Maryam Azimi

HEVC: The New Gold Standard for Video Compression: How Does HEVC Compare with H.264/AVC?

Digital video has become ubiquitous in our everyday lives; everywhere we look, there are devices that can display, capture, and transmit video. The recent advances in technology have made it possible to capture and display video material with ultrahigh definition (UHD) resolution. Now is the time when the current Internet and broadcasting networks do not even have sufficient capacity to transmit large amounts of HD content-Let alone UHD. The need for an improved transmission system is more pronounced in the mobile sector because of the introduction of lightweight HD resolutions (such as 720 pixel) for mobile applications. The limitations of current technologies prompted the International Standards Organization/International Electrotechnical Commission Moving Picture Experts Group (MPEG) and International Telecommunication Union-Telecommunication Standardization Sector Video Coding Experts Group (VCEG) to establish the Joint Collaborative Team on Video Coding (JCT-VC), with the objective to develop a new high-performance video coding standard.

Compression of high dynamic range video using the HEVC and H.264/AVC standards

The existing video coding standards such as H.264/AVC and High Efficiency Video Coding (HEVC) have been designed based on the statistical properties of Low Dynamic Range (LDR) videos and are not accustomed to the characteristics of High Dynamic Range (HDR) content. In this study, we investigate the performance of the latest LDR video compression standard, HEVC, as well as the recent widely commercially used video compression standard, H.264/AVC, on HDR content. Subjective evaluations of results on an HDR display show that viewers clearly prefer the videos coded via an HEVC-based encoder to the ones encoded using an H.264/AVC encoder. In particular, HEVC outperforms H.264/AVC by an average of 10.18% in terms of mean opinion score and 25.08% in terms of bit rate savings.

Compression efficiency of HDR/LDR content

High Dynamic Range (HDR) imaging is capable of delivering a wider range of luminance and color gamut compared to Standard Dynamic Range (SDR), offering to viewers a visual quality of experience close to that of real-life. In this study, we evaluate the quality of coded original HDR streams and HDR streams reconstructed from SDR videos and metadata, both compressed by the HEVC standard. Our evaluations have shown that the single HDR approach is largely preferred over the SDR counterpart.

Bitrate reduction in asymmetric stereoscopic video with low-pass filtered slices

In 3D video compression, similarities between the two views can be helpful in efficient video compression. One way to take advantage of these similarities is to have one of the views at high quality and lower the quality of the other view. In this study, we measured the bitrate reduction resulted from low-pass filtering horizontal slices in both views, with the corresponding slice in the other view kept at the original quality. Results showed that we can reduce the required bitrate for the stereoscopic video while keeping the 3D video quality close to the original video.

Subjective study on asymmetric stereoscopic video with low-pass filtered slices

This paper proposes a new method for asymmetric filtering of stereoscopic video. In traditional asymmetric stereoscopic video coding, the quality of one of the views is reduced while the other view is of original quality. However, this approach is not fair for people with one dominant eye. We propose to address this problem by reducing the quality of horizontal slices in both views. In our approach, we applied low-pass filtering to slices of both views while the corresponding slice in the other view is untouched. Subjective tests show that the quality, sharpness and depth of the low-passed filtered stereo video are close to the original one. We tested a different number of horizontal slices and various levels of filtering for two representative video sequences. Results show that low-pass filtering of the horizontal slices of both views with smoothing on the slice edges is an effective technique for asymmetric stereoscopic videos.

Visual saliency aided High Dynamic Range (HDR) video quality metrics

As High Dynamic Range (HDR) video is emerging as the next revolution in digital entertainment, finding effective ways for measuring its visual quality is of paramount importance. In this paper, we utilize the saliency information derived from an HDR Visual Attention Model (VAM), called LBVS-HDR, for assessing the quality of HDR video content. To this end, this saliency information is incorporated into existing state-of-the-art HDR quality metrics such as the HDR-VDP-2, deltaE2000, mPSNR, and tPSNR as well as the Standard Dynamic Range (SDR) benchmark quality metric, PSNR. The Visual Information Fidelity (VIF) index is also included in our comparisons, as it is reported to perform well for HDR content. Comparing the results of the VAM-aided quality metrics with those of the original ones, we verified that, in general, using saliency prediction for HDR quality assessment improves the performance of all the existing quality metrics. We also observed that the VIF index achieves the highest correlation between the objective and subjective test results.

Rate-distortion optimization for high dynamic range video coding

The genuine viewing quality of High Dynamic Range (HDR) data brought an evolution to content production and display manufacture markets. However, the efficiency of compression and transmission of HDR content still needs to be improved. In this paper we modify the H.264/AVC standard to better characterize HDR content. We propose a new Lagrangian multiplier that strikes a balance between the bit-rate and distortion of the HDR video. The updated Lagrange multiplier was implemented on the H.264/AVC reference software. Our experiment results show that the HDR-VDP2 quality scores of the videos encoded by the HDR-accustomed encoder are higher than the ones encoded with the reference encoder. Moreover, subjective tests confirmed that the visual quality of the compressed HDR videos using our proposed method is higher than the one encoded by the reference codec1.

A hybrid approach for efficient color gamut mapping

Ultra High Definition (UHD) and High Definition (HD) Television standard recommendations support different color gamuts with the HD gamut much smaller than that of the UHD one. To adapt UHD content to the restricted gamut of HD televisions, a process known as gamut mapping is required. This gamut mapping projects out-of-gamut colors inside the targeted color gamut. Gamut mapping can be performed in any color space and using different projection methods. In this paper, we present a hybrid gamut mapping approach which selects one combination of color space and projection method for each UHD color representable. The selection is based on the CIE ΔE2000 metric. Results show improvements in terms of CIE ΔE2000 when comparing original and projected colors over existing methods.

Performance evaluation of single layer HDR video transmission pipelines

Thanks to the recent developments in both High Dynamic Range (HDR) content creation and HDR consumer displays, HDR technology is now mature enough for consumer TV broadcasting. Considering that HDR displays have been introduced to the consumer market just recently, backward compatible broadcasting approaches that can also address the Standard Dynamic Range (SDR) displays are preferred during this transition period. While several backward compatible single layer approaches have been proposed for HDR content delivery, there is no comprehensive study on the subjective quality of the delivered content on both SDR and HDR displays. In this work, we investigate the performance of two single layer HDR delivery pipelines, namely HDR10 and SDR10 through three sets of subjective test experiments. The effect of different video preprocessing and post-processing methods used in the HDR10 and SDR10 pipelines on the visual quality of the HDR and SDR outputs is investigated in these comprehensive tests. The analysis of the results shows that the HDR10 pipeline can achieve superior HDR quality compared to that of the SDR10 while the SDR subjective quality of the HDR10 pipeline is comparable to that of the SDR10 pipeline. Therefore, it is concluded that HDR10 can be used as a backward compatible single layer pipeline addressing both HDR and SDR displays. It is also shown in this work that by addressing the display in 4:4:4 mode, the SDR subjective quality of the HDR10 pipeline is further improved compared to the 4:2:0 mode. The findings of this work can be used as guidelines for addressing both HDR and SDR displays with HDR10 pipeline.