Rate-distortion Optimized Mode Decision Research Articles

Content Adaptive Lagrange Multiplier Selection for Rate-Distortion Optimization in 3-D Wavelet-Based Scalable Video Coding.

Rate-distortion optimization (RDO) plays an essential role in substantially enhancing the coding efficiency. Currently, rate-distortion optimized mode decision is widely used in scalable video coding (SVC). Among all the possible coding modes, it aims to select the one which has the best trade-off between bitrate and compression distortion. Specifically, this tradeoff is tuned through the choice of the Lagrange multiplier. Despite the prevalence of conventional method for Lagrange multiplier selection in hybrid video coding, the underlying formulation is not applicable to 3-D wavelet-based SVC where the explicit values of the quantization step are not available, with on consideration of the content features of input signal. In this paper, an efficient content adaptive Lagrange multiplier selection algorithm is proposed in the context of RDO for 3-D wavelet-based SVC targeting quality scalability. Our contributions are two-fold. First, we introduce a novel weighting method, which takes account of the mutual information, gradient per pixel, and texture homogeneity to measure the temporal subband characteristics after applying the motion-compensated temporal filtering (MCTF) technique. Second, based on the proposed subband weighting factor model, we derive the optimal Lagrange multiplier. Experimental results demonstrate that the proposed algorithm enables more satisfactory video quality with negligible additional computational complexity.

Allowable depth distortion based fast mode decision and reference frame selection for 3D depth coding

To improve the coding efficiency and meanwhile reduce the complexity of the depth video encoder in 3D system, we present an efficient depth coding scheme based on the allowable depth distortion (ADD) in view synthesis. Firstly, we analyze the depth distortion in view synthesis and present a new ADD-based Rate Distortion (RD) optimization cost function to improve the mode/reference decision criteria. Then, we present an early mode and reference frame selection algorithm, which skips the unnecessary and complex mode and reference frame when the depth distortion is within the ADD interval. Meanwhile, the coding efficiency is improved by RD optimized mode decision and reference frame selection. The experimental results show that the proposed overall algorithm, which integrates the fast mode decision, reference frame selection and RD optimization, can reduce the depth coding complexity from 32.47 to 72.59, and 55.95 % on average over different test sequences. Meanwhile, the proposed algorithm achieves 1.34 and 1.58 dB average Bjontegaard Delta peak signal-to-noise ratio gain in terms of the view synthesis quality at low and high bit rate, respectively. In terms of the bit rate reduction, it reduces 54.66 and 49.60 % Bjontegaard Delta bit rate on average at low and high bit rate, respectively, while maintaining the same view synthesis image quality.

Enhanced SATD-based cost function for mode selection of H.264/AVC intra coding

In H.264/AVC, the concept of rate-distortion optimization (RDO) mode decision has proven to be an important coding tool. However, this mode decision method makes the encoding process extremely complex, especially in the computation of the rate-distortion cost function, which includes the computations of the sum of squared difference (SSD) between the original and reconstructed image blocks and context-based entropy coding of the block. In this paper, we propose an enhanced low-complexity cost function for H.264/AVC intra 4 × 4 and 8 × 8 mode selections. The enhanced cost function uses sum of absolute Hadamard-transformed differences (SATD) and mean absolute deviation of the residual block to estimate distortion part of the cost function. A threshold-based large coefficients count is also used for estimating the bit-rate part. The proposed method improves the rate-distortion performance of conventional fast cost functions while maintaining low complexity requirement. As a result, the encoding process can be significantly accelerated with the use of the proposed cost function. Simulation results confirm that the proposed method reduces about 83.74 % computation of intra encoding of JM 12.4 encoder with negligible rate-distortion performance degradation.

General Architecture for MPEG-2/H.263/H.264/AVC to H.264/AVC Intra Frame Transcoding

The latest international video-coding standard H.264/AVC significantly achieves better coding performance compared to prior video coding standards such as MPEG-2 and H.263, which have been widely used in today's digital video applications. To provide the interoperability between different coding standards, this paper proposes an efficient architecture for MPEG-2/H.263/H.264/AVC to H.264/AVC intra frame transcoding, using the original information such as discrete cosine transform (DCT) coefficients and coded mode type. Low-frequency components of DCT coefficients and a novel rate distortion cost function are used to select a set of candidate modes for rate distortion optimization (RDO) decision. For H.263 and H.264/AVC, a mode refinement scheme is utilized to eliminate unlikely modes before RDO mode decision, based on coded mode information. The experimental results, conducted on JM12.2 with fast C8MB mode decision, reveal that average 58%, 59% and 60% of computation (re-encoding) time can be saved for MPEG-2, H.263, H.264/AVC to H.264/AVC intra frame transcodings respectively, while preserving good coding performance when compared with complex cascaded pixel domain transcoding (CCPDT); or average 88% (a speed up factor of 8) when compared with CCPDT without considering fast C8MB. The proposed algorithm for H.264/AVC homogeneous transcoding is also compared to the simple cascaded pixel domain transcoding (with original mode reuse). The results of this comparison indicate that the proposed algorithm significantly outperforms the mode reuse algorithm in coding performance, with only slightly higher computation.

Efficient Algorithm for H.264/AVC Intra Frame Video Coding

This letter proposes an enhanced sum of absolute transform differences (SATD)-based intra mode decision for H.264/advanced video coding intra frame coding, which is accomplished in two stages. In the first stage, the low-frequency AC components of discrete cosine transform block of a MB is used to select I4 MB or I16 MB mode prediction; while in the second stage SATD coefficients, including SATD value and its variance, is used to skip improper modes for rate-distortion optimization mode decision. This letter compares the proposed algorithm performance with other distinct algorithms such as image structure tensor and dominant edge direction, and so on, and the results indicate that the proposed algorithm significantly outperforms these algorithms, in both rate-distortion performance and computation performance.

Algorithm analysis and architecture design for rate distortion optimized mode decision in high definition AVS video encoder

There are abundant intra and inter prediction modes in the AVS video coding standard. Rate distortion optimized mode decision can fully utilize this flexibility to improve the spatio-temporal prediction efficiency and maximize the coding efficiency. However, the implementation complexity is dramatically high due to huge throughput burden. Hardware oriented mode decision algorithm is tailored for VLSI implementation in this work for high definition video coding. Mode preselection is employed to alleviate the dramatic throughout burden. Also, intelligent pipeline scheduling mechanism is proposed to break the intrinsic data dependency in intra prediction, which is directly related with mode decision. The proposed simplified algorithm is well-suited for hardware implementation with small performance penalty. Finally, the VLSI architecture is proposed with good trade off between circuit consumption and rate distortion performance.

SATD-Based Intra Mode Decision for H.264/AVC Video Coding

In this letter, a rate estimation technique using transform coefficient variance is proposed in the rate-distortion cost function for intra mode decision. The new cost function achieves better coding performance than the cost function using the ¿-domain model. The new cost function brings out an average speed-up factor of 13 when compared with the rate-distortion optimization (RDO) mode decision, but with considerable degradation in rate-distortion performance. To improve the coding performance, we propose a sum of the absolute transformed differences (SATD)-based mode decision algorithm, which incorporates both SATD and the variance information into the RDO mode decision method. The results show that the SATD-based mode decision scheme can achieve a significant improvement in computation (with 21% of total encoding time, or a speed-up factor of 5) with negligible peak signal-to-noise ratio loss. The proposed algorithm is also compared with two other distinct algorithms , and the results indicate that the proposed algorithm outperforms these two edge detection algorithms in coding performance, as well as time saving.

A New Low-Complexity Integer Distortion Estimation Method for H.264/AVC Encoder

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, a new low-complexity distortion estimation method for the H.264 rate-distortion optimized mode decision is proposed. Coding processes, such as discrete cosine transform (DCT), quantization, inverse quantization, inverse DCT, and reconstruction, are needed to compute the distortion in an H.264 encoder. To reduce these computations, we estimate the distortion using coefficients calculated in the quantization process and eliminate the inverse quantization, inverse DCT, and reconstruction processes. In the proposed method, the distortion is computed by integer operations, which is more efficient for the hardware implementation. The simulation results show that the proposed method can reduce the encoding time by about 10% with negligible degradation in the coding performance. </para>

Cascaded mode decision for MPEG-2 to H.264/AVC intra frame transcoding

The newest international video-coding standard H.264/AVC significantly achieves better coding performance compared to prior video coding standards such as MPEG-2, which has been widely used in today's digital video applications. To provide the interoperability between MPEG-2 and H.264/AVC, in this paper we propose an efficient cascaded mode decision for MPEG-2 to H.264/AVC intra frame transcoding, which is accomplished in two stages. In the first stage, the low-frequency AC components of discrete cosine transform (DCT) block of a MB is used to select I4MB or I16MB mode prediction; while in the second stage sum of absolute Hadamard transform differences (SATD) coefficients, including SATD value and its variance, is used to skip improper modes for rate distortion optimization (RDO) mode decision. The experimental results, conducted on JM12.2 with fast C8MB mode decision, reveal that over 49% of computation time on average can be saved, while preserving good coding performance when compared with complex cascaded pixel domain transcoding (CCPDT); or 85% (a speed up factor of 7) when compared with CCPDT without considering fast C8MB. The coding performance is also compared with two other distinct algorithms, and the results demonstrate that the proposed algorithm momentously outperforms these two algorithms in all three respects (PSNR), bit rate as well as computation time.

Error Resilient Coding and Error Concealment in Scalable Video Coding

Scalable video coding (SVC), which is the scalable extension of the H.264/AVC standard, was developed by the Joint Video Team (JVT) of ISO/IEC MPEG (Moving Picture Experts Group) and ITU-T VCEG (Video Coding Experts Group). SVC is designed to provide adaptation capability for heterogeneous network structures and different receiving devices with the help of temporal, spatial, and quality scalabilities. It is challenging to achieve graceful quality degradation in an error-prone environment, since channel errors can drastically deteriorate the quality of the video. Error resilient coding and error concealment techniques have been introduced into SVC to reduce the quality degradation impact of transmission errors. Some of the techniques are inherited from or applicable also to H.264/AVC, while some of them take advantage of the SVC coding structure and coding tools. In this paper, the error resilient coding and error concealment tools in SVC are first reviewed. Then, several important tools such as loss-aware rate-distortion optimized macroblock mode decision algorithm and error concealment methods in SVC are discussed and experimental results are provided to show the benefits from them. The results demonstrate that PSNR gains can be achieved for the conventional inter prediction (IPPP) coding structure or the hierarchical bi-predictive (B) picture coding structure with large group of pictures size, for all the tested sequences and under various combinations of packet loss rates, compared with the basic joint scalable video model (JSVM) design applying no error resilient tools at the encoder and only picture copy error concealment method at the decoder.

SKIP Prediction for Fast Rate Distortion Optimization in H.264

In H.264, the optimal coding mode for each macroblock (MB) is selected by exhaustively searching all MB modes in the multiple reference frames. The exhaustive mode search has a very high computational complexity. This paper proposes three different approaches along with their combination to reduce the complexity of the rate-distortion optimized mode decision process in H.264. These approaches are based on transform-domain properties and spatio-temporal correlation in video sequences. Experimental results demonstrate that the proposed methods achieve around 5-7 times improvement in average speedup with good prediction quality and comparable bitrate.

Efficient MPEG-2 to H.264/AVC Transcoding of Intra-Coded Video

This paper presents an efficient transform-domain architecture and corresponding mode decision algorithms for transcoding intra-coded video from MPEG-2 to H.264/AVC. Low complexity is achieved in several ways. First, our architecture employs direct conversion of the transform coefficients, which eliminates the need for the inverse discrete cosine transform (DCT) and forward H.264/AVC transform. Then, within this transform-domain architecture, we perform macroblock-based mode decisions based on H.264/AVC transform coefficients, which is possible using a novel method of calculating distortion in the transform domain. The proposed method for distortion calculation could be used to make rate-distortion optimized mode decisions with lower complexity. Compared to the pixel-domain architecture with rate-distortion optimized mode decision, simulation results show that there is a negligible loss in quality incurred by the direct conversion of transform coefficients and the proposed transform-domain mode decision algorithms, while complexity is significantly reduced. To further reduce the complexity, we also propose two fast mode decision algorithms. The first algorithm ranks modes based on a simple cost function in the transform domain, then computes the rate-distortion optimal mode from a reduced set of ranked modes. The second algorithm exploits temporal correlations in the mode decision between temporally adjacent frames. Simulation results show that these algorithms provide additional computational savings over the proposed transform-domain architecture while maintaining virtually the same coding efficiency.

Fast H.264 Intra-prediction mode selection using joint spatial and transform domain features

A fast H.264 Intra-prediction mode selection scheme is proposed in this work. The objective is to reduce the encoder complexity without significant rate–distortion performance degradation. The proposed method uses spatial and transform domain features of the target block jointly to filter out the majority of candidate modes. This is justified by examining the posterior error probability and the average rate–distortion loss. For the final mode selection, either the feature-based or the RDO (rate–distortion optimization)-based method is applied to 2–3 candidate modes. It is demonstrated by experimental results that the proposed scheme demands only 7–10% of the complexity of the RDO (rate–distortion optimized) mode decision scheme with little quality degradation.