Vertex position coding in mesh compression
In a method, a plurality of candidate predictions of a current vertex is determined. The current vertex is included in a plurality of vertices of a mesh. The plurality of candidate predictions is determined based on a plurality of triangles in the mesh. Each of the plurality of predictions corresponds to a respective candidate prediction. A prediction of the current vertex is determined from the plurality of candidate predictions. The prediction is identified by a prediction index that is predetermined based on a number of the plurality of candidate predictions of the current vertex being equal to or larger than a threshold value. Prediction information of the current vertex is encoded based on the determined prediction. The prediction information includes the prediction index identifying the prediction of the current vertex.
1. A method of mesh processing performed in a video encoder, the method comprising:
determining a plurality of candidate predictions of a current vertex, the current vertex being included in a plurality of vertices of a mesh, the plurality of candidate predictions being determined based on a plurality of triangles in the mesh, each of the plurality of triangles corresponding to a respective candidate prediction;
determining a prediction of the current vertex based on the plurality of candidate predictions, the prediction being identified by a prediction index that is predetermined based on a number of the plurality of candidate predictions of the current vertex being equal to or larger than a threshold value; and
encoding prediction information of the current vertex based on the determined prediction, the prediction information including the prediction index identifying the prediction of the current vertex, wherein:
the prediction index is encoded as a first prediction index when the number of the plurality of candidate predictions of the current vertex is equal to the threshold value, the first prediction index indicating the prediction of the current vertex is associated with a first one of a plurality of candidate predictors in a prediction list, and
the prediction index is encoded as a second prediction index when the number of the plurality of candidate predictions of the current vertex is larger than the threshold value, the second prediction index indicating the prediction of the current vertex is associated with a second one of the plurality of candidate predictors in the prediction list.
2. The method of claim 1 , wherein the threshold value is equal to or larger than 2 and equal to or smaller than 5.
3. The method of claim 1 , wherein the determining the plurality of candidate predictions of the current vertex further comprises:
determining a first triangle of the plurality of triangles for the current vertex, the first triangle sharing an edge with a second triangle of the plurality of triangles, the current vertex being included in the second triangle and opposite to the shared edge; and
determining a first candidate prediction of the plurality of candidate predictions based on the determined first triangle via a parallelogram prediction in which the first candidate prediction and the first triangle form a first parallelogram.
4. The method of claim 3 , wherein the determining the plurality of candidate predictions of the current vertex further comprises:
determining an average prediction of the plurality of candidate predictions.
5. The method of claim 4 , wherein the determining the prediction of the current vertex further comprises:
determining the prediction list for the current vertex, the prediction list including the average prediction and the plurality of candidate predictions subsequent to the average prediction in the prediction list, an order of the plurality of candidate predictions in the prediction list being based on an order of the plurality of triangles in the mesh, and each of the plurality of candidate predictors in the prediction list being associated with a respective prediction index.
6. The method of claim 5 , wherein the plurality of triangles is ordered based on an Edgebreaker algorithm in which the plurality of triangles is labelled in a spiraling triangle-spanning-tree order.
7. The method of claim 1 , wherein:
the prediction index is encoded as a third prediction index when the number of the plurality of candidate predictions of the current vertex is equal to or larger than the threshold value, the third prediction index indicating that the prediction of the current vertex is associated with a third one of the plurality of candidate predictors in the prediction list.
8. The method of claim 5 , wherein the determining the prediction of the current vertex further comprises:
determining a prediction difference between each of the plurality of candidate predictors in the prediction list and the current vertex; and
determining the prediction from the plurality of candidate predictors in the prediction list that corresponds to a minimum prediction difference of the prediction differences.
9. The method of claim 5 , wherein the determining the prediction of the current vertex further comprises:
determining the prediction in a subset of the plurality of candidate predictors of the prediction list that has a minimum prediction difference.
10. The method of claim 5 , wherein the determining the respective prediction index further comprises:
determining the respective prediction index for each of the plurality of candidate predictors in the prediction list based on one of a fixed length coding, a variable length coding, and a differential coding.
11. The method of claim 1 , wherein:
the prediction information of the current vertex includes residual information indicating a difference between the current vertex and the determined prediction, and
the method further comprising:
encoding the residual information.
12. A method of mesh processing performed in a video decoder, the method comprising:
receiving a bitstream including coded information of a mesh including a plurality of vertices, the coded information including a prediction index that identifies a prediction of a current vertex;
determining a plurality of candidate predictions of the current vertex of the mesh, the plurality of candidate predictions being determined based on a plurality of triangles in the mesh, each of the plurality of triangles corresponding to a respective candidate prediction;
determining the prediction of the current vertex from a plurality of candidate predictors in a prediction list that is associated with the plurality of candidate predictions, the prediction being identified by the prediction index that is predetermined based on a number of the plurality of candidate predictions of the current vertex being equal to or larger than a threshold value; and
reconstructing the current vertex based on the determined prediction, wherein:
when the number of the plurality of candidate predictions of the current vertex is equal to the threshold value, the prediction index is a first prediction index and the prediction of the current vertex is determined with a first one of the plurality of candidate predictors in the prediction list according to the first prediction index, and
when the number of the plurality of candidate predictions of the current vertex is larger than the threshold value, the prediction index is a second prediction index and the prediction of the current vertex is determined with a second one of the plurality of candidate predictors in the prediction list according to the second prediction index.
13. The method of claim 12 , wherein the threshold value is equal to or larger than 2 and equal to or smaller than 5.
14. The method of claim 12 , wherein the determining the plurality of candidate predictions of the current vertex further comprises:
determining a first triangle of the plurality of triangles for the current vertex, the first triangle sharing an edge with a second triangle of the plurality of triangles, the current vertex being included in the second triangle and opposite to the shared edge; and
determining a first candidate prediction of the plurality of candidate predictions based on the determined first triangle via a parallelogram prediction in which the first candidate prediction and the first triangle form a first parallelogram.
15. The method of claim 14 , wherein the determining the plurality of candidate predictions of the current vertex further comprises:
determining an average prediction of the plurality of candidate predictions.
16. The method of claim 15 , wherein the determining the prediction of the current vertex further comprises:
determining the prediction list for the current vertex, the prediction list including the average prediction and the plurality of candidate predictions subsequent to the average prediction in the prediction list, an order of the plurality of candidate predictions in the prediction list being based on an order of the plurality of triangles in the mesh, and each of the plurality of candidate predictors in the prediction list being associated with a respective prediction index.
17. The method of claim 16 , wherein the plurality of triangles is ordered based on an Edgebreaker algorithm in which the plurality of triangles is labelled in a spiraling triangle-spanning-tree order.
18. The method of claim 12 , wherein:
when the number of the plurality of candidate predictions of the current vertex is equal to or larger than the threshold value, the prediction index is a third prediction index and the prediction of the current vertex is determined with a third one of the plurality of candidate predictors in the prediction list according to the third prediction index.
19. The method of claim 16 , wherein the determining the prediction of the current vertex further comprises:
determining a prediction difference between each of the plurality of candidate predictors in the prediction list and the current vertex; and
determining the prediction from the plurality of candidate predictors in the prediction list that corresponds to a minimum prediction difference of the prediction differences.
20. A method of processing mesh data, the method comprising:
processing a bitstream of the mesh data according to a format rule, wherein:
the bitstream includes coded information of a mesh with a plurality of vertices, the coded information including a prediction index that identifies a prediction of a current vertex of the mesh; and
the format rule specifies that:
a plurality of candidate predictions is determined for the current vertex of the mesh, the plurality of candidate predictions being determined based on a plurality of triangles in the mesh, each of the plurality of triangles corresponding to a respective candidate prediction;
the prediction of the current vertex is determined from a plurality of candidate predictors in a prediction list that is associated with the plurality of candidate predictions, the prediction being identified by the prediction index that is predetermined based on a number of the plurality of candidate predictions of the current vertex being equal to or larger than a threshold value; and
the current vertex is processed based on the determined prediction, wherein:
when the number of the plurality of candidate predictions of the current vertex is equal to the threshold value, the prediction index is a first prediction index and the prediction of the current vertex is determined with a first one of the plurality of candidate predictors in the prediction list according to the first prediction index, and
when the number of the plurality of candidate predictions of the current vertex is larger than the threshold value, the prediction index is a second prediction index and the prediction of the current vertex is determined with a second one of the plurality of candidate predictors in the prediction list according to the second prediction index.