Appearance modelling and spectral proofing with fluorescing substrates
Partner: HIG, Norway
Fellow researcher: Ludovic Gustafsson Coppel
Supervisor: Prof. Jon Yngve Hardeberg
Calibration of printing system requires a printer model that predicts the colour of the print from the amount and distribution of the ink on top of the paper. Traditional colorimetric workflows aim at reproducing prints that best match an image described in a three-dimensional colour space (RGB or CIELAB) under one specific illuminantion (e.g. daylight). Thanks to metamerism, two different reflectance spectra can give the same appearance in one illumination. However, if the illuminant is changed, the perceived colour difference may get significantly large. Spectral workflows on the other hand require spectral images as input but aim at controlling the appearance of prints in different illuminants. This is of particular interest in some applications such as for example proofing, textile and furniture catalogues or paint swatch books to ensure a colour match no matter of the illumination under which they are used. Several applications require to take fluorescence into account. This includes of course proofing of fluorescing prints but also spot colour simulation and catalogues since almost all commercial paper substrates contain fluorescent whitening agents (FWA) to increase the whiteness of the paper. As soon as fluorescence is present, the spectral reflectance factor is no longer independent of the illumination making spectral printing an impossible task in terms of spectral match unless the printing substrate has the same fluorescing properties as the original.
The research project focused on developing physical models that predicts the spectral reflectance of halftone prints in illuminations with different amount of UV radiation and on developing spectral gamut mapping taking fluorescence into account. This involves determining the optical properties of multiple inks as well as their mixture and/or superposition, modelling ink spreading and lateral light propagation, and developing fluorescence models that can be calibrated using conventional spectrophotometers operating only in the visible part of the electromagnetic spectrum. The main deliverable is a spectral gamut mapping and separation method that enables to assess the colour change due to fluorescence under different illuminants and contributes to spectral printing whenever the reproduction and/or the original is fluorescing. Moreover, taking into account the different fluorescent contributions in the separation step leads to significantly, though moderate, reduced colour mismatches under variant illuminants.
The results enable spectral colour prediction for a multi-channel printer/substrate combination, and to some extent predict the effects of a change of paper properties, ink or printing setting. Expected applications are within appearance proofing, i.e. to simulate the appearance of different products in different illuminations with multi-channel inkjet printers. The proposed models provides a better understanding of the reflectance from halftone prints that contributes to the development of physical models for simpler and faster printer calibration to different substrates.
Publication and Dissemination
- Coppel L., Andersson M., Norberg O. and Lindberg S. (2013), Impact of illumination spectral power distribution on radiance factor of fluorescing materials, in ‘Colour and Visual Computing Symposium (CVCS), 2013’, IEEE, p. 4.
- Coppel L. G. (2014), Lateral light propagation and angular variation of the reflectance of paper, SPIE Electronic Imaging, San Francisco, CA, USA.
- Slavuj R., Coppel L. G., Olen M. and Hardeberg J. Y. (2014), Estimating Neugebauer primaries for multi-channel spectral printing modelling, SPIE Electronic Imaging, San Francisco, CA, USA.
- Coppel L.G., (2014), Dot gain analysis from probabilistic spectral modelling of colour halftone, ‘Advances in Printing and Media Technology, Print and Media Research for the Benefit of Industry and Society’, IARIGAI print and media research, Swansea, UK.
- Coppel L.G., Le Moan S., Zˇitinski P. E., Slavuj R., Hardeberg J. Y. (2014), Next gener- ation printing – Towards spectral proofing, ‘Advances in Printing and Media Technology, Print and Media Research for the Benefit of Industry and Society’, IARIGAI print and media research, Swansea, UK.
- Coppel L.G., Sole A.S., Harderbeg J.Y., (2014), Colour Printing 7.0: Next Generation Multi-Channel Printing, IS&T 22nd Color and Imaging Conference, Boston (MA).
- Slavuj R., Coppel L.G., Hardeberg J.Y., (2015), Effect of ink spreading and ink amount on the accuracy of the Yule-Nielsen modified spectral Neugebauer model, SPIE Electronic Imaging, San Francisco, CA, USA.
- Le Moan, S. and Coppel, L. G. (2015) Perceived Quality of Printed Images on Fluo- rescing Substrates under Various Illuminations, in proceedings of the 16th International Symposium on Multispectral Color Science, AIC 2015 Mid-term meeting, Tokyo, May 2015, Color Science Association of Japan.
- Coppel L.G., Perception of whiteness difference under different illuminations and backgrounds, 28th Session of the CIE Manchester, UK.
- Coppel L.G., Johanson N., Neuman M., (2015), Angular dependence of fluorescence from turbid media, Opt. Express, 23(15): 19552 – 19564 v.
- Coppel L.G., Spectral gamut mapping and ink separation with fluorescing substrates, ‘Colour and Visual Computing Symposium (CVCS), 2015’, IEEE.
- Book chapter – Coppel L.G., Chapter 20: Theory, Modelling and Simulation of Printing, Book chapter in (Izdebska E. J. and Sabu T. Eds.) Printing on Polymers: Fundamentals and Applications, Elsevier 307 – 327.