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Whiteness and Fluorescence in Layered Paper and Board: Perception and Optical Modelling
Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. This involves psychophysical modelling of perceived whiteness from measurable light reflectance properties, and physical modelling of light scattering and fluorescence from the paper composition.

Existing models are first tested and improvements are suggested and evaluated. A colour appearance model including simultaneous contrast effects (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. An extension of the Kubelka-Munk light scattering model including fluorescence for turbid media of finite thickness is successfully tested for the first time on real papers. It is extended to layered constructions with different layer optical properties and modified to enable parameter estimation with conventional d/0° spectrophotometers used in the paper industry. Lateral light scattering is studied to enable simulating the spatially resolved radiance factor from layered constructions, and angle-resolved radiance factor simulations are performed to study angular variation of whiteness.

It is shown that the linear CIE whiteness equation fails to predict the perceived whiteness of highly white papers with distinct bluish tint. This equation is applicable only in a defined region of the colour space, a condition that is shown to be not fulfilled by many commercial office papers, although they appear white to most observers. The proposed non-linear whiteness equations give to these papers a whiteness value that correlates with their perceived whiteness, while application of the CIE whiteness equation outside its region of validity overestimates perceived whiteness.

It is shown that the fluorescence efficiency of FWA is essentially dependent only on the ability of the FWA to absorb light in its absorption band. Increased FWA concentration leads accordingly to increased whiteness. However, since FWA absorbs light in the violet-blue region of the electromagnetic spectrum, the reflectance factor decreases in that region with increasing FWA amount. This violet-blue absorption tends to give a greener shade to the paper and explains most of the observed greening and whiteness saturation at larger FWA concentrations. A red-ward shift of the quantum efficiency is observed with increasing FWA concentration, but this is shown to have a negligible effect on the whiteness value. The results are directly applicable to industrial applications for better instrumental measurement of whiteness and thereby optimising the use of FWA with the goal to improve the perceived whiteness.

Place, publisher, year, edition, pages
Sundsvall: annat förlag , 2012. , 158 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 138
Keyword [en]
Whiteness, Perception, Colour Appearance Modelling, Paper Optics, Light Scattering, Fluorescence, Lateral Light Scattering, White-Top Mottle, Kubelka-Munk, Radiative Transfer
National Category
Paper, Pulp and Fiber Technology Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:miun:diva-17782ISBN: 978-91-87103-50-6 (print)OAI: oai:DiVA.org:miun-17782DiVA: diva2:577815
Public defence
2013-01-23, Sal 0111, Mittuniversitetet, Holmgatan 10, Sundsvall, 10:31 (English)
Opponent
Supervisors
Projects
PaperOpt
Funder
The Knowledge FoundationVinnova
Available from: 2012-12-20 Created: 2012-12-17 Last updated: 2012-12-20Bibliographically approved
List of papers
1. Whiteness assessment of paper samples at the vicinity of the upper CIE whiteness limit
Open this publication in new window or tab >>Whiteness assessment of paper samples at the vicinity of the upper CIE whiteness limit
2007 (English)In: 26th Session of the CIE, 2007Conference paper, Published paper (Refereed)
National Category
Materials Engineering
Identifiers
urn:nbn:se:miun:diva-6824 (URN)6006 (Local ID)6006 (Archive number)6006 (OAI)
Available from: 2008-12-08 Created: 2008-11-02 Last updated: 2012-12-20Bibliographically approved
2. Modelling the effect of simultaneous contrast on perceived whiteness
Open this publication in new window or tab >>Modelling the effect of simultaneous contrast on perceived whiteness
2008 (English)In: Society for Imaging Science and Technology - 4th European Conference on Colour in Graphics, Imaging, and Vision and 10th International Symposium on Multispectral Colour Science, CGIV 2008/MCS'08, The Society for Imaging Science and Technology, 2008, 183-188 p.Conference paper, Published paper (Refereed)
Abstract [en]

The perceived colour from a surface does not only depend on its optical properties and the illumination. Several studies have demonstrated the simultaneous contrast effect that makes the appearance of coloured patches depend on neighbouring colours. In this study the perceived whiteness of white patches surrounded by induction fields of different shades was evaluated by asking observers to give a magnitude estimate of perceived whiteness of the patches in comparison to a white reference. The perceived whiteness of patches with identical tristimulus values was highly dependent on the shade of the induction field and the patch size did not significantly affect the perceived whiteness. The recent CIECAM02-m2 colour appearance model was tested together with two whiteness equations. A combination of ClECAM02-m2 and a non-linear whiteness equation defined in the whole colour space predicted much of the observed simultaneous contrast effect. However, the model performed better for dark induction fields than for light induction fields. The model rated patches surrounded by light blue and light yellow equally, whereas the observers clearly rated the patches with light yellow induction field as whiter than the patches with light blue induction field. A deeper analysis of the CIECAM02-m2 model indicated that the simultaneous contrast model used cannot accurately predict the change in hue for high lightness induction fields. A potential improvement for predicting contrast simultaneous effect would be to base the calculations not only on the difference between the induction field and the background, but on the difference between the patch stimulus and the induction field.

Place, publisher, year, edition, pages
The Society for Imaging Science and Technology, 2008
Keyword
simultaneous contrast effect, whiteness, colour appearance modelling, CIECAM02
National Category
Materials Engineering
Identifiers
urn:nbn:se:miun:diva-6825 (URN)2-s2.0-70349971071 (Scopus ID)6007 (Local ID)978-160560702-3 (ISBN)6007 (Archive number)6007 (OAI)
Conference
4th European Conference on Colour in Graphics, Imaging, and Vision and 10th International Symposium on Multispectral Colour Science, CGIV 2008/MCS'08; Terrassa; Spain; 9 June 2008 through 13 June 2008; Code 77574
Available from: 2008-12-08 Created: 2008-11-02 Last updated: 2016-09-26Bibliographically approved
3. Open source Monte carlo simulation platform for particle level simulation of light scattering from generated paper structures
Open this publication in new window or tab >>Open source Monte carlo simulation platform for particle level simulation of light scattering from generated paper structures
2009 (English)In: Papermaking Research Symposium, 2009Conference paper, Published paper (Refereed)
Keyword
light scattering, fluorescence, paper strucutre modelling
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-9122 (URN)978-951-27-1038-6 (ISBN)
Projects
PaperOpt
Available from: 2009-10-02 Created: 2009-06-09 Last updated: 2012-12-20Bibliographically approved
4. Determination of quantum efficiency in fluorescing turbid media
Open this publication in new window or tab >>Determination of quantum efficiency in fluorescing turbid media
2011 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 17, 2784-2792 p.Article in journal (Refereed) Published
Abstract [en]

A method is proposed to estimate the optical parameters in a fluorescing turbid medium with strong absorption for which traditional Kubelka–Munk theory is not applicable, using a model for the radiative properties of optically thick fluorescent turbid media of finite thickness proposed in 2009[J. Opt. Soc. Am. A26, 1896 (2009)JOAOD60740-323210.1364/JOSAA.26.001896]. The method is successfully applied to uncoated papers with different thicknesses. It is found that the quantum efficiency of fluorescent whitening agents (FWAs) is nearly independent of the fiber type, FWA type, FWA concentration, and filler additive concentration used in this study. The results enable an estimation of the model parameters as function of the FWA concentration and substrate composition. This is necessary in order to use the model for optimizing fluorescence in the paper and textile industries.

Keyword
fluorescence, turbid media, quantum efficiency, scattering, paper
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-15704 (URN)10.1364/AO.50.002784 (DOI)000291872800036 ()2-s2.0-79958796672 (Scopus ID)
Projects
PaperOpt
Available from: 2012-01-13 Created: 2012-01-13 Last updated: 2017-12-08Bibliographically approved
5. Limitations of the efficiency of fluorescent whitening agents in uncoated paper
Open this publication in new window or tab >>Limitations of the efficiency of fluorescent whitening agents in uncoated paper
2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 3, 319-328 p.Article in journal (Refereed) Published
Abstract [en]

The fluorescence efficiency of one fluorescent whitening agent (FWA) inuncoated and unfilled paper was characterised at different FWA concentrations. An extendedKubelka-Munk model proposed earlier by several authors was applied to quantify the effect onCIE whiteness of absorption of the FWA in the visible spectrum . At high FWA concentration,chemical interactions slightly modify the emission spectrum of the FWA, and the quantumefficiency depends on the FWA concentration. This effect has however a negligible effect onthe CIE whiteness for FWA concentrations used in practice. The overlap of the absorption andemission bands of the FWA is shown to be the main cause of greening (a shift of thechromaticity towards green) and saturation of the fluorescence effect. With increasing FWAconcentration, the positive effect of fluorescence is neutralised by the reduction of thereflectance factor in the violet-blue region of the spectrum induced by a significant absorptionof the FWA in that region.

Keyword
Fluorescence, paper, fluorescence whitening agents, greening, whiteness
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-12142 (URN)10.3183/NPPRJ-2011-26-03-p319-328 (DOI)000294524200010 ()2-s2.0-80052349477 (Scopus ID)
Projects
PaperOpt
Available from: 2010-10-18 Created: 2010-10-18 Last updated: 2017-12-12Bibliographically approved
6. Point spreading in turbid media with anisotropic single scattering
Open this publication in new window or tab >>Point spreading in turbid media with anisotropic single scattering
2011 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 3, 1915-1920 p.Article in journal (Refereed) Published
Abstract [en]

Point spreading is investigated using general radiative transfer theory. We find that the single scattering anisotropy plays a significant role for point spreading together with the medium mean free path, single scattering albedo and thickness. When forward scattering dominates, the light will on average undergo more scattering events to give a specific optical response in reflectance measurements. This will significantly increase point spreading if the medium is low absorbing with large mean free path. Any fundamental and generic model of point spreading must capture the dependence on all of these medium characteristics.

Place, publisher, year, edition, pages
OSA, 2011
Keyword
OPTICAL-PROPERTIES; PAPER; REFLECTANCE; MTF
National Category
Other Engineering and Technologies Computational Mathematics
Identifiers
urn:nbn:se:miun:diva-13113 (URN)10.1364/OE.19.001915 (DOI)000286807100026 ()21369006 (PubMedID)2-s2.0-79851482792 (Scopus ID)
Projects
PaperOptOptics of Paper and Print - Continuous Models
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2017-12-11Bibliographically approved
7. Lateral light scattering in paper - MTF simulation and measurement
Open this publication in new window or tab >>Lateral light scattering in paper - MTF simulation and measurement
2011 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 25, 25181-25187 p.Article in journal (Refereed) Published
Abstract [en]

The modulation transfer function (MTF) of 22 paper samples is computed using Monte Carlo simulations with isotropic or strongly forward single scattering. The inverse frequency at half maximum of the MTF (kp) is found inappropriate as a single metric for the MTF since it is insensitive to the shape of the modeled and simulated MTF. The single scattering phase function has a significant impact on the shape of the MTF, leading to more lateral scattering. However, anisotropic single scattering cannot explain the larger lateral scattering observed in paper. It is argued that the directional inhomogeneity of paper requires a light scattering model with both the phase function and scattering distances being dependent on the absolute direction.

Place, publisher, year, edition, pages
Optical Society of America, 2011
Keyword
scattering turbid media lateral scattering paper
National Category
Other Physics Topics Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-15014 (URN)10.1364/OE.19.025181 (DOI)000297702400033 ()2-s2.0-82955208266 (Scopus ID)
Projects
PaperOpt
Available from: 2011-12-02 Created: 2011-12-02 Last updated: 2017-12-08Bibliographically approved
8. Angle resolved color of bulk scattering media
Open this publication in new window or tab >>Angle resolved color of bulk scattering media
2011 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 36, 6555-6563 p.Article in journal (Refereed) Published
Abstract [en]

The angle resolved reflectance factor of matte samples is measured with a goniophotometer and simulated using radiative transfer theory. Both measurements and simulations display the same characteristic dependence of the reflectance factor on the observation angle. The angle resolved reflectance spectra are translated to CIELAB color coordinates and the angular color differences are found to be surprisingly large. A chromatic adaptation that is dependent on the observation angle is suggested, in which a nonabsorbing opaque medium is used as the reference white, and the angular color differences are then reduced. Furthermore, the use of an undyed paper as the reference white is evaluated. The angular lightness differences are then reduced further, but the angular differences in chroma are still large. It is suggested that smaller variations in perceived color could be explained by angle dependent chromatic adaptation and a limited sensitivity of the human visual system to changes in chroma.

Keyword
Angle resolved color; bulk scattering media
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-15157 (URN)10.1364/AO.50.006555 (DOI)000299166700002 ()2-s2.0-84255190004 (Scopus ID)
Projects
PaperOptOptics of paper and print: continuous models
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2017-12-08Bibliographically approved
9. Extension of the Stokes equation for layered constructions to fluorescent turbid media
Open this publication in new window or tab >>Extension of the Stokes equation for layered constructions to fluorescent turbid media
2012 (English)In: Journal of the Optical Society of America A, ISSN 0740-3232, Vol. 29, no 4, 574-578 p.Article in journal (Refereed) Published
Abstract [en]

Expressions relating the bispectral reflectance of a stack of n fluorescinglayers to each individual layer's reflectance and transmittance arederived. This theoretical framework is used together with recentlyproposed extensions of the Kubelka--Munk model to study the fluorescencefrom layered turbid media. For one layer over a reflecting background,the model is shown to give the same results as a previous model.The extension to n layers with different optical properties allowssimulating the bispectral reflectance from a pad of layered turbidmedia. The applicability of the model is exemplified with an optimizationof fluorophore distribution in layered turbid media.

Place, publisher, year, edition, pages
Optical Society of America, 2012
Keyword
Fluorescence; Multiple scattering; Turbid media; Color
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-16015 (URN)000302561500025 ()2-s2.0-84873472513 (Scopus ID)
Projects
PaperOpt
Available from: 2012-03-23 Created: 2012-03-23 Last updated: 2017-12-07Bibliographically approved
10. Fluorescence model for multi-layer papers using conventional spectrophotometers
Open this publication in new window or tab >>Fluorescence model for multi-layer papers using conventional spectrophotometers
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, 418-425 p.Article in journal (Refereed) Published
Abstract [en]

We present an extension of a Kubelka-Munk based fluorescence model in which we introduce an apparent scattering (SUV) and absorption (KUV) coefficient for all wavelengths below 400 nm. We describe a method for modelling the total radiance factor of multi-layer papers and for estimating the optical parameters (S, K and Q) of each layer. Assuming that the fluorescent whitening agent only absorbs below 400 nm, we are able to determine SUV, KUV and the apparent quantum efficiency, Q(UV,l) for 400 nm<l<700 nm, from spectral radiance measurements in the visual part of the electromagnetic spectrum. We test the proposed method on different layered constructions made of three individual pilot paper layers. The proposed method allows the papermaker to determine the illumination independent fluorescence characteristics of single- and multilayer paper layers using a conventional single-monochromator spectrophotometer operating in the visible part of the electromagnetic spectrum, and also to predict the radiance factor of fluorescing layered papers.

Keyword
Whiteness, Kubelka-Munk, Multi-layer, Fluorescence, Fluorescent whitening agents
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-16016 (URN)10.3183/NPPRJ-2012-27-02-p418-425 (DOI)000315696000034 ()2-s2.0-84865261999 (Scopus ID)
Projects
PaperOpt
Available from: 2013-04-04 Created: 2012-03-23 Last updated: 2017-12-07Bibliographically approved

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