One of the most overlooked—and most often misunderstood—elements in a colour-managed workflow is the input profile or working colour space. It provides a reference to the RGB and CMYK values in a document, which directly affects how much of an output device’s colour gamut can be addressed. One of the core concepts in colour management is the requirement for such a reference to allow the device-dependent RGB and CMYK colour spaces to communicate effectively with each other.
(Editor’s note: Again for the sake of illustration, a document that simply calls for ‘100 per cent cyan’ is roughly equivalent to asking a bartender for a full glass of beer. While the customer may get a glass filled to the brim, there is no guarantee of how large that glass will be or what kind of beer will fill it. A 237-ml (8-oz) glass of pilsner is very different from a 651-ml (22-oz) glass of stout, even though each can legitimately be defined as a full glass of beer!)
To get the desired output, it is important to provide a reference for the requested input colour values. This is where the input profile is a much-needed resource.
Colour standards such as the General Requirements for Applications in Commercial Offset Lithography (GRACoL) or Adobe RGB 1998 are common input colour spaces that define both the ‘volume’ and the ‘contents’ of the ‘glass.’ The GRACoL 2006 data set, for example, defines 100 per cent cyan with the L*a*b* values 55, -37 and -50, while the SWOP 2006 data set defines it as 57, -37 and -45; these are not the same colour. So, taking a document created with the SWOP colour space and then assigning GRACoL as the input profile would change the reference and create a colour shift before any inks ever hit any substrates.
While colour management is mostly a science, it also involves a dash of ‘philosophy.’ There are more than a few competing viewpoints about how best to handle files from outside sources, which can lead to frustration when attempting to rein in a colour workflow and determining which approach works best for
a given sign shop.
One effective mantra is “always embed, always honour.” This means when a file is saved, the profile that was used as the working colour space for that document should be embedded into it, if possible. Then, when that file is processed, the RIP software should look for the embedded profile and ‘honour’ it, rather than assigning a different one.
Indeed, reviewing the RIP software’s colour management settings is one of the best ways to take better control of colour management. Most RIPs provide the options (a) to use an embedded profile if one is available and (b) to assign a default profile if none is found.
While (b) is the trickier proposition, the safest bet is to select a colour profile that matches the default settings used by Adobe’s design software suite for CMYK and RGB colour spaces, i.e. U.S. Coated SWOP for CMYK files and either standard RGB (sRGB) or Adobe RBG 1998 for RGB files. Given these colour spaces are the most commonly used when new files are being created, chances are in the sign shop’s favour the designers have not changed them to anything else along the way.
That said, when incoming jobs place more emphasis on colour saturation than on image fidelity, an alternate colour workflow can then be considered. In these cases, it may make sense to ignore any embedded profiles and assign a larger-gamut input profile at the RIP stage. This approach will tend to use more of the output device’s extended gamut, but at some cost in terms of colour accuracy.
Josh Hope is senior manager of industrial printing business development and marketing for Mimaki, which manufactures digital wide-format inkjet printers and cutters. This article is based on a seminar he presented in October at the 2017 Specialty Graphic Imaging Association (SGIA) Expo in New Orleans, La. For more information, visit www.mimakiusa.com and www.sgia.org.