| 2D video is incomparable with stereo video, which could provide viewers depth sense according to stereo disparity theory. By prevailing of stereo video, enormous of video data need to be stored and transmitted, especially in real-time system, high resolution and multi points-points communications. Recently, 2D encoding theory and technology were already maturity, but not in stereo video and multi points. How to compressing stereo video data became a hotspot in communication and it has also important for application of stereo video. Nowadays, stereo video compression has been paid attention by many researchers.DISTIMA project was an integrated stereo video communication system, which was based on MPEG-2 coding standard and developed by Germany, France and some other European nations. ATTEST proposed a novel stereo video compression that was based on a more flexible joint transmission of monoscopic color video and associated per-pixel depth information. From this 3D data representation format, one or more"virtual"views of a 3D scene can then be synthesized in real-time at the receiver side by means of so-called depth-image-based rendering (DIBR) techniques. International standard organization MPEG built a stereo video coding special team, which mainly discussed stereo video requirements and techniques in apply, and for purpused of a uniform stereo video standard. There were two stereo video schemes in all, which was depth based image rendering, and another one was block-based estimation with residual compensation.This paper mainly researched on stereo video coding in 3DTV system, and a pair of rectified images with small baseline were as input. Three stereo video compression algorithms were proposed and organized as follows.1. More exactly disparity estimation could get smaller compression stream and finer quality of reconstructed image by depth based image rendering. Loop belief propagation could get exactly matching by minimizing global energy, but it would take heavy computational cost. This paper proposed a temporal correlation based belief propagation (BP) stereo video coding, which was based on BP's message passing provides a time-varying adaptive support region for stereo matching to deal with textureless regions and depth discontinuities elegantly. In textureless regions, for example, the influence of a message can be passed far away. On the other hand, the influence in discontinuous regions will fall off quickly. Stereo video were organized in group. Disparity of every I stereo pair was calculated by standard loop BP, and disparity of every P stereo pair was computed selectively by difference of temporal frames. Finally, reference video and disparity sequences were encoded.2. If algorithms of disparity estimation were not referred objects, there will be large residual around object edges. And then this would be effected subjective quality of reconstructed image. So this paper proposed a disparity estimation algorithm based on objects.Firstly, mainly edges of object were extracted by Canny, then feature points were detected by Harris, and original matching relation was constructed, finally outlier disparities were deleted by fundamental matrix estimation processing. And a sparse disparity map was constructed, and then disparity in object needed to be calculated.It is a difficult problem for selecting unit for calculating disparity of object. It will be too dispersed to be calculated by pixel-based and it is also difficult for selecting size of block by block-based. Because of disparity discontinuous always occurs with large changes in intensity, this paper proposed every column of image was adaptable divided into non-overlapping segments by continuous constraint of intensity in vertical, and every segment was considered as a unit for matching. And then size of searching windows was referenced by disparity of left and right adjacent object edges. Finally, reference and disparity sequences were encoded.3. Due to view points, intensity source, and noise effect, some information could not be reconstructed by depth base image rendering, but they could be remedied by residual compensation. This paper proposed a content-based four dimensional (4D) matrix stereo video algorithm. Differ from typical block-based method, this motion estimation was calculated by reference frames, which would reduce almost estimation computation. And then redundant of temporal, spatial and disparity correlation was reduced by 4D matrix DCT. Coefficients after transforming were assembled in low frequency and temporal, and then correlation between coefficients could be enhanced by 4D matrix Z scan, which was fitable for variable length coding.Several stereo video and image were tested, and experimental results were compared between these methods.In contrast of standard loop BP algorithm, temporal correlation based BP stereo video coding algorithm could reduce 83.8% computation time under the same reconstructed image quality. So it was an efficient disparity sequence algorithm for stereo video transmitting and free view point rendering. Experiment results showed that this algorithm could preserve details well, but some errors occured in edge of object. This might affect stereo sense because it could not be remedied in further by lacking residual compensation process.Object and continuous constraint of intensity based stereo video coding could reserve well in edges and details, but not in discontinuous intensity. Object edges could be reconstructed more integrity by this method than temporal correlation based BP stereo video coding.Stereo video could be reconstructed well by 4D matrix based stereo video coding. With accretion of bit rate, the quality of reconstructed image could get higher. By compared with the other two algorithm proposed in this paper, 4D matrix based stereo video coding may be blockness in textureless region at lower bit rate, but it has higher fidelity, which reserved original image information well and may be helpful for reconstructed stereo sense.Experiment results showed that it would be finer quality of reconstructed image by depth based image rendering for simple content stereo video or image. But for complexity content stereo video, residual compensation could resolve errors by occlusion and exposure well.
|
PDF Full Text Request