Research On Coding-Oriented Uniform Sampling Projection Method For Omnidirectional Video

In recent years,as a medium that can show a 360-degree angle of view,omnidirectional video has shown its unique charm in the fields of surveillance,scene display,and live events,having gradually stepped into the public view.Omnidirectional video has the characteristic of wide view,high resolution,high frame rate,and large amount of data,which brings difficulties to storage and transmission.Therefore,an effective omnidirectional video coding scheme is urgently needed.In the omnidirectional video coding process,the projection method and the coding algorithm are the two most critical elements.Focusing on the characteristics of omnidirectional video,this paper proposes the following projection methods to adapt to the subsequent omnidirectional video coding:(1)A dually octagonal projection with less distortion and approximately uniform sampling is proposed.The craster parabolic projection achieves uniform sampling on the sphere,but the content on the two sides of the plane is severely distorted.In terms of this issue,this thesis proposes to project the omnidirectional video onto two octagons,achieving a balance between distortion and uniform sampling,so that the coding performance is improved.In order to eliminate the oblique boundary of the dually octagonal projection,a compact projection is proposed to further save the bitrate.The experimental results show that,compared with the equirectangular projection,the dually octagonal projection can save 24.70% of the bitrate,while the compact dually octagonal projection can save 24.95% of the bitrate.(2)An equal-area uniform cubemap projection is proposed,which leverages the proposed spherical pixel modeling method and the principle of equal-area ratio to solve the problem of non-uniform sampling in the cubemap projection.The proposed cubemap achieves uniform sampling by directly sampling on the sphere and allocating the equal spherical area to each pixel.Due to the directivity of the proposed projection method,it has two sampling modes,the horizontal mode and the vertical mode.The comparative experimental results show that in high-resolution omnidirectional video coding,the proposed projection can obtain the best coding performance.Compared with the equiangular cubemap projection,the two modes can save an average bitrate of0.5509% and 0.6681%,respectively.In addition,according to the characteristics of the proposed projection,adaptive alteration to the spherical Lanczos interpolation algorithm are made,which can provide about 0.1d B of quality gain for the reconstructed video.(3)A circular uniform symmetric cubemap projection is proposed.Although the equal-area uniform cubemap projection realizes uniform sampling on the sphere,it has serious directivity and sampling asymmetry.Besides,it is difficult to determine the best sampling mode in advance for a test sequence.For the aforementioned problems,the proposed projection method divides the spherical surface into circles,and then projects the pixels on the planar diagonal onto the diagonal of the spherical surface,so as to achieve symmetric sampling.At the same time,the spherical pixel modeling method and the principle of equal-area ratio are used to determine the position of circular boundaries and the spherical pixels,so that the uniform sampling is ensured.Experimental results show that in high-resolution omnidirectional video coding,the proposed projection can save the bitrate by 0.8277% compared with the equiangular cubemap projection.