Quality Assessment in the context of FTV: challenges, first answers and open issues

Traditional acquisition systems record the scene from only one point of view while free-viewpoint television (FTV) or free-viewpoint video (FVV) allows the rendering of a complete representation of the scene. To this aim, it is necessary to use several input cameras, ideally as many as the possible viewing positions of the user. Due to the complexity and cost of such camera set up, a tractable approach consists in acquiring or transmitting only few viewpoints, while intermediate or missing points can be obtained by view interpolation. This is possible thanks to view synthesis techniques that exploit the geometric information of a scene, available for example in MVD (Multiview Video plus Depth) sequences. FTV is an important step towards interactivity since observers can freely change their point of view while exploring the scene. Such capability comes with new technological constraints that must be assessed not only in terms of perceived quality, but especially from the Quality of Experience (QoE) point of view [1]. In fact, FTV brings new issues in QoE assessment, due to the variety of use cases in which this technique can be employed. Furthermore, the free navigation capability is a completely new task in which user experience and QoE assessment methodology have both to be investigated, revisiting traditional approaches. In the following, an overview of the artefacts caused by virtual views generation, together with some options for content exploration are presented. Then, the state of the art on testing protocols and objective quality metrics to assess the quality of rendered FTV views is presented. Finally, we describe available datasets that could support the activities of further objective quality measures development.