Apparatus, a method and a computer program for volumetric video

1. A method comprising:

providing a three-dimensional representation of at least one object as an input for an encoder;

projecting the three-dimensional representation onto at least one two-dimensional patch;

generating at least a geometry image and a texture image from the at least one two-dimensional patch;

generating, based on the geometry image, a mesh comprising a number of vertices;

compressing the mesh comprising the number of vertices;

mapping the compressed number of vertices to two-dimensional coordinates of the texture image, wherein the texture image comprises a different level of compression than the mesh comprising the number of vertices, wherein a resolution of the texture image is different from the compressed number of vertices of the mesh; and

signaling said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh in or along a bitstream.

2. The method according to claim 1 , further comprising:

determining the resolution of the texture image; and

determining the number of vertices of the mesh, wherein the ratio between the resolution of the texture image and the number of vertices of the mesh is adjustable with the compressing of the mesh, wherein the resolution of the texture image is higher than a resolution of the compressed mesh.

3. The method according to claim 1 , wherein said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh are configured to be signaled in metadata structures.

4. The method according to claim 3 , wherein said two-dimensional coordinates of the texture image are configured to be signaled as video-based point cloud coding metadata structures comprising definitions for calculating two-dimensional texture coordinates from vertex coordinates of the compressed geometry image.

5. The method according to claim 3 , wherein the signalling of said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh is configured to be carried out with at least two syntax elements, a first syntax element defining whether said mapping is used and a second syntax element defining a type of the mapping.

6. The method according to claim 5 , wherein the signalling of said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh is configured to be included in an atlas sequence parameter set syntax structure.

7. An apparatus comprising

at least one processor and

at least one memory,

said at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:

provide a three-dimensional representation of at least one object as an input for an encoder;

project the three-dimensional representation onto at least one two-dimensional patch;

generate at least a geometry image and a texture image from the at least one two-dimensional patch;

generate, based on the geometry image, a mesh comprising a number of vertices;

compress the mesh comprising the number of vertices;

map the compressed number of vertices to two-dimensional coordinates of the texture image, wherein the texture image comprises a different level of compression than the mesh comprising the number of vertices, wherein a resolution of the texture image is different from the compressed number of vertices of the mesh; and

signal said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh in or along a bitstream.

8. The apparatus according to claim 7 , wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to:

determine the resolution of the texture image; and

determine the number of vertices of the mesh, wherein the ratio between the resolution of the texture image and the number of vertices of the mesh is adjustable with the compressing of the mesh.

9. The apparatus according to claim 7 , wherein said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh are configured to be signaled in metadata structures.

10. The apparatus according to claim 9 , wherein said two-dimensional coordinates of the texture image are configured to be signaled as video-based point cloud coding metadata structures comprising definitions for calculating two-dimensional texture coordinates from vertex coordinates of the compressed geometry image.

11. The apparatus according to claim 9 , wherein signaling said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh comprises the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to:

use at least two syntax elements, a first syntax element defining whether said mapping is used and a second syntax element defining a type of the mapping.

12. The apparatus according to claim 11 , wherein signaling said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh comprises the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to:

include said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh in an atlas sequence parameter set syntax structure.

13. The apparatus according to claim 9 , wherein signaling said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh comprises the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to:

use at least a first syntax element defining whether said mapping is used and a syntax structure defining a list of mapping types.

14. The apparatus according to claim 13 , wherein signaling said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh comprises the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to:

use a patch metadata or a tile group metadata.

15. The apparatus according to claim 7 , wherein said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh are configured to be signaled as an additional attribute for encoded volumetric data bitstream.

16. The apparatus according to claim 15 , wherein a UV attribute map comprising per pixel two-dimensional coordinates of the texture image are configured to be stored on at least two channels of an encoded video bitstream.

17. The apparatus according to claim 15 , wherein a map comprising said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh are encodable with a plurality of values, wherein said values represent at least one per-pixel property.

18. The apparatus according to claim 17 , wherein said map is configured to be embedded in an occupancy map.

19. The apparatus according to claim 7 , wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to:

provide a signal to control a decoder not to scale up one or more of encoded video component streams.

20. The apparatus according to claim 19 , wherein signaling said two-dimensional coordinates of the texture image to be applied to the compressed number of vertices of the mesh comprises the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to:

use a flag in one or more of the following:

occupancy information;

geometry information; or

attribute information.