A 360 video projection is any of many ways to map a spherical field of view to a flat image. It is used to encode and deliver the effect of a spherical, 360-degree image to viewers such as needed for

360-degree video 360-degree videos, also known as surround video, or immersive videos or spherical videos, are video recordings where a view in every direction is recorded at the same time, shot using an omnidirectional camera or a collection of cameras. During pl ...

s and for

virtual reality Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), educ ...

. A 360 video projection is a specialized form of a

map projection In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longitud ...

, with characteristics tuned for the efficient representation, transmission, and display of 360° fields of view.

Different projections

Equirectangular

An equirectangular projection simply maps the yaw and pitch (longitude and latitiude) of a sphere linearly to a rectangular image. It produces a signature curved look. In addition, the distribution of pixel density (which can be visualized with

Tissot's indicatrix In cartography, a Tissot's indicatrix (Tissot indicatrix, Tissot's ellipse, Tissot ellipse, ellipse of distortion) (plural: "Tissot's indicatrices") is a mathematical contrivance presented by French mathematician Nicolas Auguste Tissot in 1859 a ...

) is suboptimal, with the usually more important "equator" getting the lowest density.

Cube Map

Cube mapping records the environment as the six faces of a cube. The image distortion is markedly reduced, especially when looking at the faces head-on. Still, the edges and corners of faces receive more pixels than the center.

Equi-Angular Cubemap (EAC)

The Equi-Angular Cubemap (EAC) projection is a variant of the cubemap that distributes the pixels evenly by angle. This keeps the density of information consistent, regardless of which direction the viewer is looking. It was detailed by

Google Google LLC () is an American multinational technology company focusing on search engine technology, online advertising, cloud computing, computer software, quantum computing, e-commerce, artificial intelligence, and consumer electronics. ...

on March 14, 2017. In January 2018 the company started using the spherical projection to stream 360 degree videos on

YouTube YouTube is a global online video platform, online video sharing and social media, social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by ...

. GoPro adopted the EAC format in 2019 when they released the GoPro MAX. They noted that EAC enabled then in using 25% less pixels by packing the equivalent of 5376x2688 pixels into an EAC projection of 4032x2688 pixels. This projection was then split horizontally in two streams of 4032x1344 and encoded, which could be decoded by regular UHD decoders. Mainstream video tools have not yet added support for EAC formats, such as GoPro's .360. A custom fork of FFmpeg and a tool called max2sphere however do enable .360 processing.

Pyramid format

The Pyramid projection is a variation of the cubemap using a

pyramid A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilat ...

geometry. The video is rendered in multiple viewports (in Facebook's case 30) where the base of the

contains the full resolution and is right in front of the viewer, while the sides are rendered with a gradually decreasing resolution. It was detailed by Facebook on January 21, 2016, mainly aimed at VR video.{{Cite web, url=https://code.facebook.com/posts/1126354007399553/next-generation-video-encoding-techniques-for-360-video-and-vr/, title=Next-generation video encoding techniques for 360 video and VR, website=Facebook Code, language=en, access-date=2018-04-02 The company claims an 80% reduction in bandwidth with this projection, with the disadvantage that many more viewports need to be rendered and stored.

References