| Rapid developments of virtual reality technology have greatly enriched the audiovisual experience of people in recent years.As one of the main construction technologies of virtual scenes,panoramic videos are widely used in many applications and have attracted the attention of both industry and academia.Compared with traditional videos,the property of high immersion of panoramic videos bring the users better experience.However,they also bring great challenges to the bandwidth of network and storage.Furthermore,all of the current video coding standards cannot be directly applied to panoramic videos.Generally,before processing panoramic videos,they need to be projected in the plane.This thesis aims at the projection of panoramic videos,and proposes a spheical distance Lanczos(SDL)interpolation algorithm and an Equirectangular and Adjusted Cubemap Projection(ERACP)format that can freely divides the sphere according to the parallels,which can improve the performance of encoding of panoramic videos.Aiming at the problems of selecting the inappropriate reference pixels and calculating the inaccurate weights for interpolation using the distances measured in the plane rather than the original distances measured on the sphere in Lanczos interpolation algorithm in the process of projection format conversions,many researches have been worked in this thesis.Concretely,the inappropriation of selecting the reference pixels and the inaccuration of calculating the weights for interpolation in Lanczos interpolation algorithm in the process of projection format conversions are detailed.Then SDL interpolation algorithm is proposed in this thesis selecting the reference pixels and calculating the weights for interpolation reasonably according to the original correlation among the pixels on the sphere.The characteristics of the deformation of the specific projection format is also considerd in the proposed algorithm.Experimental results have demonstrated that proposed SDL interpolation algorithm can achieve an increase of PSNR by 3.52 d B on average for Y,by 1.85 d B on average for U,by 1.82 d B on average for U in the process of projection format conversion between ERP and CPP.For the other projection format conversions,such as the conversion between ERP and CMP,the conversion between ERP and ACP,the performance of proposed SDL algorithm is still better than that of Lanczos interpolation algorithm.Aimming at the projection format,many reasearches have been worked in this thesis and the characteristics of ERP format and ACP format in different areas on the sphere are detailed through experiments.Based on the comprehensive consideration of spherical uniform sampling and the continuity of texure in the planar perspective frames after projection,a ERACP projection format is proposed in this thesis by separating the sphere by 45 degree parallel and using different projection formats for different areas on the sphere.Our proposed projection format has a certain coding performance gain compared with that of ERP format through experiments.Finally,the proposed projection format is improved for adapting more general applications.A ERACP projection format that can freely divides the sphere is proposed and the research method on the optimal segmentation is given.Accoding to the uniform distribution of sampling points in the planar perspective frames,the range of the optimal segmentation on the sphere is deduced theoretically.Combined with the experimental results of the encoding performance,the optimal segmentation is determined for the test sequences selected in this thesis.Experimental results have demonstrated that our proposed projection format can achieve an decrease of BD-rate in E2E-SPSNR-NN up to 18.54% and by 8.02% on average for Y,up to 13.08% and by 3.07% on average for U,up to 13.28% and by 4.15%.It can be seen from the experimental results that proposed algorithm has a significant improvement in encoding performance compared with that of ERP format. |
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