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Influence of white versus black backing

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The graphic arts industry allows for several options when performing spectral measurements. ISO 13655 (“Graphic technology — Spectral measurement and colorimetric computation for graphic arts images”) has been revised recently in order to address those parameters. With respect to the backing material to be used, it stipulates requirements for both black and white backing material. Anyhow, since contract proofs nowadays are mostly created using a more or less opaque inkjet paper with a dedicated ink receiving layer and not the intended production stock, colour differences emerge if the production stock is not perfectly opaque. In other words, a contract proof that matches the appearance with usually less opaque offset print on e.g. white paper next to it, won’t match if both are placed over e.g. black backing.

An ideal solution would be using the same backing material throughout the entire workflow. This is technically not achievable since process control calls for black backing and prepress agencies require white backing. The black backer is needed to minimize the impact of back printing, the variability due to translucency effects and to prevent any contamination or dirt. The prepress agencies require a white backing for particular reasons. First, the printed product looks more colourful and vibrant on white backing than on black backing and therefore sells better. Second, ICC-profiles based on characterization data on white backing usually result in better separation results. For these and several other reasons typical characterization data such as FOGRA39 (representing offset printing according to ISO 12647-2, gloss or matt coated stock, screening according to 60/cm) have been created for the usage on white backing.

A conversion between white and black backing is strongly demanded especially by the printers who have to rely on proprietary means to correct the white backing proof readings in order to achieve black backing aim values for the production run.

In this research project different models, usually used for spectral prediction of single or multi-colour halftone prints, will be tested by means of their accuracy of converting colorimetrical data measured with one backing to the values equivalent to those resulting from a measurement on a different backing.  



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