Abstract
Currently available 360° cameras normally capture several images covering a scene in all directions around a shooting point. The captured images are spherical in nature and are mapped to a two-dimensional plane using various projection methods. Many projection formats have been proposed for 360° videos. However, standards for a quality assessment of 360° images are limited. In this paper, various projection formats are compared to explore the problem of distortion caused by a mapping operation, which has been a considerable challenge in recent approaches. The performances of various projection formats, including equi-rectangular, equal-area, cylindrical, cube-map, and their modified versions, are evaluated based on the conversion causing the least amount of distortion when the format is changed. The evaluation is conducted using sample images selected based on several attributes that determine the perceptual image quality. The evaluation results based on the objective quality metrics have proved that the hybrid equi-angular cube-map format is the most appropriate solution as a common format in 360° image services for where format conversions are frequently demanded. This study presents findings ranking these formats that are useful for identifying the best image format for a future standard.
Highlights
In various applications, including social networking services, teleconferencing, broadcasting, map services, education, professional training, and online games, 360◦ immersive content has recently become popular
When adjusted cube-map projection (ACP), cube-map projection (CMP), equi-angular cube-map projection (EAC), or equatorial cylindrical projection (ECP) are used for Projection–X, the results of the hybrid equi-angular cube map projection (HEC) are the highest for the PSNR, structural similarity index metric (SSIM), and visual information fidelity (VIF) metrics
In the case of the weighted-to-spherical PSNR (WS-PSNR) shown in Table 4, the individual ranking is different from the other three metrics, except for the equi-rectangular projection (ERP) and ECP formats
Summary
In various applications, including social networking services, teleconferencing, broadcasting, map services, education, professional training, and online games, 360◦ immersive content has recently become popular. 360◦ content, that is, a bounding sphere containing the entire scene with 360◦ horizontal and 180◦ vertical directions to provide a rich user experience. VR applications pursuing real-life simulations on advanced digital devices have been an increasingly intriguing topic [1,2,3,4,5,6,7,8,9]. VR services are rapidly growing in number, providing high-quality. The demand for 360◦ content has proliferated with increased attention; it should be noted that there are still numerous impediments for 360◦. Head-mounted devices such as HTC Vive, Samsung Gear
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