Bumshik Lee

A Novel Fast CU Encoding Scheme Based on Spatiotemporal Encoding Parameters for HEVC Inter Coding

Recently, a new video coding standard, High Efficiency Video Coding (HEVC), has shown greatly improved coding efficiency by adopting hierarchical structures of coding unit (CU), prediction unit (PU), and transform unit (TU). To best achieve the coding efficiency, the best combinations of CU, PU, and TU must be found in the sense of the minimum rate-distortion (R-D) costs. Owing to this, a large computational complexity occurs. Among these CU, PU, and TU, the determination of CU sizes most significantly affects the R-D performance of HEVC encoders, which causes large computational costs in operation with PU and TU size determinations. In spite of recent works in the complexity reduction of HEVC encoders, most of the research has focused on the complexity reduction with fast CU split in intra slice coding and with early TU split in both intra and inter slice. In this paper, we propose a fast and an efficient CU encoding scheme based on the spatiotemporal encoding parameters of HEVC encoders, which consists of an improved early CU SKIP detection method and a fast CU split decision method. For the current CU block under encoding, the proposed scheme utilizes sample-adaptive-offset parameters as the spatial encoding parameter to estimate the texture complexity that affects the CU partition. In addition, the motion vectors, TU size, and coded block flag information are used as the temporal encoding parameters to estimate the temporal complexity that also affects the CU partition. The proposed scheme effectively utilizes the spatiotemporal encoding parameters that are the byproducts during the encoding process of HEVC without additionally required computation. The proposed novel fast CU encoding scheme significantly reduces the total encoding time with negligible RD-performance loss. The experimental results show that the proposed scheme achieves the total encoding time savings of average 49.6% and 42.7% only with average 1.4% and 1.0% bit-rate losses for various test sequences under random access and low delay B conditions, respectively. The proposed scheme has an advantage on the implementation for parallel processing in pipeline structures of HEVC encoders due to its independency with neighboring CU blocks.

Modeling Rates and Distortions Based on a Mixture of Laplacian Distributions for Inter-Predicted Residues in Quadtree Coding of HEVC

Inprobability model based rate control of video coding, modeling of residual distribution is important in predicting precise distortions so as to determine appropriate quantization parameter values. For this, single probability model approaches have been popularly taken which may fail to model the underlying statistical characteristics of different residues from variable block-sized coding. In this letter, new rate and distortion models based on a mixture of multiple Laplacian distributions are presented for the transform coefficients of inter-predicted residues in quadtree coding. The proposed mixture model of multiple Laplacian distributions is tested for the High Efficiency Video Coding (HEVC) Test Model (HM) with quadtree-structured Coding Unit and Transform Unit. The experimental results show that the proposed model achieves more accurate results of rate and distortion estimation than the single probability models.

No-Reference PSNR Estimation for HEVC Encoded Video

Video quality estimation is considered a means of monitoring quality of service in broadcasting or IPTV services. In this paper, a no-reference peak signal-to-noise ratio (PSNR) estimation method is first presented for a quadtree-based motion estimation or compensation and transform coding scheme such as HEVC test model (HM), which is expected to be popularly used due to its highly enhanced coding efficiency, in 2-D and 3-D high resolution videos. The proposed no-reference PSNR estimation method is based on a Laplacian mixture distribution, which takes into account the distribution characteristics of residual transform coefficients in different quadtree depths and coding types of coding units (CUs). In order to predict the model parameters of the Laplacian mixture distribution for all zero quantized coefficients case, an exponential regression scheme is employed over quadtree depth levels of CUs. The proposed no-reference PSNR estimation method yields fairly accurate results from 0.970 to 0.983 in correlation and from 0.530 to 0.890 in RMSE between the actual and the estimated PSNR values for HM encoded bitstreams, outperforming single PDF based models.

A fast mode selection scheme in inter-layer prediction of H.264 Scalable Extension coding

We propose a fast inter-layer mode decision method by utilizing coding information of base layer upward its enhancement layer in scalable video coding (SVC), also called MPEG-4 part 10 Advanced Video Coding Amendment 3 or H.264 Scalable Extension (SE). In this paper, when the motion vectors from the base layer have zero motion (0, 0) in inter-layer motion prediction or the Integer Transform coefficients of the residual between current MB and the motion compensated MB by the predicted motion vectors from the base layer are all zero, the block mode of the corresponding block to be encoded in the enhancement layer is determined to be the 16*16 mode. In addition, if the predicted mode of the MB to be encoded at the enhancement layer is not equal to the 16 *16 mode, then the rate-distortion optimization is only performed on the reduced numbers of candidate modes which are same or smaller partitioned modes. Our proposed method exhibits the complexity reduction in encoding time up to 70%. Nevertheless, it shows negligible PSNR degradation and bit rate increase up to 0.2 MB and 0.71 % respectively.

A network-adaptive SVC Streaming Architecture

For video streaming, we must consider terminal and network characteristics. The scalable video coding (SVC) can represent video bitstreams in different scalable layers for flexible adaptation to terminal and network characteristics. The SVC can allow for extraction of appropriate partial bitstreams to meet specific target bitrates and spatial resolutions from an SVC bitstream with several spatial, temporal and quality scalability layers. Moreover, the extraction process is fast, so it is possible to extract the partial video streams online to cope with the delivery networks with changing characteristics such as bandwidth etc. With all the advantages of SVC, we design and implement a network-adaptive SVC streaming system to extract partial SVC bitstreams to meet the required target bitrates and spatial resolutions. We present the implementation of our SVC streaming system with experimental results.

A Low Complexity Mode Decision Method for Spatial Scalability Coding

In this paper, a fast mode decision method for the spatial higher layers (SHLs) in scalable video coding (SVC) is proposed based on coding dependency between two adjacent spatial lower and higher layers. The proposed fast mode decision method detects zero motion and zero transform coefficient blocks in the current spatial layer using the already encoded information of the corresponding blocks from the lower layer. The information for zero motion vectors and zero transform coefficients is used to induce a reduced set of candidate modes in SHLs of SVC, which reduces the computation complexity up to about 75% of the total encoding time while maintaining the coding performance with negligible amounts of degradation in peak signal-to-noise ratio values and bitrates.

An All-Zero Block Detection Scheme for Low-Complexity HEVC Encoders

In this paper, an all-zero block detection scheme is proposed prior to DCT to reduce the encoding complexity for high efficiency video coding (HEVC). Since many coding blocks tend to have all zero coefficients after DCT and quantization, it is worthwhile to detect all-zero-quantized blocks for input residual blocks before DCT so that subsequent transform and quantization can be skipped. Unlike previous coding standards, HEVC adopts large transform sizes such as 16 × 16 and 8 × 8. It becomes more difficult to accurately detect all-zero blocks in HEVC because the large transform blocks contains more variety of content characteristics than smaller ones, thus making it ineffective the existing all-zero block (AZB) detection schemes for large transform blocks in HEVC. In this paper, a novel AZB detection scheme is proposed for the case that Hadamard transform is used as a distortion metric for RDO in HEVC. Statistical upper bounds to be all-zero blocks are derived using the relationship between Walsh Hadamard and DCT transform kernels. Then, a small number of quantized coefficients in a upper left corner of a transform block, which are obtained using the relations between Hadamard transform and DCT, are examined for AZB detection. For 32 × 32 blocks, DC coefficients of 8 × 8 sub-blocks are further examined for AZB detection. The experimental results demonstrate that the proposed scheme detects 87.79% of actual AZBs with 2.87% false alarm rate in average, outperforming the state-of-the-art method. Computational complexity to detect AZB is almost negligible compared to the conventional method.

An Efficient Inter-Prediction Mode Decision Method for Temporal Scalability Coding With Hierarchical B-Picture Structure

Although the temporal scalability coding supported by both H.264/AVC and H.264/SVC provides a good means of adapting bitstream scalability in temporal dimension, it entails heavy computational complexity due to bidirectional motion estimation and compensation for B-pictures in temporal scalability levels. To make it more applicable, this paper introduces a fast inter-prediction mode decision method which is efficiently performed using statistical hypothesis testing. The hypothesis testing is performed on mean and variance of pixels in 16 × 16 and 8 × 8 blocks to decide early termination against further processing for their sub-blocks. Fallback check is employed to compromise the tradeoff between the compression efficiency and encoding time saving. The proposed method exhibits effective performance for early termination in the inter-prediction mode decision, thus leading to a significant reduction of the total encoding time up to average 64.8% with small increments in bit amounts and small degradation in visual quality.

A CU-Level Rate and Distortion Estimation Scheme for RDO of Hardware-Friendly HEVC Encoders Using Low-Complexity Integer DCTs

In this paper, a low complexity coding unit (CU)-level rate and distortion estimation scheme is proposed for High Efficiency Video Coding (HEVC) hardware-friendly implementation where a Walsh–Hadamard transform (WHT)-based low-complexity integer discrete cosine transform (DCT) is employed for distortion estimation. Since HEVC adopts quadtree structures of coding blocks with hierarchical coding depths, it becomes more difficult to estimate accurate rate and distortion values without actually performing transform, quantization, inverse transform, de-quantization, and entropy coding. Furthermore, DCT for rate-distortion optimization (RDO) is computationally high, because it requires a number of multiplication and addition operations for various transform block sizes of 4-, 8-, 16-, and 32-orders and requires recursive computations to decide the optimal depths of CU or transform unit. Therefore, full RDO-based encoding is highly complex, especially for low-power implementation of HEVC encoders. In this paper, a rate and distortion estimation scheme is proposed in CU levels based on a low-complexity integer DCT that can be computed in terms of WHT whose coefficients are produced in prediction stages. For rate and distortion estimation in CU levels, two orthogonal matrices of

A hierarchical variable-sized block transform coding scheme for coding efficiency improvement on H.264/AVC

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