Research On Projection And Coding Of Panoramic Video

As a new multimedia technology,panoramic videos have brought people a completely new immersive experience.However,modern video coding standards which are designed for the planar videos cannot be applied to the panoramic videos directly because they are spherical in nature.For being encoded with these modern video coding standards,panoramic videos are generally projected into a rectangular plane,resulting in the planar perspective videos.However,there is always deformation or distortion in the planar perspective videos after sphere-to-plane projection which further results in a penalized encoding performance of panoramic videos.Therefore,it is of great significance to select the appropriate planar projection format and optimize the encoding performance of panoramic vides.As an equalarea projection,Craster's Parabolic Projection(CPP)achieves approximately uniform spherical sampling without wasted pixels.However,the planar perspective frame in CPP format is not in a rectangle,so that it cannot be encoded directly using off-the-shelf encoders.For solving this problem,an encoding optimization scheme of CPP format is proposed in this thesis.In order to realize the rectangularization of frames in CPP format,schemes based on padding and stretching are proposed in this thesis.Firstly,the frame in CPP format is divided into equally spaced strips along the parallels.Then two padding schemes are proposed for each strip,one exploiting adjacent pixels on the sphere and the other exploiting neighboring pixels in the frame in CPP format.After padded,strips are in rectangles.Experimental results have demonstrated that both of two padding schemes can achieve better encoding performance which is penalized due to the strong edges in frames in CPP format.Further compared with the strips at the same latitudes in the frame in ERP format,proposed two padding schemes can achieve BD-rate reductions by 2.01% and 3.51% on average for Y respectively,5.00% and 6.10% for U respectively,5.21% and 6.09% for V respectively.The performance of interpolation algorithms which are utilized for rectangularization has a great influence on the quality of stretched frames.In this thesis,two stretching schemes based on onedimensional(1-D)nearest-neighbor interpolation algorithm and Lanczos interpolation algorithm are proposed respectively.Experimental results have demonstrated that compared with the original CPP strips,proposed two stretching schemes can achieve BD-rate reductions by 6.61% and 29.7% on average for Y,respectively.Further compared with ERP strips at the same latitudes,proposed stretching scheme utilizing Lanczos interpolation algorithm can achieve a BD-rate reduction by 8.91% on average for Y,9.52% for U and 11.06% for V.In order to further improve the encoding performance of frames in CPP format,the influence of different stripe partitioning methods on the encoding performance of frames in CPP is detailed.Based on the rectangularized stripes,the optimal coding schemes based on the single partitioning and the fixed interval partitioning are proposed.Experiments results have demonstrated that compared with the whole undivided frames in CPP format,proposed two optimal coding schemes can achieve BD-rate reductions by 7.63% and 7.88% on average for Y,respectively.Further compared with the whole frames in ERP format,proposed two optimal coding schemes can achieve BD-rate reductions of 3.59% and 3.74% on average for Y respectively,3.90% and 4.53% for U respectively,3.46% and 2.25% for V respectively.