An-Chao Tsai

Intensity Gradient Technique for Efficient Intra-Prediction in H.264/AVC

This study presents an intensity gradient approach for intra-prediction in H.264 encoding system, which enhances the performance and efficiency of previous fast algorithms. We propose a preprocessing stage in which eight orientation features are extracted from a macro block by the intensity gradient filters. The orientation features are utilized to select a subset of prediction modes to be involved in the rate-distortion calculation so that the encoding time can be reduced. The simulation results indicate that the intensity gradient based algorithm for intra-prediction contributes better tradeoff between rate-distorion performance and encoding complexity than the previous algorithms. Compared to H.264 reference software, the proposed algorithm introduces slight PSNR degradation and bit rate increase but saves around 76% of the total encoding time with all intra-frame coding.

Effective Subblock-Based and Pixel-Based Fast Direction Detections for H.264 Intra Prediction

In H.264/AVC intra-frame coding, the rate-distortion optimization (RDO) is employed to select the optimal coding mode to achieve the minimum rate-distortion cost. Due to a large number of combinations of coding modes, the computational burden becomes extremely high in intra-prediction. In this paper, we propose two fast, efficient but reliable direction detection algorithms by computing subblock and pixel direction differences. Both proposed methods effectively estimate the edge direction inside the block to narrow down the predictive modes to reduce the RDO computation. Experimental results show that the proposed methods can reduce the encoding time by about 60% with negligible loss of coding performance. For hardware realization, a fast mode decision VLSI circuit for intra-prediction with the silicon core size of 0.12 times 0.12 mm2 at 0.18-mum CMOS technology is implemented. The fast mode decision VLSI in three-stage pipelined architecture operated at 173 MHz can encode 30 fps real-time videos up to Level 5.

A novel fast algorithm for intra mode decision in H.264/AVC encoders

This paper presents a fast mode decision algorithm for H.264 intra prediction based on dominant edge strength (DES). In H.264 intra prediction, the computation-extensive rate distortion optimization (RDO) technique with full intra mode search is used to select the best mode for each macroblock. To reduce the computational load in mode decision, the DES which is corresponding to a decision mode is detected first. In accordance with the detected dominant edge, a subset of the prediction modes is then chosen for RDO calculation. The proposed algorithm only searches 4 modes instead of 9 for the 4times4 luma blocks. As for the 16times16 or 8times8 chroma blocks, instead of 4 modes, only 2 modes are required to be searched. Experimental results revealed that the computation time of the proposed fast intra prediction algorithm is averagely reduced to 40% of the full search method with slight PSNR degradation

Structuralized context-aware content and scalable resolution support for wireless VoD services

Video-on-demand (VoD) services allow users to receive real-time multimedia contents from afar distance. Yet, current architectures still require a context-aware indexing system to help users learn about story details. In this paper, we present a semantic processing system that offers structuralized video contents based on four basic entities: who, what, where, and when. Thus, users can select clips of interest among a video according to the guided clues. At the same time, we also present an SVC-compatible coding that improves spatial scalability in order to transmit the structuralized results for mobile devices efficiently. Users can, therefore, get a higher PSNR in low bit-rate applications. The experimental results have demonstrated the feasibility and effectiveness of our proposed system.

A Simple and Robust Direction Detection Algorithm for Fast H.264 Intra Prediction

In H.264/AVC intra frame coding, the rate-distortion optimization is employed to select the optimal coding mode to achieve the minimum rate-distortion cost. Due to a large number of combinations of coding modes, the computational burden becomes extremely high in intra prediction, hi this paper, we propose a fast, efficient but reliable vector based detection algorithm for H.264 intra frame coding system. The proposed algorithm effectively estimates the edge direction inside the block to narrow down the predictive modes to reduce the RDO calculations. Experimental results show that the proposed method can reduce the encoding time by about 60% with negligible coding loss.

Classified Multifilter Up-Sampling Algorithm in Spatial Scalability for H.264/SVC Encoder

H.264/scalable video coding (SVC) has spatial scalability which can provide various resolution sequences for a single encoded bit-stream. The various resolutions can be achieved by up-sampling a lower image resolution sequence. The up-sampling method employed in H.264/SVC is directly proportional to the video quality. In order to improve the video quality with an effective up-sampling method, we propose a classified multifilter up-sampling algorithm for H.264/SVC in spatial scalability which classifies an image region as edges and nonedges. An appropriate filter is then applied to up-sample the image. In the proposed scheme, we applied the Wiener filter for edges and conventional filter for nonedges within the defined window size to preserve the edges in the up-sampled image sequence. The experimental results show that the average peak signal-to-noise ratio improvement and bit-rate reduction are 0.5 dB and 9%, respectively, which confirm that the performance of the proposed method is better than that of the existing H.264/SVC standard.

Efficient Intra Prediction in H.264 Based on Intensity Gradient Approach

This study presents an intensity gradient approach to intra prediction in H.264 encoding system, which enhances the performance and efficiency by means of edge orientation of the gradient filter. We propose a pre-processing stage in which eight-orientation feature are extracted from a macro block that selects four modes to be applied to the block among a set of predefined modes. It is shown that by choosing number of modes used in rate-distortion calculation lead to significant enhancement in the performance of intra prediction. The validity of this algorithm is confirmed experimentally. The simulation results indicate that the intensity gradient-based algorithm for intra prediction contributes to the bit-rate reduction compared to that of previous algorithms and saves around 53% of the total encoding time in H.264.

Effective Search Point Reduction Algorithm and its VLSI Design for HDTV H.264/AVC Variable Block Size Motion Estimation

Variable block size motion estimation (VBSME) in H.264/AVC has greatly led to achieve an optimal inter frame encoding. However, the computation burden of the VBSME becomes the bottleneck of the H.264/AVC encoders. The conventional architecture in hardware realization is hard to adopt a fast software algorithm suitable to reduce the VBSME computation burden. Therefore, this paper presents a search point reduction (SPR) algorithm with an efficient hardware design, able to decrease the motion estimation time while maintaining the coding performance of H.264. The effectiveness of the proposed method is compared with those of existing methods with respect to chip area, operation frequency, and throughput rate. The proposed SPR algorithm increases the coding speed by around 90%; with a peak signal-to-noise ratio drop of less than 0.1 dB than that achieved by the JM reference software. The proposed SPR algorithm can operate at 200 MHz with 191 k gate count, which supports high-definition television 1280  720 format.

Projection Based Adaptive Window Size Selection for Efficient Motion Estimation in H.264/AVC

This paper introduces a block based motion estimation algorithm based on projection with adaptive window size selection. The blocks cannot match well if their corresponding 1D projection does not match well, with this as foundation 2D block matching problem is translated to a simpler 1D matching, which eliminates majority of potential pixel participation. This projection method is combined with adaptive window size selection in which, appropriate search window for each block is determined on the basis of motion vectors and prediction errors obtained for the previous block, which makes this novel method several times faster than exhaustive search with negligible performance degradation. Encoding QCIF size video by the proposed method results in reduction of computational complexity of motion estimation by roughly 45% and over all encoding by 23%, while maintaining image/video quality.

A simple direction detection algorithm for Fast H.264 intra prediction

The rate distortion optimization technique suggested in H.264/AVC searches the best coding mode consumed extremely high computation complexity in intra and inter predictions due to full mode search. This paper presents a fast direction detection algorithm to effectively reduce the number of the possible candidate modes for H.264 intra prediction. The proposed fast algorithm is based on the direction detection of the edge inside the block. Instead of full intra mode search, the proposed method only searches 4 modes for 4times4 luminance blocks, and 2 modes for 16times16 luminance and 8times8 chrominance blocks. Experimental results reveal that the proposed algorithm significantly reduces the encoding time over 60% in average with slight loss in bit-rate and PSNR.