An apparatus for splitting a portion of a picture into coding units, the apparatus including a processing circuitry, wherein the processing circuitry is configured to: subdivide the image portion into an integer number of coding tree units with a predetermined size and a boundary coding tree unit located on a picture boundary, wherein the boundary coding tree unit comprises a part located inside the picture with a size smaller than the predetermined size in at least a first direction, which is either a horizontal or vertical direction, and a part located outside the picture, partition the boundary coding tree unit by quad-tree splitting in N shallowest levels, N being an integer larger than zero and smaller than the number of partitioning hierarchy levels; partition hierarchically a boundary coding unit of the boundary coding tree unit resulting from the quad-tree splitting using forced binary tree partitioning into coding units including a deepest-level coding unit with different sizes in respective horizontal and vertical directions, the deepest-level coding unit being smaller in the first direction, wherein the forced binary tree partitioning comprises: when the boundary coding unit is located on the bottom boundary of the picture, partition the boundary coding unit recursively using horizontal binary tree partitioning for partitioning boundary coding units of the boundary coding unit until the deepest-level coding unit of the forced binary tree partitioning is located entirely within the picture, wherein the first direction is the vertical direction, and when the boundary coding unit is located on the right boundary of the picture, partition the boundary coding unit recursively using vertical binary partitioning for partitioning boundary coding units of the boundary coding unit until the deepest-level coding unit of the forced binary tree partitioning is located entirely within the picture, wherein the first direction is the horizontal direction; and wherein the forced binary tree partitioning is a predefined partitioning and no partitioning flag to indicate the partitioning of the forced partitioned boundary coding unit is signaled in the bitstream. subdivide the image portion into an integer number of coding tree units with a predetermined size and a boundary coding tree unit located on a picture boundary, wherein the boundary coding tree unit comprises a part located inside the picture with a size smaller than the predetermined size in at least a first direction, which is either a horizontal or vertical direction, and a part located outside the picture, partition the boundary coding tree unit by quad-tree splitting in N shallowest levels, N being an integer larger than zero and smaller than the number of partitioning hierarchy levels; partition hierarchically a boundary coding unit of the boundary coding tree unit resulting from the quad-tree splitting using forced binary tree partitioning into coding units including a deepest-level coding unit with different sizes in respective horizontal and vertical directions, the deepest-level coding unit being smaller in the first direction, wherein the forced binary tree partitioning comprises: when the boundary coding unit is located on the bottom boundary of the picture, partition the boundary coding unit recursively using horizontal binary tree partitioning for partitioning boundary coding units of the boundary coding unit until the deepest-level coding unit of the forced binary tree partitioning is located entirely within the picture, wherein the first direction is the vertical direction, and when the boundary coding unit is located on the right boundary of the picture, partition the boundary coding unit recursively using vertical binary partitioning for partitioning boundary coding units of the boundary coding unit until the deepest-level coding unit of the forced binary tree partitioning is located entirely within the picture, wherein the first direction is the horizontal direction; and wherein the forced binary tree partitioning is a predefined partitioning and no partitioning flag to indicate the partitioning of the forced partitioned boundary coding unit is signaled in the bitstream. when the boundary coding unit is located on the bottom boundary of the picture, partition the boundary coding unit recursively using horizontal binary tree partitioning for partitioning boundary coding units of the boundary coding unit until the deepest-level coding unit of the forced binary tree partitioning is located entirely within the picture, wherein the first direction is the vertical direction, and when the boundary coding unit is located on the right boundary of the picture, partition the boundary coding unit recursively using vertical binary partitioning for partitioning boundary coding units of the boundary coding unit until the deepest-level coding unit of the forced binary tree partitioning is located entirely within the picture, wherein the first direction is the horizontal direction; and wherein the forced binary tree partitioning is a predefined partitioning and no partitioning flag to indicate the partitioning of the forced partitioned boundary coding unit is signaled in the bitstream.