Colour Matching

Labels printed digitally are produced using a CMYK colour model which is a subtractive colour model, and is also used to describe the printing process itself. CMYK refers to the four inks used in the printing press, namely: cyan, magenta, yellow, and key (black). Though it varies by print house, press operator, press manufacturer and press run, ink is typically applied in the order of the abbreviation.

The "K" in CMYK stands for key since in four-colour printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. The CMYK model works by partially or entirely masking colours on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" brightness from white.

In additive colour models such as RGB, white is the "additive" combination of all primary coloured lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural colour of the paper or other background, while black results from a full combination of coloured inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colours are produced by using black ink instead of the combination of cyan, magenta and yellow.

So in practice this means that a digital print process can not fully match a Pantone colour. The digital print will always be an approximation and the process for colour matching tends to be an iterative process depending on the colour content of the artwork file supplied. We cannot add pigment or medium to strengthen, change or weaken ink when printing digital label colours and densities unlike conventional high volume flexographic presses using expensive printing plates to produce high label volumes where ink can be adjusted on press.

An important factor affecting colour matching is the lighting conditions under which labels are viewed and so we need to be careful that when assessing printed label colours, the labels are viewed under correct lighting conditions. If a printed labels colour is viewed under say a fluorescent light of incomplete white light wave content, then because not all white light wavelengths enter the digital dot a condition called metamerism can cause the viewed colour to be different to the colour perceived when viewed in white light of adequate intensity. This explains why people often take a garment to the window to see the colour in daylight for example.

The relationship between CMYK and RGB is another issue to address where the label designer will create the label artwork on a computer which is viewed through its monitor where the colour gamut in RGB is bright and backlit on the screen. Once the artwork file is converted to a CMYK print file and printed on self adhesive label materials which all have different finishes, the resulting colour gamut printed by mixing CMYK dots in proportion to the file is smaller than the RGB gamut viewed on a monitor so it is important where colour matters in detail to see a printed proof of new designs wherever possible.

Our digital label print process enables us to print press proofs of your designs, using our production presses, onto production standard label stock and finish. In this way you can access a CMYK printed label that you can cut and apply and approve without buying production quantities of labels. Approved press proofs then become our contract standard to match. For new artwork, the printed label press proof maybe the first time the designer has seen the printed version of their design.

Digitally printed labels offer a cost effective and timely solution for small run customised labels and many label designers are engaging with digital label printing to offer their customers these advantages.

In practical terms the issue of colour matching is rarely discussed but could be an issue particularly when trying to match a previous printed colour sample that may have shifted from the design file content over time.

Whatever label printing process is used, colour matching of the printed result to a target or printed label standard is usual and needs to be managed by all involved in the chain of design and production of the label.

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