Sik-Ho Tsang

Fast wedgelet pattern decision for DMM in 3D-HEVC

3D-HEVC is in the process of standardization as the highest profile extension of HEVC for 3D video coding, which supports the advanced 3D video format, namely multi-view videos plus depth (MVD). In order to preserve the sharp edges and avoid the ringing artifacts in the synthesized views, depth modelling modes (DMMs) are adopted into 3D-HEVC to achieve high coding efficiency. However, the computational complexity increases significantly with these modes. In this paper, an efficient algorithm of wedgelet pattern decision is proposed for one type of the DMMs: the explicit wedgelet signaling or equivalently DMM1. The proposed algorithm roughly estimates the position of sharp edges by pre-defined regions. Then the optimal wedgelet pattern is only searched in the most probable region. Simulation results show that our algorithm saves about 55% time of the wedgelet pattern selection with the BD-Rate increased by 0.49% in average.

Fast and efficient intra coding techniques for smooth regions in screen content coding based on boundary prediction samples

This paper presents fast and efficient intra prediction algorithms for screen content coding (SCC). The proposed algorithms focus on smooth regions frequently appeared in screen content videos, which have the characteristics of noiselessness. All the samples in a noiseless smooth region exhibit exactly the same pixel value. We then propose two intra coding techniques for noiseless smooth regions in SCC based on the smoothness of the boundary samples which are used for intra prediction. Our proposed algorithm can reduce computational complexity by at most 26.7% while keeping nearly the same video quality. Moreover, by removing the redundant coding bits for intra prediction modes, computational complexity can be further reduced to at most 53.3% in terms of encoding time with bitrate reduction up to 1.2%.

Efficient depth intra mode decision by reference pixels classification in 3D-HEVC.

The uniform intra prediction increases the intra prediction modes up to 35 and brings better coding efficiency in HEVC. Besides, depth modelling modes (DMMs) are introduced in depth intra coding of 3D-HEVC to preserve sharp edges and avoid ringing artifacts in a synthesized view. Meanwhile, the encoding time of depth intra coding rapidly increases due to a huge number of intra mode candidates. Based on the spatial correlation of a depth map, we find that not all of the intra modes are necessary to be considered in most cases. Hence, a fast content-dependent depth intra mode decision algorithm is raised in this paper by classifying the spatial distribution of the reference pixels. Simulation results show that the proposed adaptive fast algorithm can save 21%-35% time of the depth coding with the insignificant bit rate increase compared with the state-of-the-art algorithm.

Region-Based Weighted Prediction for Coding Video With Local Brightness Variations

This paper presents a new region-based scheme for the estimation of weighted prediction (WP) parameter sets for encoders of the H.264/MPEG-4 AVC standard. The proposed scheme is specifically designed for handling local brightness variations (LBVs) in video scenes. It is achieved by making use of multiple WP parameter sets for various regions and assigning them to the same reference frame. An accurate estimation of multiple WP parameter sets is accomplished by: 1) partitioning regions with a simple WP parameter estimator; 2) selecting regions where WP should be applied; and 3) estimating accurate WP parameter sets with a quasioptimal WP parameter estimator. The multiple WP parameter sets of different regions are encoded using the framework of multiple reference frames in the H.264/MPEG-4 AVC standard. With this arrangement, the proposed scheme is compliant with the H.264/MPEG-4 AVC standard. To reduce the implementation cost, a reduction of the memory requirement is realized via look-up tables (LUTs). Experimental results show that the region-based scheme can efficiently handle scenes with global and LBVs and achieve significant coding gain over other WP schemes. Furthermore, our scheme with LUTs can reduce the memory requirement by about 80% while keeping the same coding efficiency as that without LUTs.

Adaptive fast intra mode decision of depth map coding by Low Complexity RD-Cost in 3D-HEVC

The coding efficiency of 3D-HEVC can be improved significantly by adopting more intra modes in depth map coding, including up to 35 conventional HEVC intra prediction modes and 4 depth modelling modes (DMMs). However, traversing these modes dramatically results in unendurable high complexity. In this paper, we propose an efficient intra mode decision algorithm by taking advantage of the Low Complexity Rate-Distortion Cost information in the rough mode decision. Only one conventional intra mode and several most probable modes are then selected for most cases adaptively based on the threshold derived from the prior probability. Experimental results show that the proposed algorithm provides about 34% saving in terms of the total depth coding time with little drop of the coding performance compared with the state-of-the-art algorithm.

Hash based fast local search for Intra Block Copy (IntraBC) mode in HEVC screen content coding

The Intra Block Copy (IntraBC) mode is a very efficient coding tool for the screen content coding (SCC) extension in High Efficiency Video Coding (HEVC) due to the frequently occurrences of repeating patterns and noiseless characteristics of screen content videos. There are local search and hash search for the IntraBC mode to increase coding efficiency. However, the IntraBC mode also brings along high computational complexity for SCC as exhaustive block matching is done within the same frame. Though there are already some constraints applied to IntraBC mode to reduce its complexity, it is still very high. To further reduce the complexity, we propose to speed up the local search by checking the hash values of both current block and block candidates. With our proposed methods, the encoding time is reduced by up to 25% and 23% for YUV and RGB sequences respectively while coding efficiency can still be maintained with only negligible bitrate increased.

Probability-Based Depth Intra-Mode Skipping Strategy and Novel VSO Metric for DMM Decision in 3D-HEVC

Multiview video plus depth format has been adopted as the emerging 3D video representation recently. It includes a limited number of textures and depth maps to synthesize additional virtual views. Since the quality of depth maps influences the view synthesis process, their sharp edges should be well preserved to avoid mixing foreground with background. To address this issue, 3D-High Efficiency Video Coding (HEVC) introduces new coding tools, a partition-based intra mode [depth modeling mode (DMM)], a residual description technique [segmentwise depth coding (SDC)], and a more complex rate-distortion (RD) evaluation with view synthesis optimization (VSO), to provide more accurate predictions and achieve higher compression rate. However, these new techniques introduce a lot of possible candidates, and each of them requires complicated RD calculation in the process of intra-mode decision. They lead to unacceptable computational burden in a 3D-HEVC encoder. Therefore, in this paper, we raise two efficient techniques for depth intra-mode decision. First, by investigating the statistical characteristics of variance distributions in the two partitions of DMM, a simple but efficient criterion based on the squared Euclidean distance of variances (SEDV) is suggested to evaluate RD costs of the DMM candidates instead of the time-consuming VSO process. Second, a probability-based early depth intra-mode decision is proposed to select only the most promising mode and make the early determination of using SDC based on the low-complexity RD cost in rough mode decision. Experimental results show that the proposed algorithm with these two new techniques provides 33%–48% time reduction with little drop in the coding performance compared with the state-of-the-art algorithms.

Early determination of intra mode and segment-wise DC coding for depth map based on hierarchical coding structure in 3D-HEVC

This paper proposes a fast algorithm to reduce the high computational complexity of depth map coding in 3D-HEVC, which obstructs 3D video from the practical applications. Due to the special feature of depth maps, depth modelling modes (DMMs) were developed to keep sharp edges for depth map. Consequently, the 3D-HEVC encoder can improve the coding performance of synthesized views significantly. However, this is at the significant cost of increased complexity. Since 3D-HEVC reuses the well-known hierarchical coding structure, the mode information of the parent coding units (CU) can be reused to predict the most probable modes for their CUs. Besides, a method is also proposed for early determination of segment-wise DC coding (SDC) decision based on the hierarchical coding structure. Simulation results show that the proposed algorithm achieves a reduction of 33% encoding time while maintaining the quality of synthesized views in term of bit-rate values.

Quadtree decision for depth intra coding in 3D-HEVC by good feature

3D-HEVC is a good coding solution for multi-view video plus depth data. It achieves good coding performance of synthesized views. However, depth intra coding brings unbearable complexity, which is the most urgent issue to be solved for the practical applications. Typically, depth maps have a good feature of structure or less texture compared with natural videos. Therefore, in this paper, a fast depth intra coding algorithm is proposed to speed up the quadtree decision by the good feature-corner point (CP). The proposed algorithm can adaptively extract CPs and preallocate the depth level of coding quadtree. The large size of coding units (CUs) can be skipped for blocks, which have higher predicted depth level. On the contrary, the blocks, with lower predicted depth level, do not check the smaller size of CUs. Simulation results show that the proposed algorithm can provide about 41% time reduction while maintaining the BD performance.

Fast HEVC screen content coding by skipping unnecessary checking of intra block copy mode based on CU activity and gradient

The Intra Block Copy (IntraBC) mode is a very efficient coding tool for the screen content coding (SCC) extension in High Efficiency Video Coding (HEVC) by finding the repeating patterns within the same frame. Yet, it also brings along impractically high computational complexity for SCC, which can be a double of the conventional HEVC, as exhaustive block matching is done within the same frame even though there are already some constraints applied to the IntraBC mode. To reduce the complexity, we propose to skip the unnecessary IntraBC mode checking based on the activity and gradient within the coding unit (CU). With our proposed methods, the increased encoding time compared with the conventional HEVC is reduced from 90.0% to 62.2% on average while the coding efficiency can still be maintained with only negligible bitrate increased.