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Angular dependent reflectance spectroscopy of RGBW pigments
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-0983-260x
University of the West of England, United Kingdom.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-5966-590x
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2022 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Traditional printing relies primarily on subtractive color mixing techniques. In this case, optical color mixing is achieved by one of the established halftoning methods that use Cyan, Magenta, Yellow and Black (CMYK) primaries on a reflective white substrate. The reason behind the subtractive color mixing in printing is the high absorbance of available pigments used in inks. A new type of mica-based pigments that exhibit high reflectivity at Red, Green, Blue and White (RGBW) spectral bands was recently introduced by Merck (SpectravalTM). Printing with RGBW primaries on black background allows additive color mixing in prints. While offering excellent color depth, the reflected spectra of such pigments vary with the angles of incidence and observation. As a result, new approaches in modelling the appearance of prints as well as strategies for color separation and halftoning are needed. The prior optical characterization of the reflective inks is an essential first step. For this purpose, we have used SpectravalTM pigments to prepare acrylic based inks, which we applied on glass slides by screen printing. In this work, we measured the relative spectral bidirectional reflection distribution of Red, Green, Blue and White reflective inks. The measurements were conducted on an experimental set up consisting of a goniometer, spectrometer, and a xenon light source. Based on the measurements, we simulate the reflectance spectra under diffuse illumination and demonstrate ratios of red, green, and blue spectral components for different observation angles of individual inks and their combinations.

Place, publisher, year, edition, pages
2022.
Keywords [en]
RGB printing, BRDF, spectroscopy, special effect inks
National Category
Media Engineering
Identifiers
URN: urn:nbn:se:liu:diva-189566OAI: oai:DiVA.org:liu-189566DiVA, id: diva2:1706599
Conference
48th Iarigai conference, Greenville SC, USA, Sept. 19-21 2022
Available from: 2022-10-26 Created: 2022-10-26 Last updated: 2024-04-05Bibliographically approved
In thesis
1. Modelling appearance printing: Acquisition and digital reproduction of translucent and goniochromatic materials
Open this publication in new window or tab >>Modelling appearance printing: Acquisition and digital reproduction of translucent and goniochromatic materials
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Colour perception is fundamental to our everyday experiences, allowing us to communicate and interpret visual information effectively. Yet, replicating these experiences accurately poses a significant challenge, particularly in the context of full-colour 3D printing. Advances in this field have revolutionised the fabrication of customised prosthetic body parts, such as eyes, teeth, and skin features, with profound implications for medical and aesthetic applications.

The key to successful 3D printing lies in the digital preview of objects before fabrication, enabling users to assess colour reproduction and quality. However, accurately representing colour in a digital environment is complex, as it depends on numerous factors, including illumination, object shape, surface properties, scene context, and observer characteristics. Traditional methods of previewing conventional 2D prints overlook this complexity.

This thesis addresses this challenge by focusing on two types of materials: semitransparent polymers commonly used in 3D printing, and goniochromatic colorants employed in printing to introduce unique effects unattainable with conventional inks for 2D printing. For semitransparent materials, we developed an empirical function to represent colour based on sample thickness, enabling efficient digital representation. Additionally, we adapted a colour measuring device to identify two key material parameters, absorption and scattering coefficients, essential for accurate colour reproduction.

Goniochromatic materials, such as thin film-coated mica particles, are slightly more complicated and less predictive in terms of their final colour appearance. Although not yet used in 3D printing, these particles used in conventional printing introduce colour variation while rotating the print. We found that goniochromatic properties can be expressed with an empirically found function after collecting angle-dependent light reflecting properties of the sample. We used this function and showed how prints with goniochromatic materials can be efficiently previewed on a computer monitor.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2024. p. 66
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2379
Keywords
Material appearance, 3D printing, Goniochromatism, Translucency
National Category
Media Engineering
Identifiers
urn:nbn:se:liu:diva-202036 (URN)10.3384/9789180755573 (DOI)9789180755566 (ISBN)9789180755573 (ISBN)
Public defence
2024-05-03, K3, Kåkenhus, Campus Norrköping, Norrköping, 09:15 (English)
Opponent
Supervisors
Note

Funding agency: The Marie Skłodowska-Curie Actions Innovative Training Network

Available from: 2024-04-05 Created: 2024-04-05 Last updated: 2024-05-06Bibliographically approved

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Pranovich, AlinaNyström, DanielValyukh, Sergiy

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