Hexagonal Search Research Articles

A Novel 3-D Predict Hexagon Search Algorithm for Fast Block Motion Estimation on H.264 Video Coding

In the upcoming video coding standard MPEG-4 AVC/JVT/H.264, motion estimation is allowed to use multiple references and multiple block sizes to improve the rate-distortion performance. However, full exhaustive search of all block sizes is computational intensive with complexity increasing linearly to the number of allowed reference frames and block sizes. In block motion estimation, a search pattern with a different shape or size has a very important impact on search speed and distortion performance. Based on an in-depth examination for the influence of search pattern on speed performance, a novel search algorithm, three-dimensional predict hexagon search (3DPHS), is proposed in this paper. The 3DPHS depends on the characteristics of motion vector distribution; it can predict the object movement in horizontal and vertical direction with a novel search pattern. The proposed algorithm also considers the characteristics of multiple reference frames and multiple block sizes in H.264. The analysis results show that the speed improvement of 3DPHS over some popular fast search algorithms is about 25%-75%. The compression quality is almost the same compared with Full Search

A fast block-matching algorithm based on variable shape search

Block-matching motion estimation plays an important role in video coding. The simple and efficient fast block-matching algorithm using Variable Shape Search (VSS) proposed in this paper is based on diamond search and hexagon search. The initial big diamond search is designed to fit the directional centre-biased characteristics of the real-world video sequence, and the directional hexagon search is designed to identify a small region where the best motion vector is expected to locate. Finally, the small diamond search is used to select the best motion vector in the located small region. Experimental results showed that the proposed VSS algorithm can significantly reduce the computational complexity, and provide competitive computational speedup with similar distortion performance as compared with the popular Diamond-based Search (DS) algorithm in the MPEG-4 Simple Profile.

Novel cross-diamond-hexagonal search algorithms for fast block motion estimation

We propose two cross-diamond-hexagonal search (CDHS) algorithms, which differ from each other by their sizes of hexagonal search patterns. These algorithms basically employ two cross-shaped search patterns consecutively in the very beginning steps and switch using diamond-shaped patterns. To further reduce the checking points, two pairs of hexagonal search patterns are proposed in conjunction with candidates found located at diamond corners. Experimental results show that the proposed CDHSs perform faster than the diamond search (DS) by about 144% and the cross-diamond search (CDS) by about 73%, whereas similar prediction quality is still maintained.

Enhanced Hexagonal Search for Fast Block Motion Estimation

Fast block motion estimation normally consists of low-resolution coarse search and the following fine-resolution inner search. Most motion estimation algorithms developed attempt to speed up the coarse search without considering accelerating the focused inner search. On top of the hexagonal search method recently developed, an enhanced hexagonal search algorithm is proposed to further improve the performance in terms of reducing number of search points and distortion, where a novel fast inner search is employed by exploiting the distortion information of the evaluated points. Our experimental results substantially justify the merits of the proposed algorithm.

Adaptive dual-cross search algorithm for block-matching motion estimation

In this paper, we present two new and efficient block-matching algorithm (BMAs) for fast motion estimation used in motion-compensated video compression. The proposed algorithms are improvement of existing BMAs and consist of three effective steps: 1) Initial search center prediction, 2) early search termination, and 3) dual-cross pattern search. Extensive simulation results and comparative analysis have shown that the proposed algorithms outperform conventional algorithms, like the three-step search, orthogonal search and diamond search, as well as the newly proposed algorithms, like the hexagonal search and adaptive rood pattern search, in terms of both video peak signal-to-noise ratio and the number of checking points are evaluated.

Hierarchical motion estimation with content-based meshes

Two-dimensional mesh-based models provide a good alternative to motion estimation and compensation. The estimation of the best node-point motion vectors is a challenging task. To this effect, Nakaya and Harashima (1994) proposed a hexagonal matching procedure. Toklu et al. improved the hexagonal search algorithm in terms of both motion-estimation accuracy and computational complexity by employing a hierarchy of regular meshes. Recognizing the limitations of regular meshes, Van Beek et al. (1997) extended Toklu et al.'s (1996) work by utilizing content-based meshes. Here, we provide an alternative hierarchical motion-estimation method with content-based meshes where hierarchical representations are employed for both the images and the irregular meshes in order to provide further improvements in computational complexity as well as motion accuracy. The comparison results are provided with real video sequences.