Lap-Pui Chau

A novel hexagon-based search algorithm for fast block motion estimation

In block motion estimation, search patterns with different shape or size have a very important impact on search speed and distortion performance. In this paper, we propose a novel algorithm using a hexagon-based search (HEXBS) pattern for fast block motion estimation. The proposed HEXBS algorithm may find any motion vector with fewer search points than the diamond search (DS) algorithm. The speedup gain of the HEXBS method over the DS algorithm is more striking for finding large motion vectors. Experimental results substantially justify the fastest performance of the HEXBS algorithm compared with several other popular fast algorithms.

A temporal error concealment algorithm for H.264 using Lagrange interpolation

In this paper, we propose an efficient temporal error concealment algorithm for the new coding standard H.264, which makes use of the Lagrange interpolation formula. In H.264, a 16/spl times/16 inter macroblock can be divided into different block shapes for motion estimation, and each block has its own motion vector. For nature video, the motion vectors within a small area are correlative. Since the motion vector in H.264 covers a smaller area than previous coding standards, the correlation between neighboring motion vectors increases. We can use the Lagrange interpolation formula to constitute a polynomial that describes the motion tendency of motion vectors, which are next to the lost motion vector, and use this polynomial to recover the lost motion vector. The simulation result shows that our algorithm can efficiently improve the visual quality of corrupted videos.

Fast mode decision for spatial scalable video coding

Scalable video coding (SVC) is an on-going standard and the current working draft (WD) is an extension of H.264/AVC. It provides scalability at the bit stream level with good compression efficiency, and allowing free combinations of spatial, temporal and SNR scalability. In the WD, exhaustive search technique is employed to select the best coding mode for each macroblock. This technique achieves highest possible coding efficiency, but it results in higher computational complexity. To overcome this, we propose a novel fast mode decision scheme for spatial scalability in SVC. In this scheme, the mode distribution relationship between base layer and enhancement layers is employed to reduce the candidate mode set at enhancement layers. The experimental results show that the proposed scheme provides significant reduction in computational complexity without any noticeable coding loss

A novel intra-rate estimation method for H.264 rate control

In this paper, we present a novel intra-rate estimation method for H.264 rate control. The proposed method establishes the intra-frame rate-quantization (R-Q) estimation model by using gradient-based picture complexity measure. The proposed model aims at selecting accurate quantization parameters for intra-coded frames which can fully comply with buffer constraints. By adaptively updating this R-Q model, the performance of the model can be guaranteed regardless of the changing of video frame characteristics. Simulation results show that by using our proposed scheme, better rate control for intra-frames and frames at scene changes can be achieved. As a result, the number of skipped frames is significantly reduced thus it provides improved visual quality of the reconstructed pictures

A novel unequal error protection approach for error resilient video transmission

We address the problem of unequal error protection (UEP) for MPEG-2/H.263 video over a wireless packet-erasure channel. Unequal amounts of protection are allocated to the different frames of a group-of-pictures (GOP) to provide a graceful degradation of video quality as packet loss rate varies. We use a genetic algorithm (GA) to get the allocation pattern quickly. Theoretical analysis and experimental results both demonstrate the advantages of the proposed algorithm.

An efficient inter mode decision approach for H.264 video coding

Variable size block motion estimation is a very important technique for video coding. The new H.264 standard employs 7 different size block types which can significantly improve the coding performance compared with the previous video coding standards. On the other hand, the computational complexity of H.264 encoder increases dramatically due to the various coding modes used. In this paper, an efficient inter mode decision approach is presented. The objective is to reduce the number of candidate block types in the motion estimation while maintaining the coding efficiency. Experimental results show that the proposed method can save the computation cost by up to 42% at the same PSNR and bitrate

Blind Super-Resolution Image Reconstruction using a Maximum a Posteriori Estimation

This paper proposes a new algorithm to address blind image super-resolution by fusing multiple blurred low-resolution (LR) images to render a high-resolution (HR) image. Conventional super-resolution (SR) image reconstruction algorithms assume either the blurring during the image formation process is negligible or the blurring function is known a priori. This assumption, however, is impractical as it is difficult to eliminate blurring completely in some applications or characterize the blurring function fully. In view of this, we present a new maximum a posteriori (MAP) estimation framework that performs joint blur identification and HR image reconstruction. An iterative scheme based on alternating minimization is developed to estimate the blur and HR image progressively. A blur prior that incorporates the soft parametric blur information and smoothness constraint is introduced in the proposed method. Experimental results show that the new method is effective in performing blind SR image reconstruction where there is limited information about the blurring function.

An enhanced hexagonal search algorithm for block motion estimation

Based on the hexagonal search method recently developed, an enhanced hexagonal search algorithm is proposed to further improve the performance in terms of reducing the number of search points and distortion, where a simple prediction scheme and a novel fast inner search are employed. Our experimental results show that the enhanced hexagonal search algorithm substantially outperforms the original one in terms of number of search points and distortion.

Efficient three-step search algorithm for block motion estimation in video coding

The three-step search algorithm has been widely used in block matching motion estimation due to its simplicity and effectiveness. The sparsely distributed checking points pattern in the first step is very suitable for searching large motion. However, for quasi-stationary blocks it will easily lead the search to be trapped into a local minimum. In this paper we propose a modification on the three-step search algorithm which employs a small diamond pattern in the first step, and the unrestricted search step is used to search the center area. Experimental results show that the proposed algorithm performs better than new three-step search in terms of MSE and requires less computation by up to 15% on average.

Frame-skipping transcoding with motion change consideration

Transcoding is adopted to deliver video content to a broad range of end users with different preferences and bandwidth constraints. Frame-skipping transcoding is one of the solutions to reduce the temporal resolution of the video sequence and decrease the overall bit rate. Traditionally used control scheme in frame-skipping transcoding is based on buffer constraint or considers the motion activity of each frame. In this paper, we would like to propose a new frame-skipping control scheme that considers the motion change and tries to reduce the jerky effects caused by the undesired frame skipping. Experiments show that proposed frame-skipping control scheme can produce transcoded video look more like the original one and hence remain the visual quality.