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Angular Variations of Color in Turbid Media – the Influence of Bulk Scattering on Goniochromism in Paper
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.ORCID iD: 0000-0002-0529-1009
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
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2010 (English)In: 5th European Conference on Colour in Graphics, Imaging, and Vision and 12th International Symposium on Multispectral Colour Science 2010, CGIV 2010/MCS'10, 2010, p. 407-413Conference paper, Published 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.

Place, publisher, year, edition, pages
2010. p. 407-413
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:miun:diva-11758Scopus ID: 2-s2.0-78649358316ISBN: 978-161738889-7 (print)OAI: oai:DiVA.org:miun-11758DiVA, id: diva2:326538
Conference
5th European Conference on Colour in Graphics, Imaging, and Vision and 12th International Symposium on Multispectral Colour Science 2010, CGIV 2010/MCS'10; Joensuu; 14 June 2010 through 17 June 2010; Code 82712
Funder
Available from: 2010-06-23 Created: 2010-06-23 Last updated: 2011-01-25Bibliographically approved
In thesis
1. Angle Resolved Light Scattering in Turbid Media: Analysis and Applications
Open this publication in new window or tab >>Angle Resolved Light Scattering in Turbid Media: Analysis and Applications
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Light scattering in turbid media is essential for such diverse application areas as paper and print, computer rendering, optical tomography, astrophysics and remote sensing. This thesis investigates angular variations of light reflected from plane-parallel turbid media using both mathematical models and reflectance measurements, and deals with several applications. The model of most widespread use in industry is the Kubelka-Munk model, which neglects angular variations in the reflected light. This thesis employs a numerical solution of the angle resolved radiative transfer problem to better understand how the angular variations are related to medium properties. It is found that the light is reflected anisotropically from all media encountered in practice, and that the angular variations depend on the medium absorption and transmittance and on the angular distribution of the incident light. If near-surface bulk scattering dominates, as in strongly absorbing or highly transmitting media or obliquely illuminated media, relatively more light is reflected in large polar (grazing) angles. These results are confirmed by measurements using a set of paper samples. The only situation with isotropic reflectance is when a non-transmitting, non-absorbing medium is illuminated diffusely. This is the only situation where the Kubelka-Munk model is exactly valid. The results also show that there is no such thing as an ideal bulk scattering diffusor, and these findings can affect calibration and measurement procedures defined in international standards.The implications of the presented results are studied for a set of applications including reflectance measurements, angle resolved color and point spreading. It is seen that differences in instrument detection and illumination geometry can result in measurement differences. The differences are small and if other sources of error - such as fluorescence and gloss - are not eliminated, the differences related to instrument geometry become difficult to discern. Furthermore, the angle resolved color of a set of paper samples is assessed both theoretically and experimentally. The chroma decreases and the lightness increases as the observation polar angle increases. The observed differences are clearly large, and it is an open issue how angle resolved color should be handled. Finally, the dependence of point spreading in turbid media on the medium parameters is studied. The asymmetry factor is varied while maintaining constant the optical response in a standardized measurement geometry. It is seen that the point spreading increases as forward scattering becomes more dominant, and that the effect is larger if the medium is low-absorbing with large mean free path. A generic model of point spreading must therefore capture the dependence on all of these medium parameters.This thesis shows that turbid media reflect light anisotropically, and angle resolved radiative transfer models are therefore necessary to capture this. Using simplified models can introduce errors in an uncontrolled manner. The results presented potentially have consequences for all applications dealing with light scattering, some of which are studied here.

Place, publisher, year, edition, pages
Härnösand: Mid Sweden University, 2011. p. 17
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 56
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:miun:diva-13154 (URN)978-91-86694-22-7 (ISBN)
Presentation
2011-02-16, O111, Gånsviksvägen 2, Härnösand, 10:00 (English)
Opponent
Supervisors
Available from: 2011-01-25 Created: 2011-01-25 Last updated: 2011-01-25Bibliographically approved

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Neuman, MagnusEdström, PerAndersson, MattiasCoppel, LudovicNorberg, Ole

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