Adaptive perturbed cube map projection

1. A method for processing video data, comprising:

obtaining a video bitstream including a plurality of video frames of a spherical representation of 360-degree video data, a video frame of the plurality of video frames including a plurality of planar surfaces of a geometry, wherein each planar surface of the plurality of planar surfaces includes a plurality of pixels;

determining three-dimensional coordinates of a target point of the spherical representation;

determining a planar surface of the geometry to which the target point is to be mapped, the planar surface being determined based on the three-dimensional coordinates of the target point;

extracting an adaptation parameter from the video bitstream, wherein the video bitstream includes an indication of the adaptation parameter in a header associated with a tile or a slice of the video frame or a parameter set associated with the video frame or with the plurality of video frames;

determining two-dimensional coordinates of a mapping location on the planar surface to which the target point is to be mapped based on the three-dimensional coordinates of the target point and the adaptation parameter;

generating a pixel value based on one or more pixels of the plurality of pixels associated with the mapping location on the planar surface; and

assigning the pixel value to the target point of the spherical representation.

2. The method of claim 1 , wherein determining the two-dimensional coordinates of the mapping location on the planar surface includes:

determining initial two-dimensional coordinates of the mapping location based on the three-dimensional coordinates of the target point; and

determining the two-dimensional coordinates of the mapping location by modifying the initial two-dimensional coordinates using the adaptation parameter.

3. The method of claim 2 , wherein determining the initial two-dimensional coordinates based on the three-dimensional coordinates of the target point includes:

determining a first initial two-dimensional coordinate of the initial two-dimensional coordinates based on a first ratio between a first three-dimensional coordinate of the three-dimensional coordinates and a second three-dimensional coordinate of the three-dimensional coordinates; and

determining a second initial two-dimensional coordinate of the initial two-dimensional coordinates based on a second ratio between a third three-dimensional coordinate of the three-dimensional coordinates and the second three-dimensional coordinate of the three-dimensional coordinates.

4. The method of claim 2 , wherein determining the two-dimensional coordinates of the mapping location by modifying the initial two-dimensional coordinates using the adaptation parameter includes:

determining a first two-dimensional coordinate of the two-dimensional coordinates of the mapping location by modifying the first initial two-dimensional coordinate using a function, wherein the first initial two-dimensional coordinate is modified by implementing the function as a function of the adaptation parameter and the first initial two-dimensional coordinate; and

determining a second two-dimensional coordinate of the two-dimensional coordinates of the mapping location by modifying the second initial two-dimensional coordinate using the function, wherein the second initial two-dimensional coordinate is modified by implementing the function as a function of the adaptation parameter and the second initial two-dimensional coordinate.

5. The method of claim 4 , wherein the function includes a signum (sgn) function and a quadratic function, and wherein the adaptation parameter is set to a first value based on the quadratic function.

6. The method of claim 4 , wherein the function includes an arctangent (a tan) function, and wherein the adaptation parameter is set to a second value based on the arctangent function.

7. The method of claim 4 , wherein the function includes a piecewise linear model including multiple pivot points, and wherein at least one of the multiple pivot points is defined by the adaptation parameter.

8. The method of claim 1 , further comprising:

receiving a supplemental enhancement information message, the supplemental enhancement information message including an indication of the adaptation parameter; and

extracting the adaptation parameter from the supplemental enhancement information message.

9. The method of claim 1 , wherein the geometry includes a cube, wherein the plurality of planar surfaces correspond to six surfaces of the cube, and wherein each surface of the six surfaces is tangential to a sphere of the spherical representation.

10. An apparatus for processing video data, comprising:

memory to store 360-degree video data; and

a processor configured to:

obtain a video bitstream including a plurality of video frames of a spherical representation of the 360-degree video data, a video frame of the plurality of video frames including a plurality of planar surfaces of a geometry, wherein each planar surface of the plurality of planar surfaces includes a plurality of pixels;

determine three-dimensional coordinates of a target point of the spherical representation;

determine a planar surface of the geometry to which the target point is to be mapped, the planar surface being determined based on the three-dimensional coordinates of the target point;

extract an adaptation parameter from the video bitstream, wherein the video bitstream includes an indication of the adaptation parameter in a header associated with a tile or a slice of the video frame or a parameter set associated with the video frame or with the plurality of video frames;

determine two-dimensional coordinates of a mapping location on the planar surface to which the target point is to be mapped based on the three-dimensional coordinates of the target point and the adaptation parameter;

generate a pixel value based on one or more pixels of the plurality of pixels associated with the mapping location on the planar surface; and

assign the pixel value to the target point of the spherical representation.

11. The apparatus of claim 10 , wherein the processor is further configured to:

determine initial two-dimensional coordinates of the mapping location based on the three-dimensional coordinates of the target point; and

determine the two-dimensional coordinates of the mapping location by modifying the initial two-dimensional coordinates using the adaptation parameter.

12. The apparatus of claim 11 , wherein the processor is further configured to:

determine a first initial two-dimensional coordinate of the initial two-dimensional coordinates based on a first ratio between a first three-dimensional coordinate of the three-dimensional coordinates and a second three-dimensional coordinate of the three-dimensional coordinates; and

determine a second initial two-dimensional coordinate of the initial two-dimensional coordinates based on a second ratio between a third three-dimensional coordinate of the three-dimensional coordinates and the second three-dimensional coordinate of the three-dimensional coordinates.

13. The apparatus of claim 11 , wherein the processor is further configured to:

determine a first two-dimensional coordinate of the two-dimensional coordinates of the mapping location by modifying the first initial two-dimensional coordinate using a function, wherein the first initial two-dimensional coordinate is modified by implementing the function as a function of the adaptation parameter and the first initial two-dimensional coordinate; and

determine a second two-dimensional coordinate of the two-dimensional coordinates of the mapping location by modifying the second initial two-dimensional coordinate using the function, wherein the second initial two-dimensional coordinate is modified by implementing the function as a function of the adaptation parameter and the second initial two-dimensional coordinate.

14. The apparatus of claim 13 , wherein the function includes a signum (sgn) function and a quadratic function, and wherein the adaptation parameter is set to a first value based on the quadratic function.

15. The apparatus of claim 13 , wherein the function includes an arctangent (a tan) function, and wherein the adaptation parameter is set to a second value based on the arctangent function.

16. The apparatus of claim 13 , wherein the function includes a piecewise linear model including multiple pivot points, and wherein at least one of the multiple pivot points is defined by the adaptation parameter.

17. The apparatus of claim 10 , wherein the processor is further configured to:

receive a supplemental enhancement information message, the supplemental enhancement information message including an indication of the adaptation parameter; and

extract the adaptation parameter from the supplemental enhancement information message.

18. The apparatus of claim 10 , wherein the geometry includes a cube, wherein the plurality of planar surfaces correspond to six surfaces of the cube, and wherein each surface of the six surfaces is tangential to a sphere of the spherical representation.

19. The apparatus of claim 10 , wherein the apparatus comprises a mobile device with one or more cameras to capture the 360-degree video data.

20. The apparatus of claim 10 , wherein the apparatus comprises a mobile device with a display device to output the pixel value at the target point of the spherical representation.

21. A non-transitory computer-readable medium having stored thereon instructions that, when executed by one or more processors, cause the one or more processor to:

obtain a video bitstream including a plurality of video frames of a spherical representation of the 360-degree video data, a video frame of the plurality of video frames including a plurality of planar surfaces of a geometry, wherein each planar surface of the plurality of planar surfaces includes a plurality of pixels;

determine three-dimensional coordinates of a target point of the spherical representation;

determine a planar surface of the geometry to which the target point is to be mapped, the planar surface being determined based on the three-dimensional coordinates of the target point;

extract an adaptation parameter from the video bitstream, wherein the video bitstream includes an indication of the adaptation parameter in a header associated with a tile or a slice of the video frame or a parameter set associated with the video frame or with the plurality of video frames;

determine two-dimensional coordinates of a mapping location on the planar surface to which the target point is to be mapped based on the three-dimensional coordinates of the target point and the adaptation parameter;

generate a pixel value based on one or more pixels of the plurality of pixels associated with the mapping location on the planar surface; and

assign the pixel value to the target point of the spherical representation.

22. An apparatus comprising:

means for obtaining a video bitstream including a plurality of video frames of a spherical representation of 360-degree video data, a video frame of the plurality of video frames including a plurality of planar surfaces of a geometry, wherein each planar surface of the plurality of planar surfaces includes a plurality of pixels;

means for determining three-dimensional coordinates of a target point of the spherical representation;

means for determining a planar surface of the geometry to which the target point is to be mapped, the planar surface being determined based on the three-dimensional coordinates of the target point;

means for extracting an adaptation parameter from the video bitstream, wherein the video bitstream includes an indication of the adaptation parameter in a header associated with a tile or a slice of the video frame or a parameter set associated with the video frame or with the plurality of video frames;

means for determining two-dimensional coordinates of a mapping location on the planar surface to which the target point is to be mapped based on the three-dimensional coordinates of the target point and an adaptation parameter;

means for generating a pixel value based on one or more pixels of the plurality of pixels associated with the mapping location on the planar surface; and

means for assigning the pixel value to the target point of the spherical representation.