SUBSTRATE FOR COLOUR PROOFING

Print serves the purpose of exchanging information about a particular product, right ? It's no secret that any printing process is a marriage between ink and substrate. Substrate is a base material onto which the design artwork is printed. There are many varieties of substrates, paper being the most widely used. The Print on the substrate is accountable for exchanging details about a product or a piece of information. And Colours are the language of the print. The desired colour balance on the substrate helps us to improve print quality thereby making it look more appealing which eventually increase sales. For conveying your message through the print, keeping colour consistent throughout the marketing channels is essential. A substantial way to achieve this level of colour accuracy is Colour Proofing.

In simple words, proof is the sample print before the final print. Colour Proofing has evolved progressively. The print enthusiasts have realized it's significance and that how substrate plays a major role in determining the colour proof. Proofing not only help printers gain optimal visual print enhancement but also helps to avoid errors, imposition issues, improper registration etc. Also who wouldn't like to save the cost of the final print while achieving all these goals, right !? Colour proofing is the pathway. Verbalising technically, proofs help printers minimize the colour difference between reference and sample print. It's called as ΔE (delta E) of the CIELAB colour space. The smaller ΔE, the better and the best when ΔE < 3. Coming back to substrates, proof should communicate colour result on not just one but different substrates as well. Substrate characteristics namely cast, different paper batches, white point, influence the final print. For example, a 100% cyan patch will look quite different if it's printed on yellowish newsprint. And the same when printed on matte or gloss substrate will look different. In a nutshell, we may say that patch is 100% cyan in both cases but perceived colours are different. Hence colour is calibrated according to substrate while proofing. Do keep in mind however "Preservation of colour scheme while changing the substrate."

Fig :- Proof image with colour print production when printed on neutral white substrate

Substrate lightness (white point) plays a major role in proofing. With the help of Spectral Power Distribution (SPD), spectral data of substrates can be transformed into colourimetric values. Matching source white point to destination white point is quite crucial for substrates. Even the relevant psychometric tests along with technical experiments convey the same. The cognation established is that Neutral white substrate yield least colour difference. Another approach is SCCA (Substrate corrected colourimetric aims). Standard colour profile is revised using SCCA and this approach reduces colour difference to a greater extent. Adjusting colour temperature, brightness and monitoring display calibration, characterisation results in more accurate prints. Replacement of coated proofing substrate to revised SCCA substrate has been proven right. When your device is calibrated according to the proofing software (by taking substrate properties into consideration), one can achieve target profile more easily.

Fig :- Samples printed with Revised SCCA

Substrates are literally incomplete without coatings. They're known to accelerate drying time, reduce roughness thereby resulting in smooth print finish. The matte and gloss coatings can change the final overall appearance. Gloss yields least surface roughness where as higher amount of matte coating results in higher colour difference while proofing because of the large particle size. Black or the Key colour among CMYK yields maximum colour difference when printed on matte surface.

Fig. :- CMYKRGB colour gamut

Other than these factors, colour mode is also a governing aspect for colour proofing. Proofing when done with just CMYK colour mode generates more colour difference, whereas when done with CMYKRGB, it is less. RGB stands for Red, Green, Blue and are used for digital works. CMYK stands for Cyan, Magenta, Yellow, Black. They are process colours used for commercial printing. They yield less vibrant colours as compared to RGB no matter what substrate you’re using. One can achieve many more colours in RGB than just in CMYK. Reason is RGB gamut is immensely larger than CMYK. This eventually results in better proofing and less colour difference. RGB colour gamut attributes to this optimization. Last but not the least, the predominant factor is soft proofing substrate. Amongst the varieties of substrates, Newsprint produces smaller colour gamut which is a production substrate. Production substrates are used for commercial printing in printing press. Proofing substrates are used in soft proofing where the devices are calibrated. Production substrates should not be used for soft proofing. One should always use substrates designated specially for a particular process and should not confuse between the two. Only Proofing substrates should be used while proofing to obtain more colour precise prints. Thus, even small parameters like substrate coating, colour mode, colourimetric values can bring a colour shift while proofing to a greater extent.

So what, do substrates genuinely matter while colour proofing? I hope until now you must have got the answer. Of course, there are other requisites too for obtaining a good quality print. But you just can’t deny the paramountcy of Substrates for Colour Proofing. I consider myself fortunate enough to be a part of this industry and I hope you witness the best print experience in your press or academics. Thank you!

Riya Palhade

TE Printing Engg.

REFERENCES

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5. Lewis @ Print4uk. (2019, December 11). How the printing substrate changes the ink colour?– Print4UK Digital Print. Print4UK. Retrieved April 29, 2021, from https://print4uk.com/digital-printing-london/technical/how-the-printingsubstrate-changes- the-ink-colour/

6. Baah, K., Green, P., & Pointer, M. (2013, February). Perceived acceptability of colour matching for changing substrate white point. In Colour Imaging XVIII: Displaying, Processing, Hardcopy, and Applications (Vol. 8652, p. 86520Q). International Society for Optics and Photonics.

7. Ge, J., Fang, E., & Tian, D. (2019). Research on the Soft Proofing Technology Based on Substrate-Corrected Colorimetric Aims. In Advances in Graphic Communication, Printing and Packaging (pp. 120-126). Springer, Singapore.

8. Karlovic, I. (2011). The Influence of the Surface Roughness of Aqueous Coated Samples and the Particle Size of the Coatings on the Reflection and Colourimetric Values of Offset Printed Samples/Igor Karlovic, Ivana Tomic, Ivana Rilovski, Dragoljub Novakovic, Milica Vasic Vucinic, Uranija Kozmidis Luburic. International Circular of Graphic Education and Research. —Stuttgart: ICEI, 18-29.

9. Coppel, L. G., Le Moan, S., Elıas, P. Z., Slavuj, R., & Harderberg, J. Y. (2014). Next generation printing-Towards spectral proofing. Advanced in Printing and Media Technology, 41, 19-24

10. Johansson, N. (2009). Printing colour hard proofs using EFI Colorproof XF v. 3.1 and Photoshop CS3, and production substrates.

11. GeeksforGeeks. (2020, November 24). Differences between RGB and CMYK color schemes. https://www.geeksforgeeks.org/differences-between-rgb-and-cmyk-color-schemes/

12. Hook, W. (2018, January 22). PrintSouth Printing : blog. PrintSouth. https://www.myprintsouth.com/blog.html/article/2018/01/22/designing-for-print-rgb-vs-cmyk