Omnidirectional (or 360°) images and videos are emergent signals being used in many areas, such as robotics and virtual/augmented reality. In particular, for virtual reality applications, they allow an immersive experience in which the user can interactively navigate through a scene with three degrees of freedom, wearing a head-mounted display. Current approaches for capturing, processing, delivering, and displaying 360° content, however, present many open technical challenges and introduce several types of distortions in the visual signal. Some of the distortions are specific to the nature of 360° images and often differ from those encountered in classical visual communication frameworks. This paper provides a first comprehensive review of the most common visual distortions that alter 360° signals going through the different processing elements of the visual communication pipeline. While their impact on viewers’ visual perception and the immersive experience at large is still unknown—thus, it is an open research topic—this review serves the purpose of proposing a taxonomy of the visual distortions that can be encountered in 360° signals. Their underlying causes in the end-to-end 360° content distribution pipeline are identified. This taxonomy is essential as a basis for comparing different processing techniques, such as visual enhancement, encoding, and streaming strategies, and allowing the effective design of new algorithms and applications. It is also a useful resource for the design of psycho-visual studies aiming to characterize human perception of 360° content in interactive and immersive applications.

Visual Distortions in 360° Videos

This paper presents a dynamic radiation pattern diversity (DRPD) MIMO wireless system where the antennas radiation patterns are electronically controlled in real-time. The adopted antenna elements are composite right/left-handed (CRLH) microstrip leaky-wave (LW) antennas for which the beam direction can be electronically scanned in a continuous manner from backfire to endfire and the beam shape can be controlled. This system offers a tremendous amount of flexibility in tuning the channel transfer matrix to increase the system performance. Based on this architecture, we propose two simple radiation pattern control algorithms. The first one requires no feedback and averages out the channel fades while the second one requires a simple feedback at the receiver to select the beam pattern maximizing the performance metric. The capacity of both algorithms is derived and analyzed using Monte Carlo simulations. The results show that these algorithms significantly improve the wireless link outage performance in a slow fading environment and increase the diversity gain of a MIMO system for a fixed multiplexing gain.

Dynamic radiation pattern diversity (DRPD) MIMO using CRLH leaky-wave antennas

In this paper, a three dimensional geometrical scattering channel model for indoor and outdoor wireless propagation environments is introduced. It is based on the assumption that the scatterers are distributed within a spheroid, in which the mobile station and base station are located at the spheroid’s foci. This model captures both the spatial and temporal statistical distributions of the received multipath signals. Several angle of arrival and time of arrival probability density functions of the received multipath signals are provided in compact forms. The angle of arrival probability density functions are obtained in terms of both the azimuth and elevation angles. Numerical results are presented to illustrate and verify the derived expressions. To validate the model, it has been compared against some of the available two dimensional models and measured data. Received 11 August 2010, Accepted 6 October 2010, Scheduled 21 October 2010 Corresponding author: Mohammad Alsehaili (msehaili@ee.umanitoba.ca). 192 Alsehaili et al.

/pdf/angle-and-time-of-arrival-statistics-of-a-three-dimensional-37jv7wteg0.pdf

Angle and time of arrival statistics of a three dimensional geometrical scattering channel model for indoor and outdoor propagation environments

Edge-preserving guided filtering based cost aggregation for stereo matching

Different camera configurations to capture panoramic images and videos are commercially available today. However, capturing omnistereoscopic snapshots and videos of dynamic scenes is still an open problem. Several methods to produce stereoscopic panoramas have been proposed in the last decade, some of which were conceived in the realm of robot navigation and three-dimensional (3-D) structure acquisition. Even though some of these methods can estimate omnidirectional depth in real time, they were not conceived to render panoramic images for binocular human viewing. Alternatively, sequential acquisition methods, such as rotating image sensors, can produce remarkable stereoscopic panoramas, but they are unable to capture real-time events. Hence, there is a need for a panoramic camera to enable the consistent and correct stereoscopic rendering of the scene in every direction. Potential uses for a stereo panoramic camera with such characteristics are free-viewpoint 3-D TV and image-based stereoscopic telepresence, among others. A comparative study of the different cameras and methods to create stereoscopic panoramas of a scene, highlighting those that can be used for the real-time acquisition of imagery and video, is presented.

http://ruor.uottawa.ca/bitstream/10393/30644/1/Gurrieri_L_and_Dubois_E_2013_article.pdf

Acquisition of omnidirectional stereoscopic images and videos of dynamic scenes: a review

A high-resolution channel sounding technique has been used to investigate the cross-polarization of electromagnetic waves in the 5-6 GHz band. Experiments were performed in two non-line-of-sight indoor locations, and it was found that there is a strong dependency of the cross-polarization of multipath components on the elevation angle-of-arrival. For a vertically polarized transmitting antenna, clusters of co-polarized multipath components were confined predominantly to the region around the horizontal plane that contains the virtual line-of-sight between transmitter and receiver. In contrast, cross-polarized signals were detected for a variety of elevation angles with considerable power levels. The surroundings of the receiver were identified as the principal source of depolarized signals. In addition, time dispersion analysis of the multipath signals led to the determination of the AoAs where there is a strong correspondence between co- and cross-polarized signals as a consequence of the partial depolarization of MPCs. This work supports the exploitation of the joint space and polarization diversities in indoor propagation scenarios to improve the system performance.

https://www.ruor.uottawa.ca/bitstream/10393/19657/1/Gurrieri_Luis_2008_Characterization_of_the_Angle_Delay_and.pdf

Characterization of the Angle, Delay and Polarization of Multipath Signals for Indoor Environments

There are different panoramic techniques to produce outstanding stereoscopic panoramas of static scenes. However, a camera configuration capable to capture omnidirectional stereoscopic snapshots and videos of dynamic scenes is still a subject of research. In this paper, two multiple-camera configurations capable to produce high-quality stereoscopic panoramas in real-time are presented. Unlike existing methods, the proposed multiple-camera systems acquire all the information necessary to render stereoscopic panoramas at once. The first configuration exploits micro-stereopsis arising from a narrow baseline to produce omni-stereoscopic images. The second panoramic camera uses an extended baseline to produce poly-centric panoramas and to extract additional depth information, e.g., disparity and occlusion maps, which are used to synthesize stereoscopic views in arbitrary viewing directions. The results of emulating both cameras and the pros and cons of each set-up are presented in this paper.

https://www.ruor.uottawa.ca/bitstream/10393/23947/1/Gurrieri_spcamera_sda2013.pdf

Stereoscopic cameras for the real-time acquisition of panoramic 3D images and videos

A key problem in telepresence systems is how to effectively emulate the subjective experience of being there delivered
by our visual system. A step toward visual realism can be achieved by using high-quality panoramic snapshots instead of
computer-based models of the scene. Furthermore, a better immersive illusion can be created by enabling the free viewpoint
stereoscopic navigation of the scene, i.e. using omnistereoscopic imaging. However, commonly found implementation
constraints of telepresence systems such as acquisition time, rendering complexity, and storage capacity, make the idea of
using stereoscopic panoramas challenging. Having these constraints in mind, we developed a technique for the efficient
acquisition and rendering of omnistereoscopic images based on sampling the scene with clusters of three panoramic images
arranged in a controlled geometric pattern. Our technique can be implemented with any off-the-shelf panoramic cameras.
Furthermore, it does not require neither the acquisition of additional depth information of the scene nor the estimation of
camera parameters. The low the computational complexity and reduced data overhead of our rendering process make it
attractive for the large scale stereoscopic sampling in a variety of scenarios.

http://www.ruor.uottawa.ca/bitstream/10393/20731/1/gurrieri_dubois_2012_efficient_stereoscopic_panoramas.pdf

Efficient panoramic sampling of real-world environments for image-based stereoscopic telepresence

In recent years, the problem of acquiring omnidirectional stereoscopic imagery of dynamic scenes has gained commercial interest, and consequently, new techniques have been proposed to address this problem. The goal of many of these new panoramic methods is to provide practical solutions for acquiring real-time omni- directional stereoscopic imagery for human viewing. However, there are problems related to mosaicking partially overlapped stereoscopic snapshots of the scene that need to be addressed. Among these issues are the con- ditions to provide a consistent depth illusion over the whole scene and the appearance of undesired vertical disparities. We develop an acquisition model capable of describing a variety of omnistereoscopic imaging sys- tems and suitable to study the design constraints of these systems. Based on this acquisition model, we compare different acquisition approaches based on mosaicking partial stereoscopic views of the scene in terms of their depth continuity constraints and the appearance of vertical disparities. This work complements and extends our previous work in omnistereoscopic imaging systems by proposing a mathematical framework to contrast differ- ent acquisition strategies to create stereoscopic panoramas using a small number of stereoscopic images.©2014 SPIE and IS&T (DOI: 10.1117/1.JEI.23.1.011004)

http://www.ruor.uottawa.ca/bitstream/10393/30643/1/Gurrieri_L_E_and_Dubois_E_2014_Depth_consistency_and_vertical_disparities_in_stereoscopic_panoramas.pdf

Luis E. Gurrieri

Papers

Acquisition of omnidirectional stereoscopic images and videos of dynamic scenes: a review

Characterization of the Angle, Delay and Polarization of Multipath Signals for Indoor Environments

Stereoscopic cameras for the real-time acquisition of panoramic 3D images and videos

Efficient panoramic sampling of real-world environments for image-based stereoscopic telepresence

Depth consistency and vertical disparities in stereoscopic panoramas