Scalable video coding is a powerful solution for content delivery in many interactive multimedia services due to its adaptability to varying terminal and network constraints. In order to successfully exploit such adaptability, it is necessary to understand users' preference among various scalability options and consequently develop an optimal bit rate adaptation strategy. In this paper, we present a study of subjective quality assessment of scalable video coding, which investigates the influence of the combination of scalability options on perceived quality with the goal of providing guidelines for an adaptive strategy that selects the optimal combination for a given bandwidth constraint. In particular, the study is based on paired comparison of stimuli that is suitable for our goal due to its simplicity and easiness. We propose a new method, called Paired Evaluation via Analysis of Reliability (PEAR), which analyzes paired comparison results and produces not only quality scores but also intuitive measures of confidence of the scores for significance analysis. Results and analysis of extensive subjective tests for two different scalable video codecs and high definition contents are described, from which general consistent conclusions are drawn. The video and subjective data used in the paper are publicly available to the research community.

Stereoscopic three-dimensional (3-D) services do not always prevail when compared with their two-dimensional (2-D) counterparts, though the former can provide more immersive experience with the help of binocular depth. Various specific 3-D artefacts might cause discomfort and severely degrade the Quality of Experience (QoE). In this paper, we analyze one of the most annoying artefacts in the visualization stage of stereoscopic imaging, namely, crosstalk, by conducting extensive subjective quality tests. A statistical analysis of the subjective scores reveals that both scene content and camera baseline have significant impacts on crosstalk perception, in addition to the crosstalk level itself. Based on the observed visual variations during changes in significant factors, three perceptual attributes of crosstalk are summarized as the sensorial results of the human visual system (HVS). These are shadow degree, separation distance, and spatial position of crosstalk. They are classified into two categories: 2-D and 3-D perceptual attributes, which can be described by a Structural SIMilarity (SSIM) map and a filtered depth map, respectively. An objective quality metric for predicting crosstalk perception is then proposed by combining the two maps. The experimental results demonstrate that the proposed metric has a high correlation (over 88%) when compared with subjective quality scores in a wide variety of situations.

In 2019, the JPEG Standardization Committee initiated JPEG AI to define the first image coding specifications, taking advantage of an end-to-end learning-based coding approach. The JPEG AI specifications will be soon published as an international standard in early 2025. JPEG AI exploits the current state of the art in deep learning while taking into account considerations for a deployment in the near future. Therefore, JPEG AI design was refined in several iterations to reach the level of maturity and feasibility to both encode and decode images on mobile devices. JPEG AI offers several benefits when compared to previous conventional coding systems, namely the following: 1) superior rate-distortion performance for perceptual visual quality; 2) much faster coding capability; and 3) the possibility of multipurpose optimization, such as coding for both humans and machines. JPEG AI is based on a learning-based image coding algorithm that can generate a single-stream, compact compressed domain representation, targeting both human visualization, with significant compression efficiency improvement over image coding standards, and effective performance for image processing and computer vision tasks, with the goal of supporting a royalty-free baseline. This article describes how such an objective was achieved in version 1 of the JPEG AI standard by providing technical principles behind its design while giving insights on future steps planned for future extensions of JPEG AI.