Trends in Block-matching Motion Estimation Algorithms

Introduction The primary design objective in video compression is to minimize the average number of bits used to represent a video-sequence in digital form while maintaining sufficient video quality. The high degree of redundancy that exists between successive frames of video sequences makes it possible to achieve high compression ratios. In order to exploit the spatial and temporal redundancy in an image sequence, a number of techniques have been developed to minimize the amount of information required to faithfully reproduce the image sequence at the decoder. A high compression ratio is achieved using a lossy step at the expense of image quality. Video compression techniques rely on three principles: the reduction of spatial, temporal and statistical redundancies. Coding techniques which reduce the spatial correlation are referred to as intraframe coding, whereas those which tackle the temporal correlation are called interframe techniques. All these techniques are base of the video-encoder in MPEG-2 standard. It is no the newest compression standard, but today is the most fitting on in many applications. The choice to use MPEG-2 in DVD-video and DVB-S, C, T standards yielded in its popularity. The secret of the success rests in well chosen balance between computational complexity and compression ratio. Thank to the ISO standard formulation, where is only syntax specified, it is possible to enhance the encoding efficiency with use of new motion estimation algorithms. One way to enhance the compression ratio is to enlarge the GOP sequence by putting in more B-frames. It requires involving the motion estimation algorithm with accuracy as good as possible. The purpose of this paper is to lead reader through today's motion estimation algorithms.