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| 4. |
- Abedini, Fereshteh, 1989-
(författare)
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2D and 3D Halftoning for Appearance Reproduction
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
(författare)
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3D Halftoning based on Iterative Method Controlling Dot Placement
- 2020
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Konferensbidrag (refereegranskat)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.
(författare)
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Structure-Aware Halftoning Using the Iterative Method Controlling the Dot Placement
- 2021
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Ingår i: Journal of Imaging Science and Technology. - : I S & T-SOC IMAGING SCIENCE TECHNOLOGY. - 1062-3701 .- 1943-3522. ; 65:6
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Tidskriftsartikel (refereegranskat)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.
(författare)
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The Effect of Halftoning on the Appearance of 3D Printed Surfaces
- 2021
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Konferensbidrag (refereegranskat)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.
(författare)
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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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Ingår i: Current Psychology. - : Springer. - 1046-1310 .- 1936-4733.
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Tidskriftsartikel (refereegranskat)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. |
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| 10. |
- Hulaj, Rame, et al.
(författare)
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A Motivational Model Explaining Performance in Video Games
- 2020
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Ingår i: Frontiers in Psychology. - : Frontiers Media S.A.. - 1664-1078. ; 11
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Norberg, Ole, 1970-, et al.
(författare)
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Extending color primary set in spectral vector error diffusion by multilevel halftoning
- 2013
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Ingår i: Color Imaging XVIII. - Bellingham : SPIE - International Society for Optical Engineering. - 9780819494252 ; , s. 8652OM-1-8652OM-9
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Konferensbidrag (refereegranskat)abstract
- Ever since its origin in the late 19th century, a color reproduction technology has relied on a trichromatic color reproduction approach. This has been a very successful method and also fundamental for the development of color reproduction devices. Trichromatic color reproduction is sufficient to approximate the range of colors perceived by the human visual system. However, tricromatic systems only have the ability to match colors when the viewing illumination for the reproduction matches that of the original. Furthermore, the advancement of digital printing technology has introduced printing systems with additional color channels. These additional color channels are used to extend the tonal range capabilities in light and dark regions and to increase color gamut. By an alternative approach the addition color channels can also be used to reproduce the spectral information of the original color. A reproduced spectral match will always correspond to original independent of lighting situation. On the other hand, spectral color reproductions also introduce a more complex color processing by spectral color transfer functions and spectral gamut mapping algorithms. In that perspective, spectral vector error diffusion (sVED) look like a tempting approach with a simple workflow where the inverse color transfer function and halftoning is performed simultaneously in one single operation. Essential for the sVED method are the available color primaries, created by mixing process colors. Increased numbers of as well as optimal spectral characteristics of color primaries are expected to significantly improve the color accuracy of the spectral reproduction. In this study, sVED in combination with multilevel halftoning has been applied on a ten channel inkjet system. The print resolution has been reduced and the underlying physical high resolution of the printer has been used to mix additional primaries. With ten ink channels and halfton cells built-up by 2x2 micro dots where each micro dot can be a combination of all ten inks the number of possible ink combinations gets huge. Therefore, the initial study has been focused on including lighter colors to the intrinsic primary set. Results from this study shows that by this approach the color reproduction accuracy increases significantly. The RMS spectral difference to target color for multilevel halftoning is less than 1/6 of the difference achieved by binary halftoning. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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| 12. |
- Norberg, Ole, 1970-, et al.
(författare)
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Spectral Vector Error Diffusion - Promising Road or Dead End?
- 2012
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Ingår i: Twentieth Color and Imaging Conference. - Springfield. VA, USA : The Society for Imaging Science and Technology. - 9780892083039 ; , s. 329-334
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Konferensbidrag (refereegranskat)abstract
- The interest for spectral color reproduction has increased with the growing field of multispectral imaging and the increasing use of multi-colorant printing systems. Spectral color reproduction, i.e. aiming at reproducing the spectral reflectance of an original, first requires a colorant separation for a multi-colorant printing system, followed by halftoning of each the color channels. Spectral vector error diffusion, sVED, has previously been introduced as a tempting alternative for spectral color reproduction, since the method combines the colorant separation and the halftoning in a single step. Only the spectral properties of the Neugebauer primaries are needed as input, and there is no need to invert a complex printer model for the colorant separation. Previously, spectral vector error diffusion has been positively evaluated for simulated prints, assuming a perfect printer and no dot gain. In this study, we evaluate the performance of sVED in practice, for real prints.Spectral vector error diffusion has been used to reproduce 1000 spectral targets, all within the spectral gamut of the printing system. The resulting color patches have been printed in various print resolutions, using a 10-colorant inkjet printing system. The experimental results reveal a remarkably large difference between the reproduction errors for the printed samples compared to the simulated spectra from the digital halftones. The results show a strong relation between the print resolution and the magnitude of the reproduction error, with lower resolutions giving smaller errors, due to the effect of dot gain in the printing process. The experimental results imply that in its current form, without compensation for physical and optical dot gain, spectral vector error diffusion produces unacceptable spectral and colorimetric reproduction errors, for any print resolutions used in practice.The results further show that the sVED method in many cases produces color patches that appear noisy and visually unpleasant. By replacing the spectral RMS difference with the ΔE94 color difference as criterion in the sVED algorithm, the graininess as well as the resulting color difference was decreased. However, the improvements in colorimetric performance and more visually pleasant reproductions, comes at the cost of an increase in spectral reproduction errors.
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| 13. |
- Nyström, Daniel, 1974-
(författare)
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A Close-Up Investigation of Halftone Color Prints
- 2008
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Ingår i: TAGA 2008 proceedings. - Sewickley, PA, USA : TAGA - Technical Association of the Graphic Arts. - 9781935185000 ; , s. 347-363
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modeling the color reproduction of halftone prints is difficult, because of light scattering, causing optical dot gain. Most available models are limited to macroscopic color measurements, averaging the reflectance over an area that is large relative the dot size. The aim of this study is to go beyond the macroscopic approach and study optical dot gain on a micro-scale level, using colorimetric images of printed halftones. An experimental imaging system, combining the accuracy of color measurement instruments with a high spatial resolution, opens up possibilities to better study the color reproduction in halftone color prints. The main focus is to study how the reflectance values of the printed dots and the paper between the dots, Ri(Fi) and Rp(Fi), vary with the dot area fraction. Micro-scale images, i.e. when the resolution of the images is high in relation to the resolution of the halftone, allow for measurements of the individual halftone dots, as well as the paper between them. To capture the characteristics of large populations of halftone dots, histograms are computed. From the histogram data it is possible to derive the mean reflectance, R, the reflectance for the dots, Ri(Fi), and the paper between the dots, Rp(Fi). The true dot area coverage, including the physical dot gain, is computed using histogram data, as well as using line scans in the micro-scale images. A previously proposed extension of the Murray-Davies equation, incorporating Ri(Fi) and Rp(Fi), is evaluated. The model is further extended to handle color prints, predicting tristimulus values, by using 3D histograms in CIEXYZ color space. To reduce the complexity, projection from XYZ coordinates into one dimensional color distributions are used. The prediction errors of the model were found to be equivalent, or better, to that of the Yule-Nielsen model using an optimal n-factor. However, unlike Yule-Nielsen, the extended Murray-Davies model preserves the linear additivity of reflectance, thus providing a better physical description of optical dot gain in halftone color prints.
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| 15. |
- Nyström, Daniel, 1974-
(författare)
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A Micro-Scale View on Color Reproduction
- 2008
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Ingår i: CGIV 2008/MCS'08 4th European Conference on Colour in Graphics, Imaging, and Vision and 10th International Symposium on Multispectral Colour Science. - Springfield, VA, USA : The Society for Imaging Science and Technology. ; , s. 542-
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Konferensbidrag (refereegranskat)abstract
- Modeling color print reproduction is difficult, mainly because of light scattering, causing optical dot gain. Most available models are based on macroscopic color measurements, the average value over an area that is large relative to the halftone dot size. The aim of this study is to go beyond the macroscopic approach, to study color print reproduction on a micro-scale level. An experimental imaging system, combining the accuracy of color measurement instruments with a high spatial resolution, opens up new possibilities to study and model color print reproduction. The main focus is to study how the reflectance values of the printed dots and the paper between them vary with the dot area fraction. A previously proposed expansion of the Murray-Davies model is further developed to handle color prints, predicting tristimulus values. The color of the halftone dots and the paper between them is derived from 3D color histograms in CIEXYZ color space. The prediction errors of the model were found to be equivalent, or better, to that of the Yule-Nielsen model using an optimal n-factor. However, unlike Yule-Nielsen, the expanded Murray-Davies model takes into account the varying reflectance of the ink and paper, and preserves the linear additivity of reflectance, thus providing a better physical description of optical dot gain in color reproduction.
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| 16. |
- Nyström, Daniel, 1974-, et al.
(författare)
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Addressing the colorimetric redundancy in 11-ink color separation
- 2017
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Ingår i: Color Imaging XXII: Displaying, Processing, Hardcopy, and Applications. - : The Society for Imaging Science and Technology. ; , s. 184-189
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Konferensbidrag (refereegranskat)abstract
- To improve color reproduction, many printers today use extra colorants, in addition to the traditional four inks (Cyan, Magenta, Yellow and Black). Adding the complementary colorants (Red, Green and Blue) increases the gamut of reproducible colors, while lighter versions of the primary inks can be added to reduce graininess and dot visibility. Using more than three inks introduces colorimetric redundancy in the color separation process, because different ink combinations can reproduce the same target color. When additional inks are introduced, this redundancy rapidly increases, and it is thus crucial to introduce additional constraints in the color separation process, to improve determinacy and to optimize different aspects of print quality. This study focuses on an analysis of the redundancy in the color separation process for an 11-ink printer. It is investigated how the extensive colorimetric redundancy can be utilized to select optimal ink combinations to meet the, sometimes contradictory, criteria of color accuracy, graininess and ink consumption. Analysis of the results of applying different criteria in the color separation process shows that the result heavily depends on the selected criterion. For example, prioritizing graininess will improve print quality by reducing dot visibility, imposing the use of lighter inks, but it will also increase ink consumption.
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| 17. |
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| 18. |
- Nyström, Daniel, 1974-
(författare)
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Colorimetric and Multispectral Image Acquisition
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The trichromatic principle of representing color has for a long time been dominating in color imaging. The reason is the trichromatic nature of human color vision, but as the characteristics of typical color imaging devices are different from those of human eyes, there is a need to go beyond the trichromatic approach. The interest for multi-channel imaging, i.e. increasing the number of color channels, has made it an active research topic with a substantial potential of application.To achieve consistent color imaging, one needs to map the imaging-device data to the device-independent colorimetric representations CIEXYZ or CIELAB, the key concept of color management. As the color coordinates depend not only on the reflective spectrum of the object but also on the spectral properties of the illuminant, the colorimetric representation suffers from metamerism, i.e. objects of the same color under a specific illumination may appear different when they are illuminated by other light sources. Furthermore, when the sensitivities of the imaging device differ from the CIE color matching functions, two spectra that appear different for human observers may result in identical device response. On contrary, in multispectral imaging, color is represented by the object’s physical characteristics namely the spectrum which is illuminant independent. With multispectral imaging, different spectra are readily distinguishable, no matter they are metameric or not. The spectrum can then be transformed to any color space and be rendered under any illumination.The focus of the thesis is high quality image-acquisition in colorimetric and multispectral formats. The image acquisition system used is an experimental system with great flexibility in illumination and image acquisition setup. Besides the conventional trichromatic RGB filters, the system also provides the possibility of acquiring multi-channel images, using 7 narrowband filters. A thorough calibration and characterization of all the components involved in the image acquisition system is carried out. The spectral sensitivity of the CCD camera, which can not be derived by direct measurements, is estimated using least squares regression, optimizing the camera response to measured spectral reflectance of carefully selected color samples.To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based approach, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical approach, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression.The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. Because of the media-dependency, the characterization functions should be derived for each combination of media and colorants. However, accurate spectral data reconstruction requires for multi-channel imaging, using the model-based approach. Moreover, the model-based approach is general, since it is based on the spectral characteristics of the image acquisition system, rather than the characteristics of a set of color samples.
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| 19. |
- Nyström, Daniel, 1974-
(författare)
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Colorimetric and Multispectral Image Acquisition Using Model-based and Empirical Device Characterization
- 2007
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Ingår i: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 798-807
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Konferensbidrag (refereegranskat)abstract
- The focus of the study is high quality image acquisition in colorimetric and multispectral formats. The aim is to combine the spatial resolution of digital images with the spectral resolution of color measurement instruments, to allow for accurate colorimetric and spectral measurements in each pixel of the acquired images. An experimental image acquisition system is used, which besides trichromatic RGB filters also provides the possibility of acquiring multi-channel images, using a set of narrowband filters. To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based characterization, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical characterization, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression. The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. However, accurate spectral reconstructions requires for multi-channel imaging, with the best results obtained using the model-based approach.
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| 20. |
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| 21. |
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| 22. |
- Nyström, Daniel, 1974-
(författare)
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High Resolution Analysis of Halftone Prints : A Colorimetric and Multispectral Study
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To reproduce color images in print, the continuous tone image is first transformed into a binary halftone image, producing various colors by discrete dots with varying area coverage. In halftone prints on paper, physical and optical dot gains generally occur, making the print look darker than expected, and making the modeling of halftone color reproduction a challenge. Most available models are based on macroscopic color measurements, averaging the reflectance over an area that is large in relation to the halftone dots. The aim of this study is to go beyond the macroscopic approach, and study halftone color reproduction on a micro-scale level, using high resolution images of halftone prints. An experimental imaging system, combining the accuracy of color measurement instruments with a high spatial resolution, opens up new possibilities to study and analyze halftone color prints.The experimental image acquisition offers a great flexibility in the image acquisition setup. Besides trichromatic RGB filters, the system is also equipped with a set of 7 narrowband filters, for multi-channel images. A thorough calibration and characterization of all the components in the imaging system is described. The spectral sensitivity of the CCD camera, which can not be derived by direct measurements, is estimated using least squares regression. To reconstruct spectral reflectance and colorimetric values from the device response, two conceptually different approaches are used. In the model-based characterization, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical characterization, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression techniques.Micro-scale images, referring to images whose resolution is high in relation to the resolution of the halftone, allow for measurements of the individual halftone dots, as well as the paper between them. To capture the characteristics of large populations of halftone dots, reflectance histograms are computed as well as 3D histograms in CIEXYZ color space. The micro-scale measurements reveal that the reflectance for the halftone dots, as well as the paper between the dots, is not constant, but varies with the dot area coverage. By incorporating the varying micro-reflectance in an expanded Murray-Davies model, the nonlinearity caused by optical dot gain can be accounted for without applying the nonphysical exponentiation of the reflectance values, as in the commonly used Yule-Nielsen model.Due to their different intrinsic nature, physical and optical dot gains need to be treated separately when modeling the outcome of halftone prints. However, in measurements of reflection colors, physical and optical dot gains always co-exist, making the separation a difficult task. Different methods to separate the physical and optical dot gain are evaluated, using spectral reflectance measurements, transmission scans and micro-scale images. Further, the relation between the physical dot gain and the halftone dot size is investigated, demonstrated with FM halftones of various print resolutions. The physical dot gain exhibits a clear correlation with the dot size and the dot gain increase is proportional to the increase in print resolution. The experimental observations are followed by discussions and a theoretical explanation.
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| 23. |
- Nyström, Daniel, 1974-, et al.
(författare)
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High resolution properties of color prints
- 2005
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Ingår i: Bijing International Conference on Imaging,2005. - Beijing, China : Science Press. ; , s. 242-243
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 24. |
- Nyström, Daniel, 1974-, et al.
(författare)
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Improved Spectral Vector Error Diffusion by Dot Gain Compensation
- 2013
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Ingår i: Color Imaging XVIII. - Bellingham : SPIE - International Society for Optical Engineering. - 9780819494252 ; , s. 8652OL-1-8652OL-11
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Konferensbidrag (refereegranskat)abstract
- Abstract: Spectral Vector Error Diffusion, sVED, is an interesting approach to achieve spectral color reproduction, i.e. reproducing the spectral reflectance of an original, creating a reproduction that will match under any illumination. For each pixel in the spectral image, the colorant combination producing the spectrum closest to the target spectrum is selected, and the spectral error is diffused to surrounding pixels using an error distribution filter. However, since the colorant separation and halftoning is performed in a single step in sVED, compensation for dot gain cannot be made for each color channel independently, as in a conventional workflow where the colorant separation and halftoning is performed sequentially. In this study, we modify the sVED routine to compensate for the dot gain, applying the Yule-Nielsen n-factor to modify the target spectra, i.e. performing the computations in (1/n)-space. A global n-factor, optimal for each print resolution, reduces the spectral reproduction errors by approximately a factor of 4, while an n-factor that is individually optimized for each target spectrum reduces the spectral reproduction error to 7% of that for the unmodified prints. However, the improvements when using global n-values are still not sufficient for the method to be of any real use in practice, and to individually optimize the n-values for each target is not feasible in a real workflow. The results illustrate the necessity to properly account for the dot gain in the printing process, and that further developments is needed in order to make Spectral Vector Error Diffusion a realistic alternative for spectral color reproduction.
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| 25. |
- Nyström, Daniel, 1974-
(författare)
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Micro-reflectance Measurements of Multiple Colorants in Halftone Prints
- 2011
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Ingår i: TAGA (Technical Association of the Graphic Arts) 2011. - Sewickley, PA, USA : TAGA - Technical Association of the Graphic Arts. - 9781935185031 ; , s. 157-176
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modeling color reproduction in halftone prints is difficult, mainly because of light scattering in the substrate, causing optical dot gain. Most available models are limited to macroscopic color measurements, averaging the reflectance over an area that is large relative the halftone dot size. The reflectance values for the full tone ink and the unprinted paper are used as input, and these values are assumed to be constant. An experimental imaging system, combining the accuracy of color measurement instruments with a high spatial resolution, allows us to measure the individual halftone dots, as well as the paper between them. Microscopic reflectance measurements reveal that the micro-reflectance of the printed dots and the paper between them is not constant, but varies with the dot area coverage. By incorporating the varying micro-reflectance values of the ink and paper in an expanded Murray-Davies model, we have previously shown that the resulting prediction errors are smaller than for the famous Yule-Nielsen model. Moreover, unlike Yule-Nielsen, the expanded Murray-Davies model takes into account the varying micro-reflectance for the printed dots and the paper, thus providing a better physical description of optical dot gain in halftone reproduction.In this study, we further extend the methodology to handle color prints, predicting tristimulus values for prints with multiple and overlapping colorants. After converting the microscopic images of halftone prints into CIEXYZ color space, 3D histograms are computed. In the 3D histograms, the paper and the inks appear as clusters, with the transitions between the clusters corresponding to the edges of halftone dots. The tristimulus values for the paper and the different combinations of ink are computed as the centers of gravity for the clusters in the 3D histogram. From the microscopic images we can also compute the physical dot area coverage for each of the Neugebauer primaries, which typically differ from the nominal one, due to physical dot gain. The result is an expanded Neugebauer model, employing the varying tristimulus values of the paper and primary inks, as well as for overlapping, secondary colors. Experimental results confirm the accuracy of the proposed methodology, whencompared to measurements using a spectrophotometer. Further, the results have shown that the variation of the micro-reflectance of the Neugebauer primaries is large, and depends strongly on the total dot area coverage.
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| 26. |
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| 27. |
- Nyström, Daniel, 1974-
(författare)
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Microscopic Color Measurement of Halftone Prints
- 2010
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Ingår i: NIP26: The 26th International Conference on Digital Printing Technologies. - Sprinfield, VA, USA : The Society for Imaging Science and Technology. - 9780892082926 ; , s. 459-462
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modeling halftone print reproduction is difficult, mainlybecause of light scattering, causing optical dot gain. Mostavailable models are based on macroscopic color measurements,integrating the reflectance over an area that is large relative thehalftone dot size. The reflectance values for the full tone and theunprinted paper are used as input, and these values are assumedto be constant. An experimental imaging system, combining theaccuracy of color measurement instruments with a high spatialresolution, allows us to measure the individual halftone dots, aswell as the paper between them. Microscopic color measurementsreveal that the micro-reflectance of the printed dots and the paperis not constant, but varies with the dot area fraction. Byincorporating the varying reflectance of the ink and paper in anexpanded Murray-Davies model, the resulting prediction errorsare smaller than for the Yule-Nielsen model. However, unlikeYule-Nielsen, the expanded Murray-Davies model preserves thelinear additivity of reflectance, thus providing a better physicaldescription of optical dot gain. The microscopic colormeasurements further show that the color shift of the ink andpaper depends on the halftone geometry and the print resolution.In this study, we measure and characterize the varying microreflectanceof ink and paper with respect to properties of thehalftones, using AM and FM prints of various print resolutions.
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| 28. |
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| 29. |
- Nyström, Daniel, 1974-
(författare)
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Reconstructing Spectral and Colorimetric Data Using Trichromatic and Multi-channel Imaging
- 2007
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Ingår i: 9th International Symposium on Multispectral Color Science and Application. - Springfield, VA, USA : The Society for Imaging Science and Technology. - 9780892082728 ; , s. 45-52
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Konferensbidrag (refereegranskat)abstract
- The aim of the study is to reconstruct spectral and colorimetric data, using trichromatic and multi-channel imaging. An experimental image acquisition system is used, which besides trichromatic RGB filters also provides the possibility of acquiring multi-channel images, using 7 narrowband filters. To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based approach, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. A priori knowledge on the smooth nature of spectral reflectances is utilized, by representing the reconstructed spectra as linear combinations of basis functions, using Fourier basis and a database of real reflectance spectra. In the empirical approach, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of training colors to the corresponding colorimetric and spectral measurements. Beside colorimetric regression, mapping device values directly to CIEXYZ and CIELAB, experiments are also made on reconstructing spectral reflectance, using least squares regression techniques.The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. Because of the media-dependency, the characterization functions must be derived for each combination of media and colorants. However, accurate spectral reconstructions require for multi-channel imaging, using model-based device characterization. Moreover, the model-based approach is general, since it is based on the spectral characteristics of the image acquisition system, rather than the characteristics of a set of color samples.
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| 30. |
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| 31. |
- Nyström, Markus, 1973-, et al.
(författare)
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To what extent is subjective well-being in late adulthood related to subjective and objective memory functioning? : Five-year cross-lagged panel analyses
- 2019
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Ingår i: Aging & Mental Health. - : Taylor & Francis. - 1360-7863 .- 1364-6915. ; 23:1, s. 92-99
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Tidskriftsartikel (refereegranskat)abstract
- Background: Population aging motivated a focus in contemporary research on factors, e.g. cognitive functioning, that contribute to ‘aging well.’ However, something that has been overlooked is relation between memory functioning, determined by objective tests as well as subjective memory ratings, and subjective well-being (SWB).Objectives: The aim of the present study was to investigate cross-sectional and longitudinal (cross-lagged) relationships between episodic memory (both subjective and objective) and SWB.Method: A total of 586 older individuals (60–90 years) were assessed on multiple measures of the targeted constructs at baseline (Time 1) as part of the Betula cohort study. Five years later (Time 2), 354 of the participants returned for follow-up measurements and were included in cross-lagged panel analyses.Results: As expected, objective memory and subjective memory showed a pattern of cross-sectional age deficits and a mean level longitudinal decline was observed for objective memory. By contrast, SWB showed stable mean levels both across age and time. No cross-sectional or cross-lagged associations were observed between SWB and objective memory, whereas subjective memory and SWB showed a cross-sectional association.Conclusion: The results underscore that successful aging is a multifaceted construct with no or only weak associations between the investigated components. However, SWB and rate of change at the individual level should be considered to define successful aging.
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| 32. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Angular dependent reflectance spectroscopy of RGBW pigments
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 33. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Dot Off Dot Screen Printing with RGBW Reflective Inks
- 2023
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Ingår i: Journal of Imaging Science and Technology. - : The Society for Imaging Science and Technology. - 1062-3701 .- 1943-3522. ; 67:3
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Tidskriftsartikel (refereegranskat)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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| 34. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Empirical BRDF model for goniochromatic materials and soft proofing with reflective inks.
- 2024
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Ingår i: IEEE Computer Graphics and Applications. - 0272-1716 .- 1558-1756.
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Tidskriftsartikel (refereegranskat)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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| 35. |
- Pranovich, Alina, 1993-
(författare)
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Modelling appearance printing : Acquisition and digital reproduction of translucent and goniochromatic materials
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 36. |
- Pranovich, Alina, 1993-, et al.
(författare)
-
Optical properties and appearance of fused deposition modelling filaments
- 2021
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Ingår i: 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
-
Konferensbidrag (refereegranskat)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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| 37. |
- Pranovich, Alina, 1993-, et al.
(författare)
-
Surface Discretisation Effects on 3D Printed Surface Appearance
- 2020
-
Ingår i: CEUR-WS.org.
-
Konferensbidrag (refereegranskat)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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