Context-based Quality of Experience in Immersive Multimedia

Since 1895, when the Lumière brothers came out with the projected cinematograph, motion pictures and more generally multimedia contents have considerably improved and are still experiencing a very dynamic development. Advances involved improving various modalities that influence the Human Visual System (HVS) or the human perception. Indeed, migrations concerning audio, resolution, color, brightness, depth representations and frame rate have been performed or are being implemented.

A high-quality multimedia content targets at least an acceptable level of consumer¿s satisfaction. It assumes to be a combination of sensory stimuli whose goal is to entertain, to educate or to inform, and can convey an artistic intent. Measuring the end-user satisfaction is a challenge as it is a complex multi-dimensional concept.

To understand, measure and predict user satisfaction, researchers focused on the perceived quality of multimedia contents. Quality is the expression of an individual comparison and judgment process. It is based on inherent characteristics of a stimulus. It turns out that network-related impairments, major distortions in content delivery, are not considered when evaluating contents¿ inherent features. The quality measure considering the entire service pipeline (including delivery) is referred to as QoS. A more user-centric quality concept has been created under the consideration that not only technical quality and delivery artifacts influence an experience. Accordingly, QoE represents the user¿s degree of delight or annoyance for an application or service in regards to his prior knowledge, expectations and current state.

This work addresses the design of new methodologies for QoE subjective evaluation. The research includes identification, definition and investigation on influence factors of QoE. Possibility to predict QoE using physiological signals gathered during subjective assessment is also considered.

This thesis is positioned as a framework for the assessment of emerging technologies. Its main focus is on HDR and Wide Color Gamut (WCG) representations, for these emerging technologies provide faithful and realistic content; immersive technologies, such as 360 imaging and VR gaming; as well as the combination of typical multimedia representations (e.g. Standard Resolution (SD), High Definition (HD) and 4K contents along with no audio, stereo and surround audio).

From conducted experiments on HDR and WCG, important recommendations came out for these technologies¿ deployment regarding representation and compression strategies while indicating future directions for QoE assessment.

We designed a new subjective methodology for 360¿ HDR contents. It investigates which dimensions should be included in immersive and realistic contents evaluation while considering representation constraints (e.g., no spatial pair comparison possible for 360¿ contents).

Expectations and novelty effect evaluations, two emerging-technologies-related aspects that can bias QoE-centric subjective assessment, have been implemented in the context of Virtual Reality (VR) gaming.

Finally, attempts to predict the SoP, an important QoE-related notion when analyzing physiological signals (brain activity (Electroencephalography (EEG)), heart activity (Electrocardiography (ECG)) and respiration) have been performed for various multimedia consumption scenarios (in terms of quality, resolution and sound systems as well as typical use cases).