How can one create an aura from a digital reproduction? According to researchers like Walter Benjamin (1936) this is not possible. However with todays technology and digitalmedia it is worth looking into how it would be possible.Museums are looking for ways to expand the experiences of their exhibitions with thehelp of digital media, but research into authenticity and aura in digital reproductions islimited. This research aims to answer if it is possible to create an aura from a digitalreproduction and in what way that would be done.

Amongst its innumerable effects on society, the proliferation of digital media has transformed the institution of art, with new forms and channels of digital content delivery allowing unprecedented levels of reproducibility. This reproducibility has allowed artworks and artifacts to be copied, shared, and experienced in a multitude of new ways, often far beyond the original artist’s intentions or expectations.  Contemporary technologies such as advanced 3D object rendering, photogrammetry and Virtual Reality have established a new era of reproduction beyond simplistic image replication. This new era has not only revolutionised the artwork itself, but also the relationship between the viewers of art and the original piece, or the aura. The power of reproduction through digital media has even allowed the complete simulation of traditional spaces for art themselves, as seen in the growth of entirely digital museums and digital art galleries.  As an ever-increasing number of museums are joining the trend of digitising and releasing objects in their collections online, and with existing literature mainly focused on 2D image-based reproduction, but not the affordances brought by photogrammetry and 3D replication technology, this study will explore how the new possibilities inherent to these technologies challenge prior research on digital aura within art galleries.  By contributing to the body of Walter Benjamin scholarship, and building from previous research by Ding (2017), this thesis is centred around exploring a case study of a group of Swedish museums who have begun digitising artifacts in their collection through photogrammetry and freely releasing them to the public online.

The digital reproduction of materials has developed greatly over the past decades. The improved interactive rendering technology available nowadays enables broad digital visualization applications like gaming, cinema and film production, advertising, and online shopping. These recent advances in digital technologies are also playing an important role in the improvement of some industrial processes such as computer-aided design and manufacturing, virtual prototyping, and scientific visualization and simulation. Currently, many rendering software packages provide impressive images and often even claim photorealism. However, producing realistic appearance images is very challenging taking into account the high sensitivity of the human visual system. The visual appearance of products is still an important aspect to take into account even for the digital simulation of materials, since the appearance of these simulated products on the screen is still a critical parameter in the purchase decision of customers. During the last years different efforts have been carried out by industrial manufacturers in different applications, such as textile, cosmetic, automotive, etc., to provide attractive visual effects and new visual impressions of their products using, for instance, innovative effect pigments, also called goniochromatic pigments. The digital rendering of these pigments is a very active hot topic since this type of coatings changes considerably its visual attributes such as color and texture with the illumination/viewing geometry. Achieving accurate simulation of these materials demands an extra effort due to the physical complexity of their surfaces. Special BRDFs (bidirectional reflectance distribution functions) reflectance models are needed to characterize their visual appearance. This complex appearance is produced due to the presence of special effect pigments containing metallic, interference, or pearlescent pigments, which are responsible for the strong dependence of the color of these coatings on viewing and illumination directions. These pigments also exhibit visually complex texture effects such as sparkle and graininess. Under bright direct illumination conditions, such as sunlight, the flakes create a sparkling effect, while under diffuse illumination such as a cloudy sky, effect coatings create a salt and pepper appearance or a light/dark irregular pattern, which is usually referred to as graininess or coarseness. Two main issues limit the digital reproduction of effect pigments. The first issue is related to the current display technologies. The quality of the displays is an essential component toward accurate color reproduction of materials. Previous studies have evaluated the validity of available display technologies for the visualization and digital reproduction of effect pigments, which are usually not enough for the reproduction of such a wide variety of colors due to their limited color gamut. The second limitation is more related to the current rendering software. The color accuracy of their images is often not sufficient for the reproduction of colors and effects produced by these materials. The available rendering software provides impressive images that serve the needs for applications such as the cinema and games industries, but when it comes to more critical applications such as automotive design, the color accuracy of their rendered images is not accurate enough, especially for such complex materials such as effect pigments. The first issue is addressed in this thesis by, evaluating the performance of the new Quantum dots (QDs) display technology for the reproduction of effect pigments. For further improving the display capability, a new solution is given by developing a multi-primary display model based on the QDs technology (addressed in the first research article of this thesis in chapter 1). The proposed multi-primary display model provides an expanded color gamut, which guarantees a better reproduction of effect pigments. In a first step, the emission spectral radiance curves of the three RGB channels of a commercial QD display were fitted to a four-parameter function. From this modeling, it is possible to gain new theoretical color primaries by selecting new spectral peaks (cyan, yellow, magenta, and/or additional RGB primaries) and imposing colorimetric conditions for the resulting white of this proposed theoretical multi-primary display. Proper characterization to assess the performance of the display was conducted to know if the basic “gain-offset-gamma” (GOG) model can be used for direct and inverse color reproduction (from RGB to CIE-XYZ, and vice versa). The GOG model was found to well characterize this display. The spatial uniformity of the display was also evaluated in luminance and color chromaticity terms. Finally, with the primaries modeling and color characterization based on the GOG model, a 5-primary model (RGBYC) was tested. The evaluation of this theoretical RGBYC display model confirms the gamut enlargement, which can also improve goniochromatic color reproduction. In the second place, and focusing on the second issue, a big portion of the work of this thesis was dedicated to the development of a new 3D rendering tool for improved and accurate visualization of the complete appearance of effect coatings, including metallic effects, sparkle, and iridescence (addressed in the second and third research articles of this thesis in chapters 2 and 3). This task was carried on by firstly building a specific rendering framework for this purpose, using a multi-spectral and physically based rendering approach, and secondly, by validating the performance of this rendering framework through psychophysical tests. Spectral reflectance measurements and sparkle indices from a commercially available multi-angle spectrophotometer (BYK-mac i) were used together with a physically based approach, such as flake-based reflectance models, to efficiently implement the appearance reproduction from a small number of bidirectional measurement geometries. With this rendering framework, a virtual representation of a set of effect coating samples is reproduced on an iPad display, by simulating how these samples would be viewed inside a Byko-spectra effect light booth. Therefore, for this purpose, an accurate virtual representation of the Byko light booth was built using a physically based representation of global illumination. The rendering framework also accounts for the colorimetric specifications of the rendering display (iPad5) by applying the recent device-specific MDCIM model. The appearance fidelity of the rendering was validated through psychophysical methods. For this task, observers were asked to evaluate the most important visual attributes that directly affect the appearance of effect coatings, i.e., color, the angular dependence of color (color flop), and visual texture (sparkle and graininess). Observers were asked to directly compare the rendered samples with the real samples inside the Byko-spectra effect light booth. The visual validation was performed in three different steps. In the first study, the accuracy of rendering the color of solid samples is evaluated. In a second step, the accuracy of rendering the color flop of effect coatings is validated by conducting two separate visual tests, by using flat and curved samples respectively. In the third and last step, the digital reproduction of both color and texture of metallic samples is tested, by including texture effects in the rendering by using a sparkle visualization model. The parameters of the sparkle visualization model were optimized based on sparkle measurement data from the BYK-mac i instrument using a matrix-adjustment model. Results from the visual evaluations prove the high color accuracy of the developed rendering tool. In the first test, the visual acceptability of the rendering was 80%. This percentage is much better than what was found in a previous investigation using the default sRGB color encoding space. Results of the second study show an improved accuracy when curved samples were used (acceptability of 93% vs 80%). The final visual test shows high visual acceptability of the rendering at 90%. In conclusion, this thesis provides a method for accurate digital simulation of effect coatings, by developing a multispectral and physically based rendering approach on a simple iPad tablet computer. The research developed in this thesis comes with many advances in the scientific and industrial levels, with a great contribution to the development of innovative tools for digitization of materials, as needed in today’s society. / This thesis was carried out under the financial assistance of the Spanish Ministry of Economy and Competitiveness through the pre-doctoral fellowship FPIBES-2016-077325, and the research projects DPI2015-65814-R and RTI2018-096000-B-I00.

Στη Διδακτορική Διατριβή αναλύονται ζητήματα που αφορούν την ασύρματη μετάδοση καθώς και την απευθείας εκπομπή ψηφιακών ηχητικών σημάτων με σκοπό την βελτιστοποίηση των τεχνικών αυτών. Ως προς τo σκέλος της ασύρματης μετάδοσης, η διατριβή εστιάστηκε σε δίκτυο WLAN με υποστήριξη QoS. Για την μελέτη του συστήματος διεξήχθησαν δοκιμές χρησιμοποιώντας πρωτότυπη πλατφόρμα που επιτρέπει την μετατροπή ηχητικών ροών για την εισαγωγή τους και εξαγωγή τους σε εφαρμογή εξομοίωσης δικτύου ώστε να αξιολογηθεί η πιστότητα ηχητικής αναπαραγωγής. Η ανάλυση του συστήματος οδήγησε στην ανάπτυξη πρωτότυπης τεχνικής για τον συγχρονισμό διακριτών καναλιών αναπαραγωγής, που μπορεί να εφαρμοστεί με χρήση τυπικού υλικού WLAN καθώς και πρωτότυπου αλγορίθμου για την συγκάλυψη ακουστών παραμορφώσεων που ενδεχομένως εισάγονται κατά τη μετάδοση. Επίσης, στη διατριβή εισάγονται αποτελέσματα με νέες μεθόδους που σχετίζονται με τη μελέτη Μοναδιαίων Συστοιχιών Ψηφιακής Εκπομπής που οδηγούνται από σήμα Σίγμα-Δέλτα ενός ψηφίου, όπως στο πρότυπο DSD. Η προσέγγιση βασίζεται σε πρωτότυπο αλγόριθμο αντιστοίχησης ροής ενός ψηφίου σε στοιχεία ακουστικής εκπομπής και παρουσιάζει σημαντικά πλεονεκτήματα, ως προς την επιτυγχανόμενη πιστότητα και κατευθυντικότητα, όσο και στην δυνατότητα υλοποίησης. Ο σχεδιασμός και η λειτουργία πρωτοτύπου ψηφιακού ηχείου Σίγμα-Δέλτα τεκμηριώνουν τη θεωρητική ανάλυση ενώ οι μετρήσεις που ελήφθησαν από την κατασκευή βρίσκονται σε αντιστοιχία με τις αναμενόμενες από αντίστοιχες εξομοιώσεις, αλλά διάφοροι πρακτικοί περιορισμοί οδηγούν σε ηχητική πιστότητα κατώτερη της αναμενόμενης. / The dissertation analyzes issues concerning the wireless transmission and the direct emission of digital audio signals, in order to optimize these techniques. Regarding the wireless transmission, the dissertation focuses on the WLAN family of networks, supporting QoS. In order to study the system, trials were conducted using a novel platform that allows the conversion of audio streams for them to be imported an exported from a network simulation application, facilitating the final audio playback fidelity estimation. The above analysis led to the development of a prototype technique for the synchronization of discreet reproduction channels that can be implemented using typical WLAN hardware, as well as a prototype algorithm for concealing audible distortion that might be added during the transmission. Moreover, results using new methods relating to the study of Unary Digital Transmission Arrays driven by one-bit Delta-Sigma signals, as in the DSD standard, are introduced in the dissertation. The approach is based on a prototype algorithm for mapping a one-bit stream to the acoustic transmission elements and exhibits important advantages, namely increased fidelity and improved directivity, as well as ease of implementation. The design and operation of the prototype digital Delta-Sigma speaker substantiates the theoretical analysis, while the measurements obtained from the device are in accordance with what expected from respective simulations. However, various practical limitations lead to lower than expected acoustic fidelity.

The digital copy is rapidly becoming the dominant form in which researchers encounter cultural heritage. In this situation, the relation between the original and the digital reproduction has become a crucial, yet too little discussed problem. This thesis investigates this relation through two questions: (1) Which is the ontological status of the reproduction in relation to the original, and (2) How is the original mediated to its digital format? Question (1) is answered in dialogue with previous research: The reproduction is a new artefact, but with a relation (of similiarity) to the original. It is the understanding of this relation that the remaining part of the thesis tries to deepen and around which the second question revolves. This more empirical question (2)is examined through a comparative analysis of a physical original—the 17th century album amicorum of Gottfried Schröer—and its digitisation in the platform Alvin.The informative dimensions “context”, “materiality”, “textbased information”, and the category “aura” are investigated in the original and in the digital reproduction. For this purpose, Walter Benjamin’s concept “aura” is critically discussed and redefined as an analytical concept, and the research question is rephrased in terms of (a) which qualities are transfered, (b) not transfered, and (c) if/how they are transformed during the transfer to the digital format. It is also asked which consequences this might have for the artefact as a source of information. The analysis is positioned in a materiality discourse, adopting perspectives from, i.a., Actor-Network Theory and Material Philology. In this context, a widened concept of materiality is also developed, allowing the inclusion of the “virtual”. The thesis identifies aspects in which the reproduction differs from the original, depending, among other things, on its own materiality. This strengthens the call for users’ information competency when interacting with digital reproductions. This is a two years masters's thesis in library and information science.