BACKGROUND

The present invention relates to video processing, and more particularly, to a video processing method for processing a projection-based frame having projection faces packed in a hemisphere cubemap projection layout with face packing constraints (e.g., constraints on face index and/or face rotation) and an associated video processing apparatus.

Virtual reality (VR) with head-mounted displays (HMDs) is associated with a variety of applications. The ability to show wide field of view content to a user can be used to provide immersive visual experiences. A real-world environment has to be captured in all directions, resulting in an omnidirectional video corresponding to a viewing sphere. With advances in camera rigs and HMDs, the delivery of VR content may soon become the bottleneck due to the high bitrate required for representing such a 360-degree content. When the resolution of the omnidirectional video is 4K or higher, data compression/encoding is critical to bitrate reduction.

In general, the omnidirectional video corresponding to a sphere is transformed into a frame with a 360-degree image content represented by one or more projection faces arranged in a 360-degree Virtual Reality (360 VR) projection layout, and then the resulting frame is encoded into a bitstream for transmission. The bitstream generated from an encoder side is received and decoded by a decoder side. In addition, a configuration of the employed 360 VR projection layout may also be signaled from the encoder side to the decoder side. When the employed 360 VR projection layout is a hemisphere cubemap projection layout, projection faces packed in a projection-based frame includes one full face and four half faces, where a shape of the full face is a square, and a shape of each half face is not a square. To ensure image quality of the projection-based frame that employs the hemisphere cubemap projection layout, there is a need for an innovative design for applying face packing constrains to the hemisphere cubemap projection layout.

SUMMARY

One of the objectives of the claimed invention is to provide a video processing method for processing a projection-based frame having projection faces packed in a hemisphere cubemap projection layout with face packing constraints (e.g., constraints on face index and/or face rotation) and an associated video processing apparatus.

According to a first aspect of the present invention, an exemplary video processing method is disclosed. The exemplary video processing method includes a step of receiving a bitstream, and a step of decoding, by a decoding circuit, a part of the bitstream to generate a decoded frame, including parsing a plurality of syntax elements from the bitstream. The decoded frame is a projection-based frame that comprises a plurality of projection faces packed at a plurality of face positions with different position indexes in a hemisphere cubemap projection layout. A portion of a 360-degree content of a sphere is mapped to the plurality of projection faces via hemisphere cubemap projection. Values of the plurality of syntax elements are indicative of face indexes of the plurality of projection faces packed at the plurality of face positions, respectively, and are constrained to meet a requirement of bitstream conformance.

According to a second aspect of the present invention, an exemplary video processing method is disclosed. The exemplary video processing method includes a step of receiving a bitstream, and a step of decoding, by a decoding circuit, a part of the bitstream to generate a decoded frame, including parsing a plurality of first syntax elements from the bitstream. The decoded frame is a projection-based frame that comprises a plurality of projection faces packed at a plurality of face positions with different position indexes in a hemisphere cubemap projection layout. A portion of a 360-degree content of a sphere is mapped to the plurality of projection faces via hemisphere cubemap projection. Values of the plurality of first syntax elements are indicative of rotation angles of the plurality of projection faces packed at the plurality of face positions, respectively. A portion of the values of the plurality of first syntax elements are constrained to meet a requirement of bitstream conformance.

According to a third aspect of the present invention, an exemplary video processing apparatus is disclosed. The exemplary video processing apparatus includes a decoding circuit arranged to receive a bitstream and decode a part of the bitstream to generate a decoded frame. The decoding circuit parses a plurality of first syntax elements and a plurality of second syntax elements from the bitstream, wherein the decoded frame is a projection-based frame that comprises a plurality of projection faces packed at a plurality of face positions with different position indexes in a hemisphere cubemap projection layout; a portion of a 360-degree content of a sphere is mapped to the plurality of projection faces via hemisphere cubemap projection; values of the plurality of second syntax elements are indicative of face indexes of the plurality of projection faces packed at the plurality of face positions, respectively, and are constrained to meet a requirement of bitstream conformance; values of the plurality of first syntax elements are indicative of rotation angles of the plurality of projection faces packed at the plurality of face positions, respectively; and a portion of the values of the plurality of first syntax elements are constrained to meet the requirement of bitstream conformance.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

