Abstract
Panoramic videos provide users with an amazing experience with immersive and interactive viewing, and are now gaining global popularity. Since panoramic videos are spherical in nature while effectively processed in planar projection formats in applications, it is crucial to implement sphere-to-plane projection, where a good interpolation algorithm is of great importance regarding generating high quality planar perspective videos. Moreover, different planar projection formats adapt to different applications according to their own characteristics. It is common to convert one projection format to another, where interpolation algorithms also make a difference on performance. In this paper, an interpolation algorithm named spherical Lanczos (SLAN) is proposed to achieve advanced performance in sphere-to-plane projection or planar projection format conversions of panoramic videos. In SLAN, we fully consider panoramic videos are naturally spherical. Reference pixels are selected carefully, and the weights are calculated correctly. Experimental results demonstrate that the SLAN interpolation algorithm is beneficial for the whole processing chain of panoramic videos both with lossless compression coding and with loss compression coding in terms of the increase in various end-to-end PSNR and the decrease in BD_rate. The cubic projection (CBP) and adjusted cubemap projection (ACP) are also evaluated to illustrate that the proposed algorithm is applicable for all kinds of planar projection format due to their inevitable deformation.
Highlights
The recent years have witnessed an explosion of various video services, especially for immersive panoramic videos
Many sphere-to-plane projection formats have been proposed in recent years, such as the equirectangular projection (ERP) format [12], cubic projection (CBP) format [13], adjusted cubemap projection (ACP) format [14], Craster parabolic projection (CPP) format [15], octahedron projection (OHP) format [16], icosahedral projection (ISP) format [17], segmented sphere projection (SSP) format [18], rotated sphere projection (RSP) format [19], equi-angular cubemap (EAC) format [20] and octagonal projection format (OGP) [21]
EXPERIMENTAL RESULTS In order to evaluate the performance of the proposed spherical Lanczos (SLAN) interpolation algorithm, we compared with Lanczos interpolation algorithm which is generally adopted in 360Lib-4.0 software
Summary
The recent years have witnessed an explosion of various video services, especially for immersive panoramic videos. Lanczos interpolation algorithm [24], as a popular interpolation algorithm, has been considered as a good compromise between the computational complexity and performance among several available interpolation algorithms [25] It is generally adopted by the JVET to achieve sphere-to-plane projection or format conversions in 360Lib-4.0 software [26]. Considering that panoramic videos are spherical, though effectively processed in the planar projection format, the pixels are related on the sphere originally. A spherical Lanczos (SLAN) interpolation algorithm is proposed achieving advanced performance in sphere-to-plane projection or planar projection format conversions of panoramic videos. It is noted that the proposed SLAN interpolation algorithm is detailed in the format conversion from CPP to ERP for example in this paper, and it is applicable for all kinds of planar projection format conversions of panoramic videos.
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