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- Abedini, Fereshteh, 1989-
(author)
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2D and 3D Halftoning for Appearance Reproduction
- 2023
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Doctoral thesis (other academic/artistic)abstract
- The appearance of an object is determined by its chromatic and geometric qualities in its surrounding environment using four optical parameters: color, gloss, translucency, and surface texture. Reconstructing the appearance of objects is of great importance in many applications, including creative industries, packaging, fine-art reproduction, medical simulation, and prosthesis-making. Printers are reproduction devices capable of replicating objects’ appearance in 2D and 3D forms. With the introduction of new printing technologies, new inks and materials, and demands for innovative applications, creating accurate reproduction of the desired visual appearance has become challenging. Thus, the appearance reproduction workflow requires improvements and adaptations. Accurate color reproduction is a critical quality measure in reproducing the desired appearance in any printing process. However, printers are devices with a limited number of inks that can either print a dot or leave it blank at a specific position on a substrate; hence, to reproduce different colors, optimal placement of the available inks is needed. Halftoning is a technique that deals with this challenge by generating a spatial distribution of the available inks that creates an illusion of the target color when viewed from a sufficiently large distance. Halftoning is a fundamental part of the color reproduction task in any full-color printing pipeline, and it is an effective technique to increase the potential of printing realistic and complex appearances. Although halftoning has been used in 2D printing for many decades, it still requires improvements in reproducing fine details and structures of images. Moreover, the emergence of new technologies in 3D printing introduces a higher degree of freedom and more parameters to the field of appearance reproduction. Therefore, there is a critical need for extensive studies to revisit existing halftoning algorithms and develop novel approaches to produce high quality prints that match the target appearance faithfully. This thesis aims at developing halftoning algorithms to improve appearance reproduction in 2D and 3D printing. Contributions of this thesis in the 2D domain is a dynamic sharpness-enhancing halftoning approach, which adaptively varies the local sharpness of the halftone image based on different textures in the original image for realistic appearance printing. The results show improvements in halftone quality in terms of sharpness, preserving structural similarity, and decreasing color reproduction error. The main contribution of this thesis in 3D printing is extending a high quality 2D halftoning algorithm to the 3D domain. The proposed method is then integrated with a multi-layer printing approach, where ink is deposited at variable depths to improve the reproduction of tones and fine details. Results demonstrate that the proposed method accurately reproduces tones and details of the target appearance. Another contribution of this thesis is studying the effect of halftoning on the perceived appearance of 3D printed surfaces. According to the results, changing the dot placement based on the elevation variation of the underlying geometry can potentially control the perception of the 3D printed appearance. It implies that the choice of halftone may prove helpful in eliminating unwanted artifacts, enhancing the object’s geometric features, and producing a more accurate 3D appearance. The proposed methods in this thesis have been evaluated using different printing techniques.
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| 5. |
- Abedini, Fereshteh, et al.
(author)
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3D Halftoning based on Iterative Method Controlling Dot Placement
- 2020
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Conference paper (peer-reviewed)abstract
- Realistic appearance reproduction is of great importance in 3D printing’s applications. Halftoning as a necessary process in printing has a great impact on creating visually pleasant appearance. In this article, we study the aspects of adapting and applying Iterative Method Controlling Dot Placement (IMCDP) to halftone three-dimensional surfaces. Our main goal is to extend the 2D algorithm to a 3D halftoning approach with minor modifications. The results show high-quality reproduction for all gray tones. The 3D halftoning algorithm is not only free of undesirable artifacts, it also produces fully symmetric and wellformed halftone structures even in highlight and shadow regions.
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| 6. |
- Abedini, Fereshteh, et al.
(author)
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Structure-Aware Halftoning Using the Iterative Method Controlling the Dot Placement
- 2021
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In: Journal of Imaging Science and Technology. - : I S & T-SOC IMAGING SCIENCE TECHNOLOGY. - 1062-3701 .- 1943-3522. ; 65:6
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Journal article (peer-reviewed)abstract
- Many image reproduction devices, such as printers, are limited to only a few numbers of printing inks. Halftoning, which is the process to convert a continuous-tone image into a binary one, is, therefore, an essential part of printing. An iterative halftoning method, called Iterative Halftoning Method Controlling the Dot Placement (IMCDP), which has already been studied by research scholars, generally results in halftones of good quality. In this paper, we propose a structure-based alternative to this algorithm that improves the halftone image quality in terms of sharpness, structural similarity, and tone preservation. By employing appropriate symmetrical and non-symmetrical Gaussian filters inside the proposed halftoning method, it is possible to adaptively change the degree of sharpening in different parts of the continuous-tone image. This is done by identifying a dominant line in the neighborhood of each pixel in the original image, utilizing the Hough Transform, and aligning the dots along the dominant line. The objective and subjective quality assessments verify that the proposed structure-based method not only results in sharper halftones, giving more three-dimensional impression, but also improves the structural similarity and tone preservation. The adaptive nature of the proposed halftoning method makes it an appropriate algorithm to be further developed to a 3D halftoning method, which could be adapted to different parts of a 3D object by exploiting both the structure of the images being mapped and the 3D geometrical structure of the underlying printed surface.
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| 7. |
- Abedini, Fereshteh, et al.
(author)
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The Effect of Halftoning on the Appearance of 3D Printed Surfaces
- 2021
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Conference paper (peer-reviewed)abstract
- Managing the final appearance of 3D surfaces is an interesting and essential topic in 3D printing applications. Knowledge about the parameters which influence the 3D surface reproduction quality enables engineers to achieve the final appearance as accurately as designed. Many studies have been conducted to explore numerous parameters that affect the quality of 3D surface reproduction. This work contributes to verifying the role of halftoning in increasing the 3D surface visual quality and the control over the surface appearance of a 3D printed object. The results show that applying different halftones according to the geometrical characteristics of the 3D surface could emphasize or diminish the perceived 3D geometrical structures of a shape. The experimental results are in line with the simulated outputs reported in previous work. Our findings might introduce a new approach towards having more control over 3D appearance reproduction without changing the material or printer settings.
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| 8. |
- Bäcklund, Christian, et al.
(author)
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Exploring the relationship between personality and gaming disorder symptoms in a sample of Dota 2 players
- 2024
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In: Current Psychology. - : Springer. - 1046-1310 .- 1936-4733.
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Journal article (peer-reviewed)abstract
- This study explored the relationship between the big five personality traits and gaming disorder symptoms (GDS) in a sample of Dota 2 players. Recent research has indicated that the relationship between personality traits and GDS may depend on the video game genre investigated. However, the association between GDS and personality has yet to be investigated within a specific game, which may be even more relevant to explore as each game offers unique gameplay mechanics that can influence player behavior differently. Thus, the present study investigated the relationship between the big five personality traits and GDS in a sample of video game players from a specific game, DOTA 2 (n = 321, M = 23.25 years, SD = 4.51). Multiple linear regression was used to analyze GDS formatted as a composite score, and multinomial logistic regressions were further conducted for analyses in which gamers were classified into normal gamers (i.e., less than three criteria endorsed), moderate-risk gamers (i.e., four criteria endorsed), and high-risk gamers (i.e., all criteria endorsed). The analysis of the composite score showed a significant relationship between neuroticism, conscientiousness, agreeableness, and GDS. Analyses of the gaming classifications revealed that neuroticism was the most crucial factor concerning differentiating moderate-risk and high-risk from normal gamers. The findings and their practical implications are further discussed.
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| 9. |
- Hulaj, Rame, et al.
(author)
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A Motivational Model Explaining Performance in Video Games
- 2020
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In: Frontiers in Psychology. - : Frontiers Media S.A.. - 1664-1078. ; 11
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Journal article (peer-reviewed)abstract
- Esports are a rapidly growing phenomenon and understanding of factors underlying game performance are therefore of great interest. The present study investigated the influence of satisfaction of basic psychological needs (competence, autonomy, and relatedness), type of motivation (amotivation, external regulation, introjected regulation, identified regulation, integrated regulation, and intrinsic motivation), and number of matches played (time on task) on individuals’ performance on a matchmaking rating (MMR) in the video game Defence of the Ancients 2 (Dota 2). Collected data from 315 participants was included in the analyses. A web-based questionnaire was used to collect data and structural equation modelling (SEM) was performed to analyze the data. The results show that perceived competence and autonomy were the only significant predictors of MMR performance beyond matches played. Fulfillment of relatedness, as well as motivational factors, were not found to be predictors of MMR scores. The strong effect of matches played, used as proxy of time on task, emphasize the effect of time and practice as a critical aspect of video-game expertise.
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| 10. |
- Pranovich, Alina, 1993-, et al.
(author)
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Angular dependent reflectance spectroscopy of RGBW pigments
- 2022
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Conference paper (other academic/artistic)abstract
- 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.
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| 11. |
- Pranovich, Alina, 1993-, et al.
(author)
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Dot Off Dot Screen Printing with RGBW Reflective Inks
- 2023
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In: Journal of Imaging Science and Technology. - : The Society for Imaging Science and Technology. - 1062-3701 .- 1943-3522. ; 67:3
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Journal article (peer-reviewed)abstract
- Recent advances in pigment production resulted in the possibility to print with RGBW primaries instead of CMYK and performing additive color mixing in printing. The RGBW pigments studied in this work have the properties of structural colors, as the primary colors are a result of interference in a thin film coating of mica pigments. In this work, we investigate the angle-dependent gamut of RGBW primaries. We have elucidated optimal angles of illumination and observation for each primary ink and found the optimal angle of observation under diffuse illumination. We investigated dot off dot halftoned screen printing with RGBW inks on black paper and in terms of angle-dependent dot gain. Based on our observations, optimal viewing condition for the given RGBW inks is in a direction of around 30◦ to the surface normal. Here, the appearance of the resulting halftoned prints can be estimated well by Neugebauer formula (weighted averaging of the individual reflected spectra). Despite the negative physical dot gain during the dot off dot printing, we observe angularly dependent positive optical dot gain for halftoned prints. Application of interference RGBW pigments in 2.5D and 3D printing is not fully explored due to the technological limitations. In this work, we provide colorimetric data for efficient application of the angle-dependent properties of such pigments in practical applications.
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| 12. |
- Pranovich, Alina, 1993-, et al.
(author)
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Empirical BRDF model for goniochromatic materials and soft proofing with reflective inks.
- 2024
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In: IEEE Computer Graphics and Applications. - 0272-1716 .- 1558-1756.
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Journal article (peer-reviewed)abstract
- The commonly used analytic bidirectional reflectance distribution functions (BRDFs) do not model goniochromatism, that is, angle-dependent material color. The material color is usually defined by a diffuse reflectance spectrum or RGB vector and a specular part based on a spectral complex index of refraction. Extension of the commonly used BRDFs based on wave theory can help model goniochromatism, but this comes at the cost of significant added model complexity. We measured the goniochromatism of structual color pigments used for additive color printing and found that we can fit the observed spectral angular dependence of the bidirectional reflectance using a simple modification of the standard microfacet BRDF model. All we need to describe the goniochromatism is an empirically-based spectral parameter, which we use in our model together with a specular reflectance spectrum instead of the spectral complex index of refraction. We demonstrate the ability of our model to fit the measured reflectance of red, green, and blue commercial structural color pigments. Our BRDF model enables straightforward implementation of a shader for interactive preview of 3D objects with printed spatially and angularly varying texture.
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| 13. |
- Pranovich, Alina, 1993-
(author)
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Modelling appearance printing : Acquisition and digital reproduction of translucent and goniochromatic materials
- 2024
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 14. |
- Pranovich, Alina, 1993-, et al.
(author)
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Optical properties and appearance of fused deposition modelling filaments
- 2021
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In: Advances in Printing and Media Technology - Printing in the Digital Era : Proceedings of the 47<sup>th</sup> International Research Conference of iarigai. - : International Association of Research Organizations for the Information, Media and Graphic Arts Industries. - 9783948039028 ; , s. 134-140
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Conference paper (peer-reviewed)abstract
- The appearance of 3D-printed objects is affected by numerous parameters. Specifically, the colour of each point on the surface is affected not only by the applied material, but also by the neighbouring segments as well as by the structure underneath it. Translucency of the 3D printing inks is the key property needed for reproduction of surfaces resembling natural materials. However, the prediction of colour appearance of translucent materials within the print is a complex task that is of great interest. In this work, a method is proposed for studying the appearance of translucent 3D materials in terms of the surface colour. It is shown how the thickness of the printed flat samples as well as the background underneath affect the colour. By studying diffuse reflectance and transmittance of layers of different thicknesses, apparent, spectral optical properties were obtained, i.e., extinction and scattering coefficients, in the case of commercially available polylactic acid (PLA) filaments for Fused Deposition Modelling (FDM) printers. The coefficients were obtained by fitting a simplistic model to the measured diffuse reflectance as a function of layer thickness. The results were verified by reconstructing reflected spectra with the obtained parameters and comparing the estimated colour to spectrophotometer measurements. The resulting colour differences in terms of the CIEDE2000 standard are all below 2.
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| 15. |
- Pranovich, Alina, 1993-, et al.
(author)
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Surface Discretisation Effects on 3D Printed Surface Appearance
- 2020
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In: CEUR-WS.org.
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Conference paper (peer-reviewed)abstract
- The spatial resolution of 3D printing is finite. The necessary discretisation of an object before printing produces a step-like surface structure that influences the appearance of the printed objects. To study the effect of this discretisation on specular reflections, we print surfaces at various oblique angles. This enables us to observe the step-like struc- ture and its influence on reflected light. Based on the step-like surface structure, we develop a reflectance model describing the redistribution of the light scattered by the surface, and we study dispersion effects due to the wavelength dependency of the refractive index of the material. We include preliminary verification by comparing model predictions to photographs for different angles of observation.
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