Apparatus and method for encoding and decoding a picture using picture boundary handling

1. An apparatus for encoding a picture, configured to

partition the picture into leaf blocks using recursive multi-tree partitioning,

block-based encode the picture into a data stream using the partitioning of the picture into the leaf blocks,

wherein the apparatus is configured to, in partitioning the picture into the leaf blocks,

for a predetermined block that corresponds to a predetermined tree level of the multi-tree partitioning and which extends beyond a boundary of the picture, reduce an available set of split modes for splitting the predetermined block depending on a position at which the boundary of the picture crosses the predetermined block in order to acquire a reduced set of one or more split modes,

wherein, if a cardinality of the reduced set is one, the apparatus is configured to apply the split mode of the reduced set for splitting the predetermined block, and

if a cardinality of the reduced set is greater than one, the apparatus is configured to select one of the split modes of the reduced set and to apply the selected one of the split modes for splitting the predetermined block and to signal the selection in the data stream.

2. The apparatus of claim 1 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes at least one of

a first split mode which does not impose any restriction onto one or more subsequent splits for subsequent tree levels succeeding the predetermined tree level, and

a second split mode that splits the predetermined block into two subblocks along a split line that is parallel to the picture boundary's position in the predetermined block and which split line is at least one of collocated to the boundary of the picture and centered inside the predetermined block.

3. The apparatus of claim 1 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes

one predetermined split mode that splits the predetermined block into two subblocks along a first split line that is parallel to the picture boundary's position in the predetermined block and which split line is at least one of collocated to the boundary of the picture and centered inside the predetermined block.

4. The apparatus of claim 3 ,

wherein the predetermined split mode is either a vertical bi-split or a horizontal bi-split.

5. The apparatus of claim 1 , wherein the apparatus is configured to determine the available set of split modes for the predetermined block

independent from a location of the predetermined block relative to the picture boundary, and/or

dependent on a sequence of split modes of preceding tree levels from which the predetermined block emerges.

6. The apparatus of claim 1 , wherein the apparatus is configured to determine the available set of split modes for the predetermined block

to be equal to a primitive set of split modes comprising a quad split, at least one horizontal bi-split and at least one vertical bi-split, if all split modes of preceding tree levels from which the predetermined block emerges are outside a restrictive set of bi-splits, and

to be equal to the primitive set of split modes less the quad split, if a split mode of a preceding tree level from which the predetermined block emerges is one of the restrictive set of bi-splits.

7. The apparatus of claim 6 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes at least one of

the quad split, and

a bi-split that splits the predetermined block into two subblocks along a split line that is parallel to the picture boundary's position in the predetermined block and which split line is at least one of collocated to the picture boundary and centered inside the predetermined block.

8. The apparatus of claim 7 , wherein, if a bi-split from the reduced set is applied and the number of consecutive bi-splits is restricted to a predetermined maximum number of consecutive bi-splits, the apparatus is configured to not count a consecutive bi-split if said consecutive bi-split is applied over a picture boundary.

9. The apparatus of claim 6 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes the quad split only if the predetermined block extends beyond a corner of the picture 12 .

10. An apparatus for decoding a picture, configured to

partition the picture into leaf blocks using recursive multi-tree partitioning,

block-based decode the picture from a data stream using the partitioning of the picture into leaf blocks,

wherein the apparatus is configured to, in partitioning the picture into the leaf blocks,

for a predetermined block that corresponds to a predetermined tree level of the multi-tree partitioning and which extends beyond a boundary of the picture, reduce an available set of split modes for splitting the predetermined block depending on a position at which the picture boundary crosses the predetermined block to acquire a reduced set of one or more split modes, wherein

if a cardinality of the reduced set is one, the apparatus is configured to apply the split mode of the reduced set for splitting the predetermined block, and

if a cardinality of the reduced set is greater than one, the apparatus is configured to select one of the split modes of the reduced set and to apply the selected one of the split modes for splitting the predetermined block according to a signalization in the data stream.

11. The apparatus of claim 10 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes at least one of

a first split mode which does not impose any restriction onto one or more subsequent splits for subsequent tree levels succeeding the predetermined tree level, and

a second split mode that splits the predetermined block into two subblocks along a split line that is parallel to the picture boundary's position in the predetermined block and which split line is at least one of collocated to the picture boundary and centered inside the predetermined block.

12. The apparatus of claim 10 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes

one predetermined split mode that splits the predetermined block into two subblocks along a first split line that is parallel to the picture boundary's position in the predetermined block and which split line is at least one of collocated to the boundary of the picture and centered inside the predetermined block.

13. The apparatus of claim 12 ,

wherein the predetermined split mode is either a vertical bi-split or a horizontal bi-split.

14. The apparatus of claim 10 , wherein the apparatus is configured to determine the available set of split modes for the predetermined block

independent from a location of the predetermined block relative to the picture boundary, and/or

dependent on a sequence of split modes of preceding tree levels from which the predetermined block emerges.

15. The apparatus of claim 10 , wherein the apparatus is configured to determine the available set of split modes for the predetermined block

to be equal to a primitive set of split modes comprising a quad split, at least one horizontal bi-split and at least one vertical bi-split, if all split modes of preceding tree levels from which the predetermined block emerges are outside a restrictive set of bi-splits, and

to be equal to the primitive set of split modes less the quad split, if a split mode of a preceding tree level from which the predetermined block emerges is one of the restrictive set of bi-splits.

16. The apparatus of claim 15 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes at least one of

the quad split, and

a bi-split that splits the predetermined block into two subblocks along a split line that is parallel to the picture boundary's position in the predetermined block and which split line is at least one of collocated to the picture boundary and centered inside the predetermined block.

17. The apparatus of claim 16 , wherein, if a bi-split from the reduced set is applied and the number of consecutive bi-splits is restricted to a predetermined maximum number of consecutive bi-splits, the apparatus is configured to not count a consecutive bi-split if said consecutive bi-split is applied over a picture boundary.

18. The apparatus of claim 15 , wherein the apparatus is configured to, for reducing the available set of split modes to the reduced set of one or more split modes, select from the available set of split modes the quad split only if the predetermined block extends beyond a corner of the picture.

19. A method for encoding a picture, comprising:

partitioning the picture into leaf blocks using recursive multi-tree partitioning,

block-based encoding the picture into a data stream using the partitioning of the picture into the leaf blocks,

wherein the method further comprises, in partitioning the picture into the leaf blocks,

for a predetermined block that corresponds to a predetermined tree level of the multi-tree partitioning and which extends beyond a boundary of the picture, reducing an available set of split modes for splitting the predetermined block depending on a position at which the picture boundary crosses the predetermined block in order to acquire a reduced set of one or more split modes, wherein

if a cardinality of the reduced set is one, the method comprises applying the split mode of the reduced set for splitting the predetermined block, and

if a cardinality of the reduced set is greater than one, the method comprising selecting one of the split modes of the reduced set and applying the selected one of the split modes for splitting the predetermined block and signaling the selection in the data stream.

20. A method for decoding a picture, comprising:

partitioning the picture into leaf blocks using recursive multi-tree partitioning,

block-based decoding the picture from a data stream using the partitioning of the picture into leaf blocks,

wherein the method further comprises, in partitioning the picture into the leaf blocks,

for a predetermined block, which corresponds to a predetermined tree level of the multi-tree partitioning and which extends beyond a boundary of the picture, reducing an available set of split modes for splitting the predetermined block depending on a position at which the picture boundary crosses the predetermined block in order to acquire a reduced set of one or more split modes, wherein

if a cardinality of the reduced set is one, the method comprises applying the split mode of the reduced set for splitting the predetermined block, and

if a cardinality of the reduced set is greater than one, the method further comprising selecting one of the split modes of the reduced set and applying the selected one of the split modes for splitting the predetermined block according to a signalization in the data stream.

21. A non-transitory digital storage medium having stored thereon a computer program for performing a method for encoding a picture, comprising:

partitioning the picture into leaf blocks using recursive multi-tree partitioning,

block-based encoding the picture into a data stream using the partitioning of the picture into the leaf blocks,

wherein the method further comprises, in partitioning the picture into the leaf blocks,

for a predetermined block that corresponds to a predetermined tree level of the multi-tree partitioning and which extends beyond a boundary of the picture, reducing an available set of split modes for splitting the predetermined block depending on a position at which the picture boundary crosses the predetermined block in order to acquire a reduced set of one or more split modes, wherein

if a cardinality of the reduced set is one, the method comprises applying the split mode of the reduced set for splitting the predetermined block, and

if a cardinality of the reduced set is greater than one, the method comprising selecting one of the split modes of the reduced set and applying the selected one of the split modes for splitting the predetermined block and signaling the selection in the data stream,

when said computer program is run by a computer.

22. A non-transitory digital storage medium having stored thereon a computer program for performing a method for decoding a picture, comprising:

partitioning the picture into leaf blocks using recursive multi-tree partitioning,

block-based decoding the picture from a data stream using the partitioning of the picture into leaf blocks,

wherein the method further comprises, in partitioning the picture into the leaf blocks,

for a predetermined block, which corresponds to a predetermined tree level of the multi-tree partitioning and which extends beyond a boundary of the picture, reducing an available set of split modes for splitting the predetermined block depending on a position at which the picture boundary crosses the predetermined block in order to acquire a reduced set of one or more split modes, wherein

if a cardinality of the reduced set is one, the method further comprises applying the split mode of the reduced set for splitting the predetermined block, and

if a cardinality of the reduced set is greater than one, the method further comprising selecting one of the split modes of the reduced set and applying the selected one of the split modes for splitting the predetermined block according to a signalization in the data stream,

when said computer program is run by a computer.

23. A data stream acquired by the method for encoding a picture according to claim 19 .

24. A data stream acquired by the method for decoding a picture according to claim 20 .