Free-viewpoint video sequences: A new challenge for objective quality metrics

Free-viewpoint television is expected to create a more natural and interactive viewing experience by providing the ability to interactively change the viewpoint to enjoy a 3D scene. To render new virtual viewpoints, free-viewpoint systems rely on view synthesis. However, it is known that most objective metrics fail at predicting perceived quality of synthesized views. Therefore, it is legitimate to question the reliability of commonly used objective metrics to assess the quality of free-viewpoint video (FVV) sequences. In this paper, we analyze the performance of several commonly used objective quality metrics on FVV sequences, which were synthesized from decompressed depth data, using subjective scores as ground truth. Statistical analyses showed that commonly used metrics were not reliable predictors of perceived image quality when different contents and distortions were considered. However, the correlation improved when considering individual conditions, which indicates that the artifacts produced by some view synthesis algorithms might not be correctly handled by current metrics.