https://research-explorer.ista.ac.at 2000-01-01T00:00+00:00 1 monthly https://research-explorer.ista.ac.at/record/9819 Mallikarjun, B. R. Tewari, Ayush Dib, Abdallah Weyrich, Tim Bickel, Bernd ; https://orcid.org/0000-0001-6511-9385 Seidel, Hans Peter Pfister, Hanspeter Matusik, Wojciech Chevallier, Louis Elgharib, Mohamed A. Theobalt, Christian 2021 Photorealistic editing of head portraits is a challenging task as humans are very sensitive to inconsistencies in faces. We present an approach for high-quality intuitive editing of the camera viewpoint and scene illumination (parameterised with an environment map) in a portrait image. This requires our method to capture and control the full reflectance field of the person in the image. Most editing approaches rely on supervised learning using training data captured with setups such as light and camera stages. Such datasets are expensive to acquire, not readily available and do not capture all the rich variations of in-the-wild portrait images. In addition, most supervised approaches only focus on relighting, and do not allow camera viewpoint editing. Thus, they only capture and control a subset of the reflectance field. Recently, portrait editing has been demonstrated by operating in the generative model space of StyleGAN. While such approaches do not require direct supervision, there is a significant loss of quality when compared to the supervised approaches. In this paper, we present a method which learns from limited supervised training data. The training images only include people in a fixed neutral expression with eyes closed, without much hair or background variations. Each person is captured under 150 one-light-at-a-time conditions and under 8 camera poses. Instead of training directly in the image space, we design a supervised problem which learns transformations in the latent space of StyleGAN. This combines the best of supervised learning and generative adversarial modeling. We show that the StyleGAN prior allows for generalisation to different expressions, hairstyles and backgrounds. This produces high-quality photorealistic results for in-the-wild images and significantly outperforms existing methods. Our approach can edit the illumination and pose simultaneously, and runs at interactive rates. https://research-explorer.ista.ac.at/record/9819 https://research-explorer.ista.ac.at/download/9819/9834 eng Association for Computing Machinery info:eu-repo/semantics/altIdentifier/doi/10.1145/3450626.3459765 info:eu-repo/semantics/altIdentifier/issn/0730-0301 info:eu-repo/semantics/altIdentifier/e-issn/1557-7368 info:eu-repo/semantics/altIdentifier/wos/000674930900011 info:eu-repo/semantics/altIdentifier/arxiv/2103.07658 info:eu-repo/semantics/openAccess Mallikarjun BR, Tewari A, Dib A, et al. PhotoApp: Photorealistic appearance editing of head portraits. <i>ACM Transactions on Graphics</i>. 2021;40(4). doi:<a href="https://doi.org/10.1145/3450626.3459765">10.1145/3450626.3459765</a> ddc:000 PhotoApp: Photorealistic appearance editing of head portraits info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/19903 Hübner, Valentin ; https://orcid.org/0009-0001-5009-4987 2025 Cooperation, that is, one person paying a cost for another's benefit, is a fundamental principle without which no form of society could exist. The extent to which humans cooperate with each other is also an essential feature that differentiates them from other animals. Cooperation occurs even in the absence of altruistic motivations, when it is selfishly incentivised by the expectation of a future reward. For example, many economic interactions are well described that way. This kind of cooperation requires that people exhibit reciprocal behaviour that acts as a mechanism that rewards cooperation. With game-theoretic models, it is possible to formally study potential such mechanisms and under what conditions they can exist. This thesis contributes to this effort by analysing recently introduced models of cooperation that advance on previous work by taking into account the potential for pre-existing inequality among cooperating individuals as well as the different forms that reciprocity can take. Individuals may differ both intrinsically, in their abilities, as well as extrinsically, in the amount of resources they have available. Allowing for such differences in a model of cooperation helps to understand how inequality affects the potential for, and outcomes of, cooperation among unequals. In this thesis, it is shown that in the presence of intrinsic inequality, a similar unequal distribution of resources can increase the potential for cooperation. This effect is stronger the smaller the group is in which cooperation takes place. It is also shown that under particular assumptions, if the unequal members of a group vary the size of their contributions to a cooperative effort over time, they can thereby increase their efficiency and improve the collective outcome. Cooperative behaviour in a two-person interaction can be rewarded either by direct reciprocation whenever the same two people interact again, or indirectly by a third party who observed the interaction. In the latter case of indirect reciprocity, individuals are proximally rewarded by a good reputation, which ultimately translates to being rewarded with cooperative behaviour by others. This mechanism can enable selfishly motivated cooperation even in circumstances where individuals are unlikely to meet again, akin to how money facilitates trade. While these two forms of reciprocity have mostly been studied in isolation, this thesis analyses both direct and indirect reciprocity in a general model in order to compare their relative effectiveness under different circumstances. The contribution of this thesis is an extension of previous work regarding a specific kind of interaction, whose parameters allow for convenient mathematical analysis, to the most general set of possible interactions. https://research-explorer.ista.ac.at/record/19903 https://research-explorer.ista.ac.at/download/19903/19976 eng Institute of Science and Technology Austria info:eu-repo/semantics/altIdentifier/doi/10.15479/AT-ISTA-19903 info:eu-repo/semantics/altIdentifier/issn/2663-337X info:eu-repo/semantics/openAccess Hübner V. Reciprocity and inequality in social dilemmas. 2025. doi:<a href="https://doi.org/10.15479/AT-ISTA-19903">10.15479/AT-ISTA-19903</a> ddc:519 Reciprocity and inequality in social dilemmas ISTA Thesis info:eu-repo/semantics/doctoralThesis doc-type:doctoralThesis text http://purl.org/coar/resource_type/c_db06 https://research-explorer.ista.ac.at/record/9402 Schmid, Laura ; https://orcid.org/0000-0002-6978-7329 Chatterjee, Krishnendu ; https://orcid.org/0000-0002-4561-241X Hilbe, Christian ; https://orcid.org/0000-0001-5116-955X Nowak, Martin A. 2021 Direct and indirect reciprocity are key mechanisms for the evolution of cooperation. Direct reciprocity means that individuals use their own experience to decide whether to cooperate with another person. Indirect reciprocity means that they also consider the experiences of others. Although these two mechanisms are intertwined, they are typically studied in isolation. Here, we introduce a mathematical framework that allows us to explore both kinds of reciprocity simultaneously. We show that the well-known ‘generous tit-for-tat’ strategy of direct reciprocity has a natural analogue in indirect reciprocity, which we call ‘generous scoring’. Using an equilibrium analysis, we characterize under which conditions either of the two strategies can maintain cooperation. With simulations, we additionally explore which kind of reciprocity evolves when members of a population engage in social learning to adapt to their environment. Our results draw unexpected connections between direct and indirect reciprocity while highlighting important differences regarding their evolvability. https://research-explorer.ista.ac.at/record/9402 https://research-explorer.ista.ac.at/download/9402/14496 eng Springer Nature info:eu-repo/semantics/altIdentifier/doi/10.1038/s41562-021-01114-8 info:eu-repo/semantics/altIdentifier/e-issn/2397-3374 info:eu-repo/semantics/altIdentifier/wos/000650304000002 info:eu-repo/semantics/altIdentifier/pmid/33986519 info:eu-repo/semantics/openAccess Schmid L, Chatterjee K, Hilbe C, Nowak MA. A unified framework of direct and indirect reciprocity. <i>Nature Human Behaviour</i>. 2021;5(10):1292–1302. doi:<a href="https://doi.org/10.1038/s41562-021-01114-8">10.1038/s41562-021-01114-8</a> ddc:000 A unified framework of direct and indirect reciprocity info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/9826 Auerbach, Benedikt ; https://orcid.org/0000-0002-7553-6606 Chakraborty, Suvradip Klein, Karen Pascual Perez, Guillermo ; https://orcid.org/0000-0001-8630-415X Pietrzak, Krzysztof Z ; https://orcid.org/0000-0002-9139-1654 Walter, Michael ; https://orcid.org/0000-0003-3186-2482 Yeo, Michelle X ; https://orcid.org/0009-0001-3676-4809 2021 Automated contract tracing aims at supporting manual contact tracing during pandemics by alerting users of encounters with infected people. There are currently many proposals for protocols (like the “decentralized” DP-3T and PACT or the “centralized” ROBERT and DESIRE) to be run on mobile phones, where the basic idea is to regularly broadcast (using low energy Bluetooth) some values, and at the same time store (a function of) incoming messages broadcasted by users in their proximity. In the existing proposals one can trigger false positives on a massive scale by an “inverse-Sybil” attack, where a large number of devices (malicious users or hacked phones) pretend to be the same user, such that later, just a single person needs to be diagnosed (and allowed to upload) to trigger an alert for all users who were in proximity to any of this large group of devices. We propose the first protocols that do not succumb to such attacks assuming the devices involved in the attack do not constantly communicate, which we observe is a necessary assumption. The high level idea of the protocols is to derive the values to be broadcasted by a hash chain, so that two (or more) devices who want to launch an inverse-Sybil attack will not be able to connect their respective chains and thus only one of them will be able to upload. Our protocols also achieve security against replay, belated replay, and one of them even against relay attacks. https://research-explorer.ista.ac.at/record/9826 eng Springer Nature info:eu-repo/semantics/altIdentifier/doi/10.1007/978-3-030-75539-3_17 info:eu-repo/semantics/altIdentifier/issn/0302-9743 info:eu-repo/semantics/altIdentifier/e-issn/1611-3349 info:eu-repo/semantics/altIdentifier/isbn/9783030755386 info:eu-repo/semantics/openAccess Auerbach B, Chakraborty S, Klein K, et al. Inverse-Sybil attacks in automated contact tracing. In: <i>Topics in Cryptology – CT-RSA 2021</i>. Vol 12704. Springer Nature; 2021:399-421. doi:<a href="https://doi.org/10.1007/978-3-030-75539-3_17">10.1007/978-3-030-75539-3_17</a> Inverse-Sybil attacks in automated contact tracing LNCS info:eu-repo/semantics/conferenceObject doc-type:conferenceObject text http://purl.org/coar/resource_type/c_5794