Femto-Photography: Capturing Light in Motion

We show a technique to capture ultrafast movies of light in motion and synthesize physically valid visualizations. The effective exposure time for each frame is under two picoseconds (ps). Capturing a 2D video with this time resolution is highly challenging, given the extermely low SNR associated with a picosecond exposure time, as well as the absence of 2D cameras that can provide such a shutter speed. We re-purpose modern imaging hardware to record an ensemble average of repeatable events that are synchronized to a streak tube, and we introduce reconstruction methods to visualize propagation of light pulses through macroscopic scenes. Capturing two-dimensional movies with picosecond resolution, we observe many interesting and complex light transport effects, including multibounce scattering, delayed mirror reflections, and subsurface scattering. We notice that the time instances recorded by the camera, i.e. “camera time” is different from the the time of the events as they happen locally at the scene location, i.e. world time. We introduce a notion of time warp between the two space time coordinate systems, and rewarp the space-time movie for a different perspective

Standardized experimental estimation of the maximum unnoticeable environmental displacement during eye blinks for redirect walking in virtual reality

Redirect walking is a technique that aims to manipulate the walking trajectories in immersive virtual reality settings by inducing unnoticeable displacements of the virtual environment. Taking into advantage the change blindness phenomenon, visual occlusion during eye blinks has been recently proposed to perform those displacements. This study determined the maximum unnoticeable displacement that can be performed in practical scenario, which proved to be near 0.8° of occlusion and disocclusion in both horizontal and vertical axes

Perception of material appearance:Aa comparison between painted and rendered images

Painters are masters in replicating the visual appearance of materials.While the perception of material appearance is not yet fully understood, painters seem to have acquired an implicit understanding of the key visual cues that we need to accurately perceive material properties. In this study, we directly compare the perception of material properties in paintings and in renderings by collecting professional realistic paintings of rendered materials. From both type of images, we collect human judgments of material properties and compute a variety of image features that are known to reflect material properties. Our study reveals that, despite important visual differences between the two types of depiction, material properties in paintings and renderings are perceived very similarly and are linked to the same image features. This suggests that we use similar visual cues independently of the medium and that the presence of such cues is sufficient to provide a good appearance perception of the materials. Copyright 2021 The Author

Microscale thermo-elastic analysis of composite materials by high-order geometrically accurate finite elements

The present work proposes a new approach for conducting thermo-elastic micromechanical analysis. It relies on the use of high-order and geometrically accurate beam finite elements to model the microstructures. The governing equations of the micromechanics models involving the unit cell concept are derived through the Mechanics of Structure Genome (MSG). MSG allows multiscale analysis where global and local scales are decoupled and provides the constitutive information and local fields without needing ad hoc assumptions or requiring different loading steps. The high-order beam elements are derived instead by means of the well-known Carrera Unified Formulation (CUF). These advanced models provide a level of accuracy comparable to conventional solid elements with a fraction of the computational effort. Depending on the problem considered, the cross-section of the refined beam model is modelled by a set of Legendre polynomials, whilst the main direction of the representative unit cell is discretised using one-dimensional (1D) finite elements. Additionally, a non-isoparametric mapping technique allows a perfect description of the microstructural constituents. The present approach enables the resolution of both thermo-elastic homogenisation problems and the recovery of local stress fields through a single run of a CUF-MSG-based code. Several numerical examples compared with numerous other representative solutions of fibre and particle reinforced composites are conducted in order to demonstrate the validity and the efficiency of the presented methodology

Convolutional sparse coding for high dynamic range imaging

Current HDR acquisition techniques are based on either (i) fusing multibracketed, low dynamic range (LDR) images, (ii) modifying existing hardware and capturing different exposures simultaneously with multiple sensors, or (iii) reconstructing a single image with spatially-varying pixel exposures. In this paper, we propose a novel algorithm to recover high-quality HDRI images from a single, coded exposure. The proposed reconstruction method builds on recently-introduced ideas of convolutional sparse coding (CSC); this paper demonstrates how to make CSC practical for HDR imaging. We demonstrate that the proposed algorithm achieves higher-quality reconstructions than alternative methods, we evaluate optical coding schemes, analyze algorithmic parameters, and build a prototype coded HDR camera that demonstrates the utility of convolutional sparse HDRI coding with a custom hardware platform

Multimodality in {VR}: {A} Survey

Virtual reality has the potential to change the way we create and consume content in our everyday life. Entertainment, training, design and manufacturing, communication, or advertising are all applications that already benefit from this new medium reaching consumer level. VR is inherently different from traditional media: it offers a more immersive experience, and has the ability to elicit a sense of presence through the place and plausibility illusions. It also gives the user unprecedented capabilities to explore their environment, in contrast with traditional media. In VR, like in the real world, users integrate the multimodal sensory information they receive to create a unified perception of the virtual world. Therefore, the sensory cues that are available in a virtual environment can be leveraged to enhance the final experience. This may include increasing realism, or the sense of presence; predicting or guiding the attention of the user through the experience; or increasing their performance if the experience involves the completion of certain tasks. In this state-of-the-art report, we survey the body of work addressing multimodality in virtual reality, its role and benefits in the final user experience. The works here reviewed thus encompass several fields of research, including computer graphics, human computer interaction, or psychology and perception. Additionally, we give an overview of different applications that leverage multimodal input in areas such as medicine, training and education, or entertainment; we include works in which the integration of multiple sensory information yields significant improvements, demonstrating how multimodality can play a fundamental role in the way VR systems are designed, and VR experiences created and consumed