Jeong-hoon Park

Block Partitioning Structure in the HEVC Standard

High Efficiency Video Coding (HEVC) is the latest joint standardization effort of ITU-T WP 3/16 and ISO/IEC JTC 1/SC 29/WG 11. The resultant standard will be published as twin text by ITU-T and ISO/IEC; in the latter case, it will also be known as MPEG-H Part 2. This paper describes the block partitioning structure of the draft HEVC standard and presents the results of an analysis of coding efficiency and complexity. Of the many new technical aspects of HEVC, the block partitioning structure has been identified as representing one of the most significant changes relative to previous video coding standards. In contrast to the fixed size 16 × 16 macroblock structure of H.264/AVC, HEVC defines three different units according to their functionalities. The coding unit defines a region sharing the same prediction mode, e.g., intra and inter, and it is represented by the leaf node of a quadtree structure. The prediction unit defines a region sharing the same prediction information. The transform unit, specified by another quadtree, defines a region sharing the same transformation. This paper introduces technical details of the block partitioning structure of HEVC with an emphasis on the method of designing a consistent framework by combining the three different units together. Experimental results are provided to justify the role of each component of the block partitioning structure and a comparison with the H.264/AVC design is performed.

Sample Adaptive Offset in the HEVC Standard

This paper provides a technical overview of a newly added in-loop filtering technique, sample adaptive offset (SAO), in High Efficiency Video Coding (HEVC). The key idea of SAO is to reduce sample distortion by first classifying reconstructed samples into different categories, obtaining an offset for each category, and then adding the offset to each sample of the category. The offset of each category is properly calculated at the encoder and explicitly signaled to the decoder for reducing sample distortion effectively, while the classification of each sample is performed at both the encoder and the decoder for saving side information significantly. To achieve low latency of only one coding tree unit (CTU), a CTU-based syntax design is specified to adapt SAO parameters for each CTU. A CTU-based optimization algorithm can be used to derive SAO parameters of each CTU, and the SAO parameters of the CTU are inter leaved into the slice data. It is reported that SAO achieves on average 3.5% BD-rate reduction and up to 23.5% BD-rate reduction with less than 1% encoding time increase and about 2.5% decoding time increase under common test conditions of HEVC reference software version 8.0.

Improved Video Compression Efficiency Through Flexible Unit Representation and Corresponding Extension of Coding Tools

This paper proposes a novel video compression scheme based on a highly flexible hierarchy of unit representation which includes three block concepts: coding unit (CU), prediction unit (PU), and transform unit (TU). This separation of the block structure into three different concepts allows each to be optimized according to its role; the CU is a macroblock-like unit which supports region splitting in a manner similar to a conventional quadtree, the PU supports nonsquare motion partition shapes for motion compensation, while the TU allows the transform size to be defined independently from the PU. Several other coding tools are extended to arbitrary unit size to maintain consistency with the proposed design, e.g., transform size is extended up to 64 × 64 and intraprediction is designed to support an arbitrary number of angles for variable block sizes. Other novel techniques such as a new noncascading interpolation Alter design allowing arbitrary motion accuracy and a leaky prediction technique using both open-loop and closed-loop predictors are also introduced. The video codec described in this paper was a candidate in the competitive phase of the high-efficiency video coding (HEVC) standardization work. Compared to H.264/AVC, it demonstrated bit rate reductions of around 40% based on objective measures and around 60% based on subjective testing with 1080 p sequences. It has been partially adopted into the first standardization model of the collaborative phase of the HEVC effort.

Quadtree Based Nonsquare Block Structure for Inter Frame Coding in High Efficiency Video Coding

A concept of a quadtree based nonsquare block coding structure is presented in this paper for the emerging High Efficiency Video Coding standard, which includes a quadtree based asymmetric motion partitioning scheme and a nonsquare quadtree transform (NSQT) algorithm. Nonsquare motion partitioning in inter frame coding provides the possibility of getting more accurate prediction results by splitting one coding block into two nonsquare prediction blocks. Contrary to the traditional symmetric motion partitions (SMP), asymmetric motion partitions (AMP) are proposed to improve the coding efficiency, especially for the coding blocks with irregular object boundaries. NSQT is designed for nonsquare prediction blocks (SMP and AMP), which combines square and nonsquare transform blocks in a unified transform structure. It exploits the directional characteristic of an image block to improve the transform efficiency. The combination of nonsquare partitions and NSQT provides high coding flexibility and low implementation cost for both encoder and decoder design. Simulation results show that about 0.9%-2.8% bit-rate saving can be achieved in terms of different configurations, and subjective quality can also be improved.

Motion Compensated Prediction and Interpolation Filter Design in H.265/HEVC

Coding efficiency gains in the new High Efficiency Video Coding (H.265/HEVC) video coding standard are achieved by improving many aspects of the traditional hybrid coding framework. Motion compensated prediction, and in particular the interpolation filter, is one area that was improved significantly over H.264/AVC. This paper presents the details of the interpolation filter design of the H.265/HEVC standard. First, the improvements of H.265/HEVC interpolation filtering over H.264/AVC are presented. These improvements include novel filter coefficient design with an increased number of taps and utilizing higher precision operations in interpolation filter computations. Then, the computational complexity is analyzed, both from theoretical and practical perspectives. Theoretical complexity analysis is done by studying the worst-case complexity analytically, whereas practical analysis is done by profiling an optimized decoder implementation. Coding efficiency improvements over the H.264/AVC interpolation filter are studied and experimental results are presented. They show a 4.0% average bitrate reduction for the luma component and 11.3% average bitrate reduction for the chroma components. The coding efficiency gains are significant for some video sequences and can reach up to 21.7%.

Coding efficiency improvement of HEVC using asymmetric motion partitioning

In this paper, coding efficiency improvement of HEVC using asymmetric motion partitioning (AMP) is provided based on HM-6.0. AMP allows asymmetric shape partition mode of prediction unit (PU) for inter prediction. AMP improves the coding efficiency, since irregular image patterns, which otherwise would be constrained to being represented by a smaller symmetric partition, can now be more efficiently represented without requiring further splitting. For encoder speed up, additional conditions are checked before doing motion estimation for each motion partitions. If the certain conditions are met, additional motion estimation, which is main source of encoder complexity for AMP, can be skipped. Experimental results demonstrate that AMP with encoding speed-up shows 0.8% coding efficiency improvement with 14% encoding time increase. Especially for videoconference sequences, coding efficiency improvement reaches to 1.4%.

Generic uneven level protection algorithm for multimedia data transmission over packet-switched networks

To achieve more efficient usage of channel bandwidth and provide better protection for the media payload transmitted over lossy packet-switched networks, we introduce a new scheme of generic uneven level protection (ULP) forward error correction. The scheme provides different protection levels for data of different significance within a packet. The ULP scheme is designed to be independent from the nature of the media that it protects, and it is very flexible for any protection configuration the user might need without using any out-of-band signaling. Simulation using a video stream transmitted over a lossy packet-switched network shows that the ULP algorithm achieves significant gain for the quality of the transmission over a wide range of network conditions.

High precision probability estimation for CABAC

Entropy coding is the main important part of all advanced video compression schemes. Context-adaptive binary arithmetic coding (CABAC) is entropy coding used in H.264/MPEG-4 AVC and H.265/HEVC standards. Probability estimation is the key factor of CABAC performance efficiency. In this paper high accuracy probability estimation for CABAC is presented. This technique is based on multiple estimations using different models. Proposed method was efficiently realized in integer arithmetic. High precision probability estimation for CABAC provides up-to 1,4% BD-rate gain.

Interpolation filter design in HEVC and its coding efficiency - complexity analysis

Coding efficiency gains in the High Efficiency Video Coding (H.265/HEVC) standard are achieved by improving many aspects of the traditional hybrid coding framework. Motion compensated prediction, and in particular the interpolation filter, is one of the areas that was improved significantly over H.264/AVC. This paper presents the details of the motion compensation interpolation filter design of the H.265/HEVC standard and its improvements over the interpolation filter design of H.264/AVC. These improvements include discrete cosine transform based filter coefficient design, utilizing longer filter taps for luma and chroma interpolation and using higher precision operations in the intermediate computations. The computational complexity of HEVC interpolation filter is also analyzed both from theoretical and practical perspectives. Experimental results show that a 4.5% average bitrate reduction for the luma component and 13.0% average bitrate reduction for the chroma components are achieved compared to interpolation filter of H.264/AVC. The coding efficiency gains are significant for some video sequences and can reach up to 21.7%.

Inter-layer filtering for scalable extension of HEVC

This paper introduces inter-layer filters for the scalable extension of High Efficiency Video Coding (SHVC) standard, which is being developed by the Joint Collaborative Team on Video Coding (JCT-VC). The major new coding tool in SHVC is inter-layer texture prediction. It provides about 18% average BD-rate reduction compared with HEVC two-layer simulcast. In the case of spatial scalability, base layer reconstructed pictures are up-sampled to the enhancement layer resolution to generate inter-layer texture prediction. A set of 2D separable 8 taps (luma) and 4 taps (chroma) DCT based interpolation filters, which follow the design principles of HEVC motion compensation interpolation filter, are used in the up-sampling process. In the case of SNR scalability, the up-sampling process is not needed since the reference layer has the same spatial resolution as the current layer but encoded with lower quality. This paper proposes a novel inter-layer filter with denoising effect for SNR scalability to improve enhancement layer coding efficiency and equalize the number of stages in inter-layer processing between SNR and spatial scalabilities. Experimental results show that the usage of inter-layer de-noising filter in SNR scalability provides up to 7.5% BD-rate reduction and has observable improvement on subjective visual quality.