This paper presents a new objective quality metric that was adapted to the complex characteristics of immersive video (IV) which is prone to errors caused by processing and compression of multiple input views and virtual view synthesis. The proposed metric, IV-PSNR, contains two techniques that allow for the evaluation of quality loss for typical immersive video distortions: corresponding pixel shift and global component difference. The performed experiments compared the proposal with 31 state-of-the-art quality metrics, showing their performance in the assessment of quality in immersive video coding and processing, and in other applications, using commonly used image quality assessment databases – TID2013 and CVIQ. As presented, IV-PSNR outperforms other metrics in immersive video applications and still can be efficiently used in the evaluation of different images and videos. Moreover, basing the metric on the calculation of PSNR allowed the computational complexity to remain low. Publicly available, efficient implementation of IV-PSNR software was provided by the authors of this paper and is used by ISO/IEC MPEG for evaluation and research on the upcoming MPEG Immersive video (MIV) coding standard.

In this paper, we present a new objective quality metric designed for immersive video applications—IV-SSIM. The proposed IV-SSIM metric is an evolution of our previous work—IV-PSNR (immersive video peak signal-to-noise ratio)—which became a commonly used metric in research and ISO/IEC MPEG standardization activities on immersive video. IV-SSIM combines the advantages of IV-PSNR and metrics based on the structural similarity of images, being able to properly mimic the subjective quality perception of immersive video with its characteristic distortions induced by the reprojection of pixels between multiple views. The effectiveness of IV-SSIM was compared with 16 state-of-the-art quality metrics (including other metrics designed for immersive video). Tested metrics were evaluated in an immersive video coding scenario and against a commonly used image quality database—TID2013—showing their performance in both immersive and typical, non-immersive use cases. As presented, the proposed IV-SSIM metric clearly outperforms other metrics in immersive video applications, while also being highly competitive for 2D image quality assessment. The authors of this paper have provided a publicly accessible, efficient implementation of the proposed IV-SSIM metric, which is used by ISO/IEC MPEG video coding experts in the development of the forthcoming second edition of the MPEG immersive video (MIV) coding standard.

This paper presents the fast virtual view synthesis method for free navigation purposes. Presented method was implemented on CPU in order to allow free navigation for even cheap personal computers with integrated graphic cards. The described synthesis technique is based on the hybrid view synthesis, combining advantages of forward-type and backward-type synthesis. It allows to synthesize high resolution sequences in the real time, allowing the viewer to freely navigate around the scene, e.g. volleyball playfield. Three implementations were developed and tested: single-threaded, vectorized and multithreaded implementation.

In the new HEVC standard, there are 35 intraframe prediction modes. Therefore, real-time implementations need fast mode pre-selection to reduce the computational load of cost comparison for individual modes. In this paper, a simple technique is proposed to reduce the complexity of the Unified Intra Prediction by decreasing the mode candidate number evaluated in the Rough Mode Decision step. We call this approach hierarchical as we decrease stepwise the angles between the directions of the prediction modes that are tested. Obviously, the fast mode selection results in significant complexity reduction obtained at the cost of choosing a sub-optimum mode related to slightly reduced compression performance. In the paper, it is proposed how to calculate the trade-off between encoder complexity and compression performance, using the ratio of relative coding time reduction and average bitrate increase estimated for constant decoded video quality. Extensive experiments prove that this ratio is much higher for the proposed technique than for many other techniques from the references.

Most research results in video watermarking refer to the embedding of messages into uncompressed video, which needs full decoding and then full encoding of the content. In some applications, such a method is too complex, and watermarking of compressed bitstreams is required. Watermarking of compressed bitstreams is more difficult as the number of bits is very limited, and the compressed video is very sensitive to all modifications that may yield visible artifacts in the decoded watermarked video. In the paper, an original watermarking method is described for HEVC-compressed video. The main idea of the technique is to embed a message into nonzero residual transform coefficients in such a way that potential drift is limited. The watermark detection is based on reference, unwatermarked video. The experimental verification demonstrates the strong robustness of the embedded watermarks.