PDF and then to print, has tended to hamper the understanding of RGB working options – Adobe assumes that ‘professional print’ always means CMYK (defaulting to the rather outdated Fogra39 for ‘Euro prepress’) or CMYK plus spots. It defaults to CMYK conversion when creating PDFs.

You can install more modern Fogra 59 profiles, which can take advantage of the wider CMYK gamuts of many current digital printers, but it’s not particularly intuitive. Likewise you can opt to maintain RGB based images and layouts in PDF generation, while preserving spot colours as separate channels which can be handled separately by a RIP. It’s not particularly well explained in Adobe CC, though PDF export options in the rival Serif Affinity suite make it easier.

With this in mind, Serendipity Software in Australia has introduced a new RGB + Spots Colour Support option for the latest version of its Blackmagic colour management system, Verify soft proofer and MegaRip renderer. This is a RIP-server solution originally developed for litho proofing on inkjets, that can also handle production on wide-format inkjet. Colour Engine is the UK agent.

Jason March at Serendipity Software told Printweek: “The PDF spot colours are almost always assigned a set of device values based on an assumed CMYK or RGB colour space. In most cases when printing from a desktop app, the spot colour values are simply rolled into the device colour’s RGB, or in the vast majority of cases CMYK, then printed.

“What Serendipity brings to the table is that for a known and defined spot colour that’s already in our database, we keep that spot colour separate from the rest of the RGB (or CMYK) process colour data, then merge it with the final print output after the rest of the PDF has been colour managed. What we have now added is that ability to separately colour manage spot channels, while simultaneously maintaining a fully RGB workflow from start to finish.”

Although Serendipity says this is unique to its software, Sherfield reckons that Adobe’s widely used APPE 7 digital front-end can do this too. “The Blackmagic stuff can all be done with Fiery RIPs. Fiery can be set to say Fogra 39 or 51 for CMYK, with the spots set to maximum gamut. So you could match your digital job to litho ISO 12647/2 and still get around 600,000 spots that hit 95% of the Pantone colours.”