Light Field Super-Resolution Via Graph-Based Regularization

Light field cameras capture the 3D information in a scene with a single exposure. This special feature makes light field cameras very appealing for a variety of applications: from post-capture refocus, to depth estimation and image-based rendering. However, light field cameras suffer by design from strong limitations in their spatial resolution, which should therefore be augmented by computational methods. On the one hand, off-the-shelf single-frame and multi-frame super-resolution algorithms are not ideal for light field data, as they do not consider its particular structure. On the other hand, the few super-resolution algorithms explicitly tailored for light field data exhibit significant limitations, such as the need to estimate an explicit disparity map at each view. In this work we propose a new light field super-resolution algorithm meant to address these limitations. We adopt a multi-frame alike super-resolution approach, where the complementary information in the different light field views is used to augment the spatial resolution of the whole light field. We show that coupling the multi-frame approach with a graph regularizer, that enforces the light field structure via nonlocal self similarities, permits to avoid the costly and challenging disparity estimation step for all the views. Extensive experiments show that the new algorithm compares favorably to the other state-of-the-art methods for light field super-resolution, both in terms of PSNR and visual quality.Comment: This new version includes more material. In particular, we added: a new section on the computational complexity of the proposed algorithm, experimental comparisons with a CNN-based super-resolution algorithm, and new experiments on a third datase

Spherical clustering of users navigating 360{\deg} content

In Virtual Reality (VR) applications, understanding how users explore the omnidirectional content is important to optimize content creation, to develop user-centric services, or even to detect disorders in medical applications. Clustering users based on their common navigation patterns is a first direction to understand users behaviour. However, classical clustering techniques fail in identifying these common paths, since they are usually focused on minimizing a simple distance metric. In this paper, we argue that minimizing the distance metric does not necessarily guarantee to identify users that experience similar navigation path in the VR domain. Therefore, we propose a graph-based method to identify clusters of users who are attending the same portion of the spherical content over time. The proposed solution takes into account the spherical geometry of the content and aims at clustering users based on the actual overlap of displayed content among users. Our method is tested on real VR user navigation patterns. Results show that our solution leads to clusters in which at least 85% of the content displayed by one user is shared among the other users belonging to the same cluster.Comment: 5 pages, conference (Published in: ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)

Heterogeneous Chemistry of Cl2O and HOCl on Frozen Natural Sea Salt, Recrystallized Sea Salt, KCl and NaCl Solutions at 200 and 215K

The HOCl heterogeneous reaction on frozen natural (NSS) and recrystallized (RSS) sea salt, KCl and NaCl solutions was studied using a low pressure flow reactor in order to measure the uptake coefficient γ and products of reaction. The HOCl sample used in these experiments always contained up to 25% Cl2O which was also studied separately as a pure gas in order to understand the heterogeneous chemistry of both gases. By performing HOCl uptake on frozen NSS solution at 200K and a gas-phase residence time of (1.6±0.6) s we obtained a steady state uptake coefficient γHOCl on NSS = (2.5±0.7)×10-3 and γCl2O on NSS = (2.8±0.8)×10-3. On frozen KCl solution at 200K we obtain γHOCl on KCl = (2.8±1.3)×10-3, identical to NSS, and γCl2O on KCl = (4.6±0.8)×10-4. The main product formed during the uptake on frozen NSS solution is Cl2 which is sustained for at least one hour. In contrast, only a transient Cl2 flow (pulse) decreasing on the time scale of 100s was observed on frozen KCl (NaCl) solution. 25±10% of the HOCl taken up on all chloride-containing frozen substrates at 200K react to produce Cl2 at high HOCl concentration (4.5×1011moleculecm-3) and at a residence time of 1.6s in comparison with twice that for Cl2O. For smaller concentrations such as [HOCl] = 3.7×1010moleculecm-3 and/or a shorter residence time (0.137±0.004s), HOCl uptake did not generate Cl2 in contrast to Cl2O. A single Br2 burst event was monitored when a Cl2O or HOCl/Cl2O mixture is taken up on fresh frozen NSS solution during the first uptake at 200K. Further Cl2O or HOCl/Cl2O uptake on the same sample, even after annealing at 240K does not show an additional Br2 pulse. This Br2 release may be significant in the autocatalytic ozone destruction mechanism in the troposphere during polar sunrise. Some of the atmospheric implications of the present results are highlighted with emphasis on the preequilibrium Cl2O(ads) + H2O(ice) ↔ 2 HOCl(ads) between adsorbed HOCl and Cl2O, with the latter being the gateway to reactive uptake of HOCl at low temperature

A reassessment of prebiotically relevant chemical agents for the activation of α-amino acids and peptides

International audienceFrom an origin-of-life perspective, processes able to provide energy to feed self-organizing systems are required for the formation of their own components but also to maintain a far from equilibrium state essential for the system to remain under kinetic control. α-Amino acid N-carboxyanhydrides (NCAs) and 5(4H)-oxazolones represent activated intermediates of the chemistry of peptides that may be involved in the self-organization of life and in the evolution of translation. An experimental survey of previously published activating agents has been carried out using the epimerization associated with the transient formation of 5(4H)-oxazolones as a tool to monitor their potential to promote strong activation. None of reagents investigated in this survey proved to be totally satisfactory demonstrating that the identification of activation processes remains a crucial goal in this field

Gender and socioeconomic disparities in BMI trajectories in the Seychelles: a cohort analysis based on serial population-based surveys

ABSTRACT: BACKGROUND: The relationship between body mass index (BMI) and socioeconomic status (SES) tends to change over time and across populations. In this study, we examined, separately in men and women, whether the association between BMI and SES changed over successive birth cohorts in the Seychelles (Indian Ocean, African region). METHODS: We used data from all participants in three surveys conducted in 1989, 1994 and 2004 in independent random samples of the population aged 25-64 years in the Seychelles (N= 3'403). We used linear regression to model mean BMI according to age, cohort, SES and smoking status, allowing for a quadratic term for age to account for a curvilinear relation between BMI and age and interactions between SES and age and between SES and cohorts to test whether the relation between SES and BMI changed across subsequent cohorts. All analyses were performed separately in men and women. RESULTS: BMI increased with age in all birth cohorts. BMI was lower in men of low SES than high SES but was higher in women of low SES than high SES. In all SES categories, BMI increased over successive cohorts (1.24 kg/m2 in men and 1.51 kg/m2 for a 10-year increase in birth cohorts, p <0.001). The difference in BMI between men or women of high vs. low SES did not change significantly across successive cohorts (the interaction between SES and year of birth of cohort was statistically not significant). Smoking was associated with lower BMI in men and women (respectively -1.55 kg/m2 and 2.46 kg/m2, p <0.001). CONCLUSIONS: Although large differences exist between men and women, social patterning of BMI did not change significantly over successive cohorts in this population of a middle-income country in the African region

Graph-Based Light Field Super-Resolution

Light field cameras can capture the 3D information in a scene with a single exposure. This special feature makes light field cameras very appealing for a variety of applications: from post capture refocus, to depth estimation and image-based rendering. However, light field cameras exhibit a very limited spatial resolution, which should therefore be increased by computational methods. Off-the-shelf single-frame and multi-frame super-resolution algorithms are not ideal for light field data, as they ignore its particular structure. A few super-resolution algorithms explicitly devised for light field data exist, but they exhibit significant limitations, such as the need to carry out an explicit disparity estimation step for one or several light field views. In this work we present a new light field super-resolution algorithm meant to address these limitations. We adopt a multi- frame alike super-resolution approach, where the information in the different light field views is used to augment the spatial resolution of the whole light field. In particular, we show that coupling the multi-frame paradigma with a graph regularizer that enforces the light field structure permits to avoid the costly and challenging disparity estimation step. Our experiments show that the proposed method compares favorably to the state-of-the- art for light field super-resolution algorithms, both in terms of PSNR and visual quality

Sex difference and the role of leptin in the association between high-sensitivity C-reactive protein and adiposity in two different populations

Elevated high-sensitivity C-reactive protein (hs-CRP) concentration is associated with an increased risk of cardiovascular disease but this association seems to be largely mediated via conventional cardiovascular risk factors. In particular, the association between hs-CRP and obesity has been extensively demonstrated and correlations are stronger in women than men. We used fractional polynomials—a method that allows flexible modeling of non linear relations—to investigate the dose/response mathematical relationship between hs-CRP and several indicators of adiposity in Caucasians (Switzerland) and Africans (Seychelles) surveyed in two population-based studies. This relationship was non-linear exhibiting a steeper slope for low levels of hs-CRP and a higher level in women. The observed sex difference in the relationship between hs-CRP and adiposity almost disappeared upon adjustment for leptin, suggesting that these sex differences might be partially mediated, by leptin. All these relationship were similar in Caucasians and Africans. This is the first report on a non-linear relation, stratified by gender, between hs-CRP and adiposit