Péter András Kara

Viva la resolution: the perceivable differences between image resolutions for light field displays

As 3D display technologies are becoming more and more common in commercial, everyday usage, a special type of 3D known as projection-based light field displays is emerging as well. While holding many key characteristics such as field of view or angular resolution, traditional image resolution also plays a major role in the overall determination of user experience, similarly to 2D displays. The paper investigates the perceivable differences between display resolutions, and presents the acceptability of resolution degradation should it be visible. A total of 20 test participants provided subjective assessment in a series of pair comparisons between 5 resolutions for various stimuli. Beyond mean scores, the results are presented in terms of score distribution in this analysis, separately for each and every stimulus.

Perceptual quality of reconstructed medical images on projection-based light field displays

With the appearance of light field displays, users may enjoy a much more natural sensation of 3D experience compared to prior technologies. This type of autostereoscopic, glasses-free visualization allows medical applications to improve both in usability and efficiency. The high angular resolution of medical images is resource-consuming, but can only be reduced while maintaining a sufficient level of overall quality through continuous parallax. A dense image set can also be achieved by applying the synthesis of intermediate views. In this paper we provide the analysis of the effect of reduced angular resolution and image synthesis on Quality of Experience in medical applications. Two separate series of subjective quality assessment measurements were conducted with 20 participants each, one focusing on angular resolution reduction and another one comparing the effect of such reductions with the quality of reconstructed images.

Challenges of future multimedia QoE monitoring for internet service providers

The ever-increasing network traffic and user expectations at reduced cost make the delivery of high Quality of Experience (QoE) for multimedia services more vital than ever in the eyes of Internet Service Providers (ISPs). Real-time quality monitoring, with a focus on the user, has become essential as the first step in cost-effective provisioning of high quality services. With the recent changes in the perception of user privacy, the rising level of application-layer encryption and the introduction and deployment of virtualized networks, QoE monitoring solutions need to be adapted to the fast changing Internet landscape. In this contribution, we provide an overview of state-of-the-art quality monitoring models and probing technologies, and highlight the major challenges ISPs have to face when they want to ensure high service quality for their customers.

Perceived quality of angular resolution for light field displays and the validy of subjective assessment

Angular resolution plays a vital role in the perceived quality when displaying visual content on autostereoscopic 3D displays, since it affects the motion parallax effect. In this paper, we present the results of a subjective quality assessment carried out on a light field display, investigating the perceptual quality of visual content with different angular resolutions. We also address the question of subjective assessment validity, since the visual experience of suboptimal, reduced angular resolution is currently a completely new phenomenon for test participants.

On the edge of the seat: Reduced angular resolution of a light field cinema with fixed observer positions

The smooth motion parallax of light field displays is one of the most critical enablers of the glasses-free auto-stereoscopic 3D experience. This smoothness originates from an acceptable degree of angular resolution, which is derived from the number of views visualized in the given field of view. However, if human observers view the content without any movement, the requirement for angular resolution can be lower. In this paper, we introduce the results of a subjective quality assessment of visual content displayed on a light field cinema. The angular resolution of the content was different in each test condition, and participants were located in fixed positions during the experiment.

The Effect of Light Field Reconstruction and Angular Resolution Reduction on the Quality of Experience

The quality of visual contents displayed on 3D autostereoscopic displays – such as light field displays – essentially depend on factors that are not present in case of 3D stereoscopic or 2D ones, like angular resolution. A higher number of views in a given field of view enables a smoother, continuous motion parallax, but evidently requires more resources to transmit and display. However, in several cases a sufficiently high number of views might not even be available, thus light field reconstruction is required to increase the density of intermediate views. In this paper we introduce the results of a research aiming to measure the perceptual difference between light field reconstruction and different angular resolutions via a series of subjective image quality assessments. The analysis also calls attention to transmission requirements of content for light field displays.

Getting used to or growing annoyed: How perception thresholds and acceptance of frame freezing vary over time in 3D video streaming

In recent years, HTTP video streaming has become a dominant technology for multimedia content consumption. Frame freezing occurring in the video stream is considered one of the key factors affecting the perceptual visual quality at the client side. In this paper we provide an analysis of how frame freezing in 3D video streams is observed over time, addressing the question whether the user starts tolerating freezes or gets irritated by them. The amount of Temporal Information of the video sequences is taken into consideration, since significant differences between adjacent frames can increase the detectability of freezing.

Subjective quality assessment of zooming levels and image reconstructions based on region of interest for light field displays

As Light Field Displays are becoming widely investigated among the research community and are recently entering consumer market, the Quality of Experience reached on such displays plays a more and more essential role in the determination of their value. Apart from the common characteristics of autostereoscopic displays, the level of zoom on a given spatial resolution also affects the subjective quality assessment of the visualized content. In this paper, we present a subjective study on the level of zoom for Light Field Displays. The perceptual effects of reconstruction based on Region of Interest are also taken into consideration due to their direct connection to zooming. Two independent experiments were carried out and they were completed by 20 test participants each, and the results of the subjective evaluation are detailed in this paper. Our work also addresses subjective quality assessment methodologies, as they influence the results obtained by such experiments.

To interpolate or not to interpolate: Subjective assessment of interpolation performance on a light field display

Interpolating virtual views from sparse visual content increases the angular resolution of the visualization. However, such techniques may degrade the image quality through inaccurate view estimation. The smooth motion parallax through increased angular resolution, and image quality are essential components of the overall user experience. The choice of interpolation initiates an unclear trade-off between them. In this paper, we introduce our research on interpolation techniques for 3D light field visualization. We examined the performance and perceived quality of selected algorithms, in a series of subjective quality assessment experiments. Our results show an obvious interpolation technique preference on visual contents with low angular resolutions.

One spoonful or multiple drops investigation of stalling distribution and temporal information for quality of experience over time

The interruptions of playback fluency are considered to be essential phenomena in the degradation of video quality at the users side during the consumption of HTTP streaming services. Indeed, rebuffering can certainly negatively affect the overall experience, however, the extent of annoyance depends on the content and also on the parameters of stalling, like frequency or duration. In this paper we present a subjective video quality assessment measurement in which a series of videos containing different distributions of frame freezing were evaluated by human observers. The selected points of rebuffering were chosen based on their Temporal Information, which can reflect motion content.