On boundary forced partition

Abstract

An apparatus and method of partitioning of an image or an image slice is described herein. In particular, on an image processing apparatus, the image or image slice is split into an integer number of coding tree units in both vertical and horizontal directions. The remaining boundary portion is then at least partly forced-split so that the deepest partitioning level is a result of binary partitioning, i.e. includes a coding unit which is longer on one side than on the other side. The longer side is parallel or concurrent to the image or image slice boundary.

1 . An apparatus for splitting a portion of a picture into coding units, the apparatus including a processing circuitry configured to:
 subdivide the portion of the picture into an integer number of coding tree units (CTUs) with a predetermined size and an incomplete coding tree unit at a picture boundary, and   partition the incomplete coding tree unit hierarchically into coding units (CUs) using forced quad-tree (QT) partitioning, and forced binary-tree (BT) partitioning for a coding unit resulting from the forced quad-tree partitioning.   
     
     
         2 . The apparatus according to  claim 1 , wherein the processing circuitry is configured to partition the incomplete coding tree unit by forced binary tree partitioning at least in the deepest partitioning level. 
     
     
         3 . The apparatus according to  claim 1 , wherein the processing circuitry is configured to:
 partition the incomplete coding tree unit by forced quad-tree partitioning in N shallowest levels, N being an integer larger than zero and smaller than the number of partitioning hierarchy levels; and   partition the incomplete coding tree unit by forced binary tree partitioning in the remaining partitioning hierarchy levels.   
     
     
         4 . The apparatus according to  claim 1 , wherein the processing circuitry, in operation, partitions the coding unit resulting from the forced quad-tree partitioning by forced binary partitioning until the deepest-level coding unit remains entirely within the picture. 
     
     
         5 . The apparatus according to  claim 1 , wherein the processing circuitry, in operation, partitions the CU resulting from the forced quad-tree partitioning by forced binary tree partitioning in either horizontal or vertical direction. 
     
     
         6 . An apparatus for encoding a picture of a video sequence comprising:
 the apparatus for splitting a portion of a picture into coding units according to  claim 1 ;   an image coding unit configured to encode the coding units; and   a bitstream forming unit configured to generate a bitstream including the coded coding units and a partitioning information indicating how the coding tree units are partitioned.   
     
     
         7 . The encoder according to  claim 6 , further comprising a rate-distortion optimization unit configured to determine hierarchical partitioning the incomplete coding tree unit according to rate-distortion optimization for a coding unit of the incomplete coding tree unit located inside the picture. 
     
     
         8 . An apparatus for decoding a picture of a video sequence comprising:
 the apparatus for determining splitting of a portion of a picture to be decoded into coding units according to  claim 1 ;   a bitstream parser for parsing a bitstream including the coded coding units and a partitioning information indicating how the coding tree units are partitioned and based on the determined splitting of the image portion;   an image decoding unit for decoding the coded coding units.   
     
     
         9 . The apparatus according to  claim 8 , wherein the splitting of the incomplete coding tree unit into coding units is a predefined splitting and the partitioning information does not relate to the forced splitting of the incomplete coding tree unit. 
     
     
         10 . The apparatus according to  claim 6 , wherein
 the processing circuitry is configured to partition the incomplete coding tree unit by forced quad-tree partitioning in N shallowest levels, N being an integer larger than zero and smaller than the number of partitioning hierarchy levels; and partition the incomplete coding tree unit by forced binary tree partitioning in the remaining partitioning hierarchy levels; and   the partitioning information includes N or N is derived based on a type of prediction applied to encode the picture being processed.   
     
     
         11 . A method for splitting a portion of a picture into coding units including:
 subdividing the portion of the picture into an integer number of coding tree units with a predetermined size and an incomplete coding tree unit at a picture boundary, and   partitioning the incomplete coding tree unit hierarchically into coding units using forced quad-tree partitioning, and forced binary-tree partitioning for a coding unit (CU) resulting from the forced quad-tree partitioning.   
     
     
         12 . The method according to  claim 11 , the partitioning of the incomplete coding tree unit further comprising the steps of:
 starting with a current partitioning level being the shallowest partitioning level,   sequentially splitting the incomplete coding tree unit to coding units of the current partitioning level, until a coding unit of the current partitioning level falls entirely within the picture;   as soon as the coding unit of the current partitioning level does not fall within the picture, increase the partitioning level and further partition said coding unit, wherein a forced quad-tree partitioning is used for N shallowest partitioning levels and forced binary tree partitioning is used otherwise, N being an integer larger than zero and smaller than the number of partitioning hierarchy levels.   
     
     
         13 . A non-transitory computer readable medium storing instructions which, when executed by a processor, cause the processor to execute a method for splitting a portion of a picture into coding units including:
 subdividing the portion of the picture into an integer number of coding tree units with a predetermined size and an incomplete coding tree unit at a picture boundary, and   partitioning the incomplete coding tree unit hierarchically into coding units using forced quad-tree partitioning, and forced binary partitioning for a coding unit resulting from the forced quad-tree partitioning.