By Simon Eccles, Monday 21 August 2017
Over the past 25 years a whole alphabet soup of colour working ‘standards’ has been brewed up for the printing industry in the wake of the device-independent digital pre-press revolution.
Some of them are internationally recognised and implemented (ISOs), some are de facto but proprietary (such as Pantone), some are interconnected, others are confined to broad territories (mainly Europe, North America and Japan or the Far East). Some are different names for the same thing.
We get confused, we’re sure that newcomers to the industry get confused too, and only colour consultants and scientists probably have a complete handle on the lot of them. In an attempt to clear the fog, here’s PrintWeek’s jargon-busting guide to some of the key colour standards that you’re likely to encounter in day-to-day printing. It’s our first attempt; it may not be the last word...
This is the heart of most colour management systems, developed by the multi-vendor International Color Consortium since 1993.
The ICC profile system (ISO 15076-1) uses tiny files that let you transmit colour characteristic data from camera files and design software, to monitors, printer drivers, RIPs and controllers. It’s also used to predict the final printed appearance in on-screen or printed proofing systems.
This allows device-independent colour conversion – any input file with an ICC profile can go out to any monitor/output file with an ICC profile. You don’t need to know what the combinations will be in advance.
ICC profiles work through a standard colour reference space (called CIELAB). For instance a digital camera image in a page layout can be converted through the reference space and out, for example, to both a desktop Epson photo printer and a Heidelberg XL offset press, with their respective profiles ensuring that the appearance is broadly the same.
Generic profiles are often supplied by manufacturers with devices and software. However for greater accuracy you can create or modify profiles of your own individual devices, using a range of measurement instruments together with input targets or output patches and profile-generating software. X-Rite dominates the market, but other important instrument makers include Techkon and Barbieri.
Device Link Profiles
The reference space of ICC profiles can be a drawback if there are colours that must be preserved unchanged – say a Pantone brand colour or carefully tuned CMYK images with under colour removal (UCR) or grey component replacement (GCR). These may be lost when they go through the reference space and out the other side.
There are ways to get around this by telling the system to detect and ignore Pantone numbers in the file, or to preserve the original black settings.
The alternative is to use Device Link Profiles. These are pairs of profiles that convert directly from one colour set to another by using a unique look-up table (LUT) with no intermediates. Alwan Color Expertise, for instance, supplies LinkProfiler 5 software to set these up.
A commercial developer and seller of colour reference swatch books and associated support materials. Owned by measurement systems developer X-Rite since 2007. Pantone provides the most widely used references for specifying colours, which are de facto if not actual standards, used worldwide. Most corporate brand colours are specified as Pantone references.
The right to use the Pantone colour sets is licensed to other developers for use in design software as colour swatches, or in printer RIPs and drivers as conversion tables.
The core to the system are colour reference books, which contain small patches of ‘solid’ colours, with each produced by an individually mixed ink on a specially adapted press. Each colour has a unique reference number. There are 1,867 colours in the current Plus Series. There are also additional sets for metallic and pastel inks.
The core is the formula guide for coated and uncoated papers, that gives ink ‘recipes’ to allow every colour to be mixed as a spot colour from 14 base inks that are licensed by Pantone. This works fine for processes that allow spot colours, but process CMYK and extended gamut sets are more economical for many analogue presses, while the only digital process that supports specially mixed inks is HP with the Indigo liquid toner presses.
Pantone’s Colour Bridge guide shows all its colours with their nearest equivalent CMYK offset values on coated or non-coated papers. See also extended gamut for seven-colour printing.
This isn’t a standard, but a trend that affects some standards. CMYK process inks are strictly limited in their colour gamuts, with a lot of colours that they can’t match (oranges, russet browns, bright greens, pure blues, purples, etc). Many Pantone colours fall outside the gamut of standard offset CMYK, although many digital printers have wider gamut CMYK.
Extended gamut process sets are also available with six or seven colours (usually CMYK plus orange, green and violet, but sometimes including red or Reflex Blue). A lot of inkjet photo printers have some or all of these extra colours as standard.
The makers of the extended gamut ink sets will often describe the coverage of their sets as for example “85% of PMS,” or “90%” etc, where standard CMYK matches about 50 to 60%. This doesn’t say precisely which colours can or can’t be matched, but it’s a broadly useful indicator.
Usually the RIP or printer driver suppliers will look after the colour separations from RGB input files. Some printer companies have created their own swatch books of key Pantone values that customers can use as reference guides.
However, last year Pantone simplified matters with the introduction of the Extended Gamut Guide. This shows the results of seven-colour inks (in this case CMYK plus orange, green and violet) with 1,729 solid colours (it gives Pantone numbers and RGB values for the solid colours). It’s based on offset inks on coated papers, but can be used as an approximate guide to the capabilities of other processes with similar colour sets.
ISO print standards
The International Standards Organisation uses committees to create and maintain standards for a huge range of manufacturing and working practises across all sorts of sectors and industries.
ISO 12647 is the main standard concerned with consistent printing. It’s actually a set of related standards that are widely used by printers today to ensure that their processes are within internationally recognised tolerances.
The one most commonly used is 12647-2, which defines the results for CMYK offset printing (including heatset web offset). 12647-3 is for coldset newspaper web offset, 12647-4 is for gravure, 12647-5 is for screen process, 12647-6 is for flexographic packaging (flexible and card) and magazines; 12647-7 is for “Proofing processes working directly from digital data”, while 12647-8 is for “hard-copy validation print, directly from digital data”.
Most of these standards date back to the early 2000s, but some have been revised since, for instance 12647-2:2013, which uses the Fogra-51 (coated) and 52 (uncoated) CMYK characterisations and profiles.
Note that 12647-7 or -8 are not for commercial digital printing (-8 was originally devised to get around the colour limitations of CMYK digital toners in the late 2000s). There is still no proper digital standard, mainly because every manufacturer tends to have different gamuts in their own inks or toners.
Related to this is ISO/PAS 15339, a proposed new standard that defined how to get consistent colour regardless of process. This would have worked for digital printing far better than 12647, but was rejected at a late stage by the European and Japanese arms of the ISO TC130 committee that’s concerned with graphic arts standards. They felt it was essentially an ISO label slapped on the US GRACol G7 standard, which isn’t used much outside the USA. Its current status is Publicly Accessible Standard (PAS), which basically means you can work with it if you want to, but it’s not an official ISO standard.
A lot of original image files today start off in the Adobe Creative Cloud programs and are set up with its colour management. Unfortunately this is confusing, often outdated, and needs a book all to itself. It lets you choose ‘working space’ profiles and to assign output profiles. These are shown as a choice of RGB spaces (important for monitors but also for extended-gamut printing), and CMYK.
There’s a particularly lengthy confusing list of CMYK working space profiles, many of which are for US and Japanese printshops and a lot of which are obsolete. For UK CMYK purposes you’ll want Fogra-39, which corresponds to ISO 12647-2:2004. Even the very latest Adobe versions don’t provide the Fogra-51/52 needed for ISO 12647:2013. You can download and install these from the European Colour Initiative website at www.eci.org/en/downloads.
Although traditionally printers would ask for colours to be supplied as CMYK, extended gamut processes or photo quality inkjets need RGB input. This preserves the original gamut until the RIP/driver stage, where the colour separation is made according to the capabilities of the actual device.
In Adobe terms, if you intend to print with an extended gamut process, make sure your input files are RGB and choose one of the RGB output profiles if you don’t have a dedicated one for the actual printer. Adobe RGB (1998) tends to be recommended as best for print. ProPhoto has the widest gamut, but input files won’t necessarily work with this so may look worse than Adobe 1998.