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  • 1.
    Bohlin, Erik
    et al.
    Karlstad Universitet.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Johansson, Caisa
    Karlstads Universitet.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Modelling of brightness decrease in coated cartonboard as an effect of calendering: Microroughness and effective refractive index aspects2010In: 11th Advanced Coating Fundamentals Symposium Proceedings: The Latest Advances in Coating Research and Development, Norcross, GA, USA: TAPPI Press, 2010, 51-65 p.Conference paper (Refereed)
    Abstract [en]

    Calendering of coated paper leads to a brightness decrease. The mechanism for this is not clear, although it has been discussed in the past. One common explanation is that the porosity of the coating layer decreases and hence scattering. By comparing simulated and measured results this paper shows that modifications of the surface properties account for the brightness decrease of GCC coated substrates with calendering. The effect of a deformable cartonboard substrate is investigated here and compared to a less deformable plastic film substrate. From simulations based on a two-layer Kubelka-Munk model, it is shown that the brightness decrease of the cartonboard due to calendering has a negligible contribution to the brightness decrease of the coated cartonboard. The brightness decrease was similar for coated plastic film and coated cartonboard. The thickness of GCC coated plastic films was not affected by calendering irrespectively of the pigment and latex size distribution. Monte Carlo light scattering simulations, taking into account the measured decrease of surface microroughness and increased effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease of the GCC coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It is also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not.

  • 2.
    Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Modelling the effect of simultaneous contrast on perceived whiteness2008In: 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 (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.

  • 3.
    Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Lindberg, S
    Rydefalk, S
    Whiteness assessment of paper samples at the vicinity of the upper CIE whiteness limit2007In: 26th Session of the CIE, 2007Conference paper (Refereed)
  • 4.
    Edström, Per
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Bohlin, Erik
    Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Andersson, Caisa
    Characterization and modelling of the effect of calendering on coated polyester film2009In: Advances in Printing and Media Technology, vol 36, International Association of Research Organizations for the Information, Media and Graphic Arts Industrie (IARIGAI), 2009Conference paper (Refereed)
  • 5.
    Edström, Per
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Open PaperOpt – A Monte Carlo Simulation Tool for Simulating Light Scattering in Paper and Print2010Report (Other academic)
    Abstract [en]

    The Kubelka-Munk model and extensions thereof are extensively used in product development, thanks to their simplicity and the fact that they are invertible. However, their explanative power is limited to distinguishing processes that affect scattering properties from those that affect absorption properties, an example being the frequently observed decrease of the scattering coefficient with calendering. Better understanding of how internal structural changes affect the optical properties requires modelling the composite structure of a paper layer. We propose a modular object-oriented Open Source Monte Carlo simulation platform, Open PaperOpt, which allows different geometrical representations of the inner paper structure. The proposed file formats open for a standardisation that facilitates data exchange between different simulation tools and measuring instruments, and supports a broad dissemination of the simulation software.

  • 6.
    Granberg, Hjalmar
    et al.
    Innventia AB.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Eita, M.
    Innventia AB, Box 5604, 104 86 Stockholm, Sweden.
    de Mayolo, E. A.
    Innventia AB, Box 5604, 104 86 Stockholm, Sweden.
    Arwin, Hans
    Innventia AB, Box 5604, 104 86 Stockholm, Sweden.
    Wågberg, Lars
    Innventia AB, Box 5604, 104 86 Stockholm, Sweden.
    Dynamics of moisture interaction with polyelectrolyte multilayers containing nanofibrillated cellulose2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 27, no 2, 496-499 p.Article in journal (Refereed)
    Abstract [en]

    Recent findings have shown that it is possible to use the Layer-by-Layer technique to create nanofibrillated cellulose / polyethyleneimine interference films whose colour change with relative humidity. This study uses different optical models to describe spectral ellipsometry measurements data of interference films and how the film properties alter in dry and humid environments. The results indicate that water condensation initially is filling the surface pores within seconds whereas relaxation of the film to adjust to the added water is a slower process that reaches a steady state after ≈20 min. The maximum swelling ratio of the LbL films is almost independent of the number of layers within the film, but decreases considerably by crosslinking via heat treatment. The films show a distinct birefringence with optical axis perpendicular to the surface. Analysis of the moisture response with different optical models indicates that the films swell uniformly in the thickness direction with no separate water film on top. The results provide important understanding for the design of NFC based LbL films for visual moisture sensors and interactive security paper. 

  • 7.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Measuring and producing high perceived whiteness2011In: Paper Technology, ISSN 0306-252X, Vol. 52, no 1, 15-17 p.Article in journal (Other academic)
  • 8.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Perception and measurement of the whiteness of papers with different gloss and FWA amount2009In: Advanced in Printing and Media Technology, vol 36, International Association of Research Organizations for the Information, Media and Graphic Arts Industrie (IARIGAI), 2009Conference paper (Refereed)
    Abstract [en]

    The effect of mean gloss level on perceived whiteness was evaluated by magnitude estimation and pair wisecomparison of papers with varying shades and gloss levels. The samples were printed on substrates ofdifferent gloss to target L*a*b* values measured under a light booth illumination having a 5000 K correlatedcolour temperature. Observers were able to rate the whiteness of the samples with large mean glossdifferences in the 5000 K illumination and in the same illumination with an additional UV lamp. The CIEwhiteness equation predicted well the perceived whiteness in both illuminations and the mean gloss level hadno significant effect on perceived whiteness. This means that the CIE whiteness equation can be used tocompare the perceived whiteness of papers having very different mean gloss levels. However, due to thedifferent amount of fluorescent whiteness agents (FWA) in the papers, the perceived whiteness predictionwas only valid when the measurement was performed under the same illumination as for the visualevaluations. Typical indoor illumination with florescent light tubes contains much less UV than the D50 or Cilluminants. The instrumental whiteness differences due to mean gloss and instrument geometry werenegligible compared to the effect of the UV content of the illumination.

  • 9.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Quantum efficiency of fluorescent dyesin different furnishesManuscript (preprint) (Other academic)
    Abstract [en]

    A recently proposed model for the radiative properties of optically thick fluorescentturbid media of finite thickness (Kokhanovsky, JOSA A, 26(8), p1896) is successfullyapplied to uncoated papers produced at different thicknesses. It is found that thequantum efficiency of the FWA is almost independent of the fibre type, FWA type,FWA concentration and filler additive concentrations used in this study. The scatteringcoefficient is however dependent on the FWA concentration. The absorptioncoefficient depends on the adsorption of the FWA in the furnish and is function ofthe sample thickness and of the FWA type, at equal amount of FWA used in the papermakingprocess. The results open for a estimation of the model parameters asfunction of the FWA concentration and furnish. This is necessary in order to use themodel for optimizing fluorescence in the paper and textile industries.

  • 10.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Whiteness and Fluorescence in Layered Paper and Board: Perception and Optical Modelling2012Doctoral 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.

  • 11.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Whiteness and Fluorescence in Paper: Perception and Optical Modelling2010Licentiate 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 includes psycho-physical 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. The standardised and widely used CIE whiteness equation is first tested on commercial office papers with visual evaluations by different panels of observers, and improved models are validated. Simultaneous contrast effects, known to affect the appearance of coloured surfaces depending on the surrounding colour, are shown to significantly affect the perceived whiteness. A colour appearance model including simultaneous contrast effects  (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. A recently proposed 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 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 quantum efficiency of two different fluorescent whitening agents (FWA) in plain paper is rather constant with FWA type, FWA concentration, filler content, and fibre type. Hence, the fluorescence efficiency 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. In addition, a modular Monte Carlo simulation tool, Open PaperOpt, is developed to allow future spatial- and angle-resolved particle level light scattering simulation.

     

  • 12.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Determination of quantum efficiency in fluorescing turbid media2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 17, 2784-2792 p.Article in journal (Refereed)
    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.

  • 13.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Kinnunen, Jussi
    Univ Eastern Finland, Dept Math & Phys, FI-80101 Joensuu, Finland.
    Limitations of the efficiency of fluorescent whitening agents in uncoated paper2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 26, no 3, 319-328 p.Article in journal (Refereed)
    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.

  • 14.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Fluorescence model for multi-layer papers using conventional spectrophotometers2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 27, no 2, 418-425 p.Article in journal (Refereed)
    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.

  • 15.
    Gustafsson Coppel, Ludovic
    et al.
    Norwegian Colour and Visual Computing Laboratory, Gjøvik University College, Gjøvik, Norway.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Norberg, Ole
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Lindberg, S.
    Innventia AB, Stockholm, Sweden.
    Impact of illumination spectral power distribution on radiance factor of fluorescing materials2013In: 2013 Colour and Visual Computing Symposium, CVCS 2013, 2013, Art. no. 6626275- p.Conference paper (Refereed)
    Abstract [en]

    The spectral radiance factor and thereby the appearance of fluorescing material is known to depend strongly on the spectral power distribution (SPD) of the illumination in the fluorophore's excitation wavelength band. The present work demonstrates the impact of the SPD in the fluorescence emission band on the total radiance factor. The total radiance factor of a fluorescing paper is measured in three different illuminations. The presence of peaks in the SPD of fluorescent light tubes dramatically decreases the luminescent radiance factor. This effect will impact the appearance of fluorescing media under illuminations with large variation in SPD, which includes recent LED illuminations. © 2013 IEEE.

  • 16.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Open source Monte carlo simulation platform for particle level simulation of light scattering from generated paper structures2009In: Papermaking Research Symposium, 2009Conference paper (Refereed)
  • 17.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Extension of the Stokes equation for layered constructions to fluorescent turbid media2012In: Journal of the Optical Society of America A, ISSN 0740-3232, Vol. 29, no 4, 574-578 p.Article in journal (Refereed)
    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.

  • 18.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Lateral light scattering in paper - MTF simulation and measurement2011In: Optics Express, ISSN 1094-4087, Vol. 19, no 25, 25181-25187 p.Article in journal (Refereed)
    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.

  • 19.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Norberg, Ole
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Lindberg, Siv
    Innventia AB.
    Paper whiteness and its effect on perceived image quality2010In: Final Program and Proceedings - IS and T/SID Color Imaging Conference, The Society for Imaging Science and Technology, 2010, Vol. 50, no 17, 62-67 p.Conference paper (Refereed)
    Abstract [en]

    Whiteness is a commercially important characteristic of paper and board, although its perception depends on many factors that often are neglected by instrumental measurements. High whiteness improves the contrast of printed areas and increases the number of reproducible colours, but few quantitative studies have been published. In this paper, we report just-noticeable image quality difference (JND) from pair wise comparisons of images printed on paper substrate of different shades and whiteness. The JND was estimated to approximately 15 CIE whiteness, for the images and whiteness levels in this study, implying that a large substrate whiteness difference is required to get a significant visual impact on image quality. Unlike previous studies limited to colour rendering issues, the influence of the substrate’s shade as a surrounding frame to the images was also investigated here. It was found that the surrounding frame did not have a significant impact on image quality, when the images had an inherent dim background around the objects in the image. However, floating images in which the image objects are adjacent to the unprinted substrate would need further attention, since their perceived image quality seemed to depend both on the colour reproduction related to whiteness and shade, and on the contrast between the image and the substrate.

  • 20.
    Linder, Tomas
    et al.
    Department of Computer Science, Electrical and Space Engineering Luleå University of Technology.
    Löfqvist, Torbjörn
    Department of Computer Science, Electrical and Space Engineering Luleå University of Technology.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Lateral light scattering in fibrous media2013In: Optics Express, ISSN 1094-4087, Vol. 21, no 6, 7835-7840 p.Article in journal (Refereed)
    Abstract [en]

    Lateral light scattering in fibrous media is investigated by computing the modulation transfer function (MTF) of 22 paper samples using a Monte Carlo model. The simulation tool uses phase functions from infinitely long homogenous cylinders and the directional inhomogeneity of paper is achieved by aligning the cylinders in the plane. The inverse frequency at half maximum of the MTF is compared to both measurements and previous simulations with isotropic and strongly forward single scattering phase functions. It is found that the conical scattering by cylinders enhances the lateral scattering and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. However, it does not fully reach the levels of lateral scattering observed in measurements. It is argued that the hollow lumen of a wood fiber or dependent scattering effects must be considered for a complete description of lateral light scattering in paper.

  • 21.
    Namedanian, Mahziar
    et al.
    Department of Science and Technology, Linköping University, Norrköping, Sweden .
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Gooran, Sasan
    Department of Science and Technology, Linköping University, Norrköping, Sweden .
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Kolseth, Petter
    Nsieme Consulting, Sweden .
    Koh, Wei
    Analysis of Optical and Physical Dot Gain by Microscale Image Histogram and Modulation Transfer Functions2013In: Journal of Imaging Science and Technology, ISSN 1062-3701, Vol. 57, no 2, 020504-1-020504-5 p.Article in journal (Refereed)
    Abstract [en]

    The color of a print is affected by ink spreading and lateral light scattering in the substrate, making printed dots appear larger. Characterization of physical and optical dot gain is crucial for the graphic arts and paper industries. We propose a novel approach to separate physical from optical dot gain by use of a high-resolution camera. This approach is based on the histogram of microscale images captured by the camera. Having determined the actual physical dot shape, we estimate the modulation transfer function (MTF) of the paper substrate. The proposed method is validated by comparing the estimated MTF of 11 offset printed coated papers to the MTF obtained from the unprinted papers using measured and Monte Carlo simulated edge responses.

  • 22.
    Neuman, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Point spreading in turbid media with anisotropic single scattering2011In: Optics Express, ISSN 1094-4087, Vol. 19, no 3, 1915-1920 p.Article in journal (Refereed)
    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.

  • 23.
    Neuman, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Norberg, Ole
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Angular Variations of Color in Turbid Media – the Influence of Bulk Scattering on Goniochromism in Paper2010In: 5th European Conference on Colour in Graphics, Imaging, and Vision and 12th International Symposium on Multispectral Colour Science 2010, CGIV 2010/MCS'10, 2010, 407-413 p.Conference paper (Refereed)
    Abstract [en]

    The angular variations of color of a set of paper samples are  experimentally assessed using goniophotometric measurements.  The corresponding simulations are done using a radiative transfer based simulation tool, thus considering only the contribution  of bulk scattering to the reflectance. It is seen that measurements  and simulations agree and display the same characteristics, with  the lightness increasing and the chroma decreasing as the observation  polar angle increases. The decrease in chroma is larger  the more dye the paper contains. Based on previous results about  anisotropic reflectance from turbid media these findings are explained.  The relative reflectance in large polar angles of wavelengths  with strong absorption is higher than that of wavelengths  with low absorption. This leads to a loss of chroma and color information  in these angles. The increase in lightness is a result  of the anisotropy affecting all wavelengths equally, which is the  case for transmitting media and obliquely incident illumination.  The only case with no color variations of this kind is when a nonabsorbing,  non-transmitting medium is illuminated diffusely. The  measured and simulated color differences are clearly large, and  it is an open issue how angle resolved color should be handled  in standard color calculations.

  • 24.
    Neuman, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    G. Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Angle resolved color of bulk scattering media2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 36, 6555-6563 p.Article in journal (Refereed)
    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.

  • 25.
    Neuman, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    A partial explanation of the dependence between light scattering and light absorption in the Kubelka-Munk model2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 27, no 2, 426-430 p.Article in journal (Refereed)
    Abstract [en]

    The Kubelka-Munk scattering and absorption coefficients of a set of paper samples are assessed using reflectance measurements in d/0 geometry. The coefficients display the widely studied dependence between light scattering and light absorption, since the light scattering coefficient decreases in regions of high absorption. It is shown using general radiative transfer theory that part of this dependence can be explained and eliminated by taking into account the geometry of the d/0 instrument and the single scattering anisotropy, thus capturing the angular variations of the light reflected from the samples. These findings allow the papermaker to better predict the reflectance from mixtures of pulps, fillers, dye, and FWA, and to better evaluate bleaching efforts. 

1 - 25 of 25
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