The interdependence of spatial and angular resolution in the quality of experience of light field visualization

Light field displays provide a natural sense of 3D visual experience through the glasses-free visualization of the content. It is enabled by the smoothness of the horizontal motion parallax, which is determined by the density of source images allocated to a given field of view. This measure is commonly known as angular resolution, and similarly to spatial resolution, has a fundamental effect on the visual experience. In this paper, we investigate how the reduction of angular and spatial resolution affect each other. Our hypothesis is that lowering spatial resolution to a certain extent does not degrade the perception of the parallax effect, in fact, it may improve it. We carried out a series of subjective tests on a real light field display to test this hypothesis, results of which are introduced in this paper

Comparison of Interactive Subjective Methodologies for Light Field Quality Evaluation

The recent advances in light field acquisition and rendering technologies have attracted a lot of interest from the scientific community. Due to their large amount of data, efficient compression of light field content is of paramount importance for storage and delivery. Quality evaluation plays a major role in assessing the impact of compression on visual perception. In particular, subjective methodologies for light field quality assessment must be carefully designed to ensure reliable results. In this paper, we present and compare two different methodologies to evaluate visual quality of light field contents. Both methodologies allow users to interact with the content and to freely decide which viewpoints to visualize. However, in the second methodology a brief animation of the available viewpoints is presented prior to interaction in order to ensure the same experience for all subjects. The time and patterns of interaction of both methods are compared and analyzed through a rigorous analysis. Conclusions provide useful insights for selecting the most appropriate light field evaluation methodology

Compression and visual quality assessment for light field contents

Since its invention in the 19th century, photography has allowed to create durable images of the world around us by capturing the intensity of light that flows through a scene, first analogically by using light-sensitive material, and then, with the advent of electronic image sensors, digitally. However, one main limitation of both analog and digital photography lays in its inability to capture any information about the direction of light rays. Through traditional photography, each three-dimensional scene is projected onto a 2D plane; consequently, no information about the position of the 3D objects in space is retained. Light field photography aims at overcoming these limitations by recording the direction of light along with its intensity. In the past, several acquisition technologies have been presented to properly capture light field information, and portable devices have been commercialized to the general public. However, a considerably larger volume of data is generated when compared to traditional photography. Thus, new solutions must be designed to face the challenges light field photography poses in terms of storage, representation, and visualization of the acquired data. In particular, new and efficient compression algorithms are needed to sensibly reduce the amount of data that needs to be stored and transmitted, while maintaining an adequate level of perceptual quality. In designing new solutions to address the unique challenges posed by light field photography, one cannot forgo the importance of having reliable, reproducible means of evaluating their performance, especially in relation to the scenario in which they will be consumed. To that end, subjective assessment of visual quality is of paramount importance to evaluate the impact of compression, representation, and rendering models on user experience. Yet, the standardized methodologies that are commonly used to evaluate the visual quality of traditional media content, such as images and videos, are not equipped to tackle the challenges posed by light field photography. New subjective methodologies must be tailored for the new possibilities this new type of imaging offers in terms of rendering and visual experience. In this work, we address the aforementioned problems by both designing new methodologies for visual quality evaluation of light field contents, and outlining a new compression solution to efficiently reduce the amount of data that needs to be transmitted and stored. We first analyse how traditional methodologies for subjective evaluation of multimedia contents can be adapted to suit light field data, and, we propose new methodologies to reliably assess the visual quality while maintaining user engagement. Furthermore, we study how user behavior is affected by the visual quality of the data. We employ subjective quality assessment to compare several state-of-the-art solutions in light field coding, in order to find the most promising approaches to minimize the volume of data without compromising on the perceptual quality. To that means, we define and inspect several coding approaches for light field compression, and we investigate the impact of color subsampling on the final rendered content. Lastly, we propose a new coding approach to perform light field compression, showing significant improvement with respect to the state of the art