Efficient Multi-Strategy Intra Prediction for Quality Scalable High Efficiency Video Coding

Abstract

As an extension of High Efficiency Video Coding (HEVC), the Scalable High Efficiency Video Coding (SHVC) introduces multiple layers with inter-layer predictions, which greatly increases the complexity on top of the already complicated HEVC encoder. In Intra prediction for Quality SHVC, Coding Tree Unit (CTU) allows recursive splitting into four depth levels, which considers 35 Intra prediction modes and interlayer reference (ILR) mode to determine the best possible mode at each depth level. This achieves the highest coding efficiency but incurs a substantially high computational complexity. In this paper, we propose a novel Intra prediction scheme to effectively speed up the enhancement layer Intra-coding in Quality SHVC. The new features of the proposed framework include: First, spatial correlation and its correlation degree are combined to predict most probable depth level candidates. Second, for a given depth candidate, based on the probabilities of the ILR mode, we check the ILR mode by examining the residual distribution based on skewness and kurtosis to determine whether the residuals follow a Gaussian distribution. In that case, the Intra prediction comparisons, which require a high complexity, are skipped. Third, during Intra prediction selection from 35 Intra prediction modes, spatial and inter-layer correlations are combined with the local monotonicity of the Hadamard costs associated with the modes in a small neighborhood, to examine only a portion of Intra prediction modes. Finally, a hypothesis testing on the currently selected depth level is performed to examine whether the residuals present significant differences within their block to early terminate depth selection. The proposed multi-step multistrategy scheme aims to minimize the number of depth selections while greatly reducing the mode decision complexity for a depth candidate in a hierarchical fashion. Our experimental results demonstrate that the proposed scheme can achieve a speedup gain of more than 75% in average on the test video sequences, while maintaining almost the same coding efficiency. .

Fast Depth and Mode Decision in Intra Prediction for Quality SHVC

“…Then, they select directional modes of relative CUs, and the directional mode with the smallest HC cost in mode 2, 10, 18, 26, and 34, as initial modes, and finally combine with the relationship between the modes and HC to obtain the best directional mode. Wang et al [38] first predict candidate depths, then predict the best mode between ILR mode and intra mode in each candidate depth, and finally test whether depth early termination is satisfied to skip other depths to improve the coding speed.…”

“…To meet the diverse requirements for video resolutions, we use test sequences in class B, C, D and E in our experiments, and select two test sequences in each class: Sunflower and Tractor in class B; Flowervase and PartyScene in class C; BlowingBubbles and RaceHorses in class D; and Park and Town in class E. Since we study intra only algorithm for QS, each test sequence is encoded using all I-frame structure. According to common SHM test conditions (CSTC) [39], the QPs used for the BL are set as (26,30,34,38), and the corresponding QPs used for the EL are set as (22,26,30,34) and (20,24,28,32), respectively. Since the performances of the two QP settings are similar, only the experimental results for QPs with (22,26,30,34) are provided for brevity.…”

Fast Depth and Inter Mode Prediction for Quality Scalable High Efficiency Video Coding

“…Tohidypour et al use coding information of relative CUs including neighboring CU in EL and the colocated CU in BL to build a probabilistic model, and then uses this model to predict the candidate modes of the current CU in EL to improve the coding speed [24]. Wang et al [25] predict candidate depths. In each candidate depth, if ILR mode early termination condition is satisfied, intra mode prediction can be skipped; otherwise intra mode prediction needs to be checked.…”

“…Therefore, we adopt Gaussian distribution in this research. In [25], we proposed a test for intra prediction, which is based on skewness and kurtosis detection, to check whether residual coefficients follow the Gaussian distribution. Here, we apply this test to decide whether residual coefficients for inter prediction follow a Gaussian distribution.…”

Fast Inter Mode Predictions for SHVC

“…Tohidypour et al use coding information of relative CUs including neighboring CU in EL and the co-located CU in BL to build a probabilistic model,and then uses the proposed probabilistic model to predict the candidate modes of the current CU in the EL to improve the coding speed [10]. Wang et al [11] predict candidate depths. In each candidate depth, if ILR mode early termination condition is satisfied, intra mode prediction can be skipped; otherwise intra mode prediction needs to be checked.…”