‘Maintaining colour integrity across different substrates is a great question, but also one that can be relatively complex to answer in full. Different substrates can have very different white points, particularly in the world of digital printing and packaging. This white point effectively acts as the fifth colour in a typical four-colour printing process and can have significant and unavoidable impact on the end result,’ John states.
Indeed, when designers and brands make separations and proofs based on a standard profile like PSO Coated V3.icc, but the production run occurs on a kraft board, a colour shift between proof and production is inevitable due to the different substrate white points. This shift is most noticeable in side-by-side comparisons under a D50 compliant light source. As John notes: ‘Spectral measurement would clearly show this impact. Of course, when white points differ by a low Delta-e (dE), then impact is low and insignificant.’
Strategies for colour consistency
The key to maintaining colour integrity is acknowledging the unavoidable impact of a significant paper white shift. He explains: ‘It becomes important to create proofs and separations specifically for these paper types to realistically set the expectations of the designer and brands while giving the printer a realistic target.’
Today, many software solutions can use Substrate Corrected Colour Aims (SCCA) to create adapted ICC profiles for designers or aim values for printers based on different paper whites. According to John, when the production paper white point deviates more than 4 dE2000 from the proof or separation profiles’ paper white, then results become questionable, and a deviation of over 5 dE2000 indicates poor results.
Organisations like FOGRA and Idealliance have developed methodologies for assessing print across different substrates with varied white points. For example, G7 focuses on grey balance and tonality relative to the paper white point. John elaborates: ‘In essence, when grey balance is okay between two images we compare side by side, even if the colour gamut is not the same and the white points of the media differ, we say they have a common neutral appearance and are an acceptable match. The minute grey balance is disturbed on one image, perceptually we see an overall mismatch.’
Spot colour challenges
The discussion extends to spot colours in litho, flexo or gravure printing on different substrates. ‘When the ink kitchen formulating the spot colour ink is also given the substrate white of the intended printing substrate, the formulation will consider the effect of such substrate white and yield a very close match to the target colour. However, this, too, has its limitations,’ he explains.
For digital printing, unless a formulated spot colour can be run in a digital press, John believes the best possible match to that spot colour is achieved using CMYK or an extended gamut like CMYKOGV. ‘Provided appropriate profiles are used and the device profile contains a white point that matches your printing substrate white point, then using absolute rendering intent for your spot colour within the RIP is key to getting the best possible spot colour match relative to the substrate,’ he advises.
Navigating the complexities of colour management and control requires an understanding of the variables at play and leveraging the right tools and methodologies. By doing so, the industry can achieve consistent and high-quality colour reproduction across all media and substrates.
