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Expanded Gamut Printing

Contrary to the primary motivations of former systems such as Hexachrome, where high impact images were the aim, the revived interest in expanded gamut printing has been driven by the potential commercial benefits.

The ability to accurately simulate a wide range of special colours from a fixed printing process brings huge benefits to the printer.

In lithography, with the conventional 4 colour printing process plus spots, packaging printers spend an enormous amount of time washing up between jobs, particularly with short run work. To be able to significantly reduce, and virtually eliminate this, could mark the dawn of a new age in process printing.

The new flavour of expanded gamut printing is not based around a process defined in any standard. It is a custom system where users define their own inks.

CMYK with an orange, green and purple (RGB) generally provided the largest gamut, with the specific colouration of inks being a choice for the user.

Of course an expanded gamut printing process is achieved through the addition of just one further ink. But for the needs of the packaging industry to be met, it’s realistic to assume a 7 colour process is the way to go.

Even in the relative utopia of a 7 colour process, not all special colours will be achievable. This naturally concludes the ideal of an 8 unit press, with the 8th unit being for the out of gamut specials. With coating requirements, we begin to look at 9 or 10 unit presses in single pass mode.

The capital investment and commercial costs of such a printing process have to be considered, and balanced against the cost savings of greater productivity.

Does the colorimetric science work? The answer to this, Steve believes, is yes.

There are a number of expanded gamut printing solutions on offer, and Heidelberg’s Multi Color Toolkit, and ESKO’s Equinox, are both good examples.

But the success and suitability of expanded gamut printing is much more than a front end workflow that produces colour separation profiles and expanded gamut ready artwork.

Perhaps the biggest challenge is print process control. Expanded gamut printing and the accurate simulation of special colours from a process, requires above all, a stable, consistent and repeatable print process. A high level of print quality management is essential. Press settings, maintenance and metrics become hyper critical. Rollers settings, ink/water balance, ink distribution and regulation processes must all be optimised and managed.

Sophisticated calibration maintenance and print colour quality monitoring systems, such as Mellow Colours’ suite of PQM software, are a must.

Expanded Gamut Printing - Mellow Colour

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Screening is a further area worthy of discussion, which presents its own challenges in expanded gamut printing.

Although most of the systems on the market purport no more than 4 colours in any one area, and replace screen angles with those of their complimentary colour (purple with yellow for instance) this does not avoid moirés in all cases. Running 4 strong colours such as cyan, magenta, purple and black will moiré in conventional AM screening (regardless of swapping angles).

So an FM stochastic type of screening is a must for at least one colour (if not all). Pre-press systems therefore need to be capable of selective FM screening for specific colours.

The requirement of absolute stability in the print process must also be considered in the screening equation. Can stochastic screening be controlled to the levels required for successful expanded gamut printing?

Perhaps the final big question is commercial acceptance. What were previously solid colours, are now being produced from a process (screened, albeit possibly FM). Will the brand, the end user, accept this? What is the benefit to them?

Micro text and fine white out of solid text is a good example of why the discussion must extend beyond just accurate colour reproduction. Tiny pharmaceutical micro text out of a solid ink is one thing, screening it is another.

But there are enough examples of where printing specials from a process will work well. The potential savings to the printer are immense, and where some of these savings can be passed onto the end user, there is surely a market. Other printing technologies provide interesting potential in the area of expanded gamut printing, and it’s interesting to watch the innovations being born from these.

So only time will tell if expanded gamut printing proves to be a life changer of MP3 and iPod proportions, or a fad consigned to the history books along with the Sony Walkman, and of course Hexachrome.

Steve Fowler is a Print Colour Specialist for Mellow Colour, providing training, consultation and print quality management expertise to Mellow Colours users worldwide.

Formerly with Heidelberg, Steve has 28 years experience in the print industry, has vast experience in ISO 12647-2 implementation, and led the way in initial expanded gamut printing trials at Heidelberg.

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