Deblocking filter for sub-partition boundaries caused by intra sub-partition coding tool

A method for deblocking a sub-partitions boundary within a coding block during an image encoding or image decoding process and implemented by a coding device, wherein the coding block is coded in an intra prediction mode and the coding block is partitioned into sub-partitions by an intra sub-partition (ISP) and the sub-partitions including a first sub-partition and a second sub-partition, and wherein the first sub-partition is vertically adjacent to the second sub-partition, the method comprising:

• determining a first maximum filter length to be 1 for the first sub-partition, when a height of the first sub-partition is 4 samples or a height of the second sub-partition is 4 samples;
• and
• modifying, based at least in part upon the first maximum filter length, a value of up to one sample of the first sub-partition, wherein the up to one sample is obtained from a column of the first sub-partition that is perpendicular to the sub-partitions boundary between the first sub-partition and the second sub-partition and the up to one sample is adjacent to the sub-partitions boundary between the first sub-partition and the second sub-partition,
• wherein the sub-partitions boundary between the first sub-partition and the second sub-partition is caused by the intra sub-partition, and the sub-partitions boundary between the first sub-partition and the second sub-partition is an internal boundary.

A non-transitory computer-readable medium carrying programming instructions which, when executed by a computing device, cause the computing device to perform operations for deblocking a sub-partitions boundary within a coding block in image encoding or image decoding process, wherein the coding block is coded in an intra prediction mode and the coding block is partitioned into sub-partitions by an intra sub-partition (ISP) and the sub-partitions including a first sub-partition and a second sub-partition, wherein the first sub-partition is vertically adjacent to the second sub-partition, and wherein the operations include:

• determining a first maximum filter length to be 1 for the first sub-partition, when a height of the first sub-partition is 4 samples or a height of the second sub-partition is 4 samples;
• and
• modifying, based on the first maximum filter length, a value of up to one sample of the first sub-partition, wherein the value of the up to one sample is obtained from a column of the first sub-partition that is perpendicular to the sub-partitions boundary between the first sub-partition and the second sub-partition and the up to one sample is adjacent to the sub-partitions boundary between the first sub-partition and the second sub-partition,
• wherein the sub-partitions boundary between the first sub-partition and the second sub-partition is caused by the intra sub-partition, and the sub-partitions boundary between the first sub-partition and the second sub-partition is an internal boundary.