Method, apparatus and system for encoding and decoding a tree of blocks of video samples

A method of encoding blocks of a coding tree unit in an image, into a bitstream, the method comprising:

• determining a chroma format of the image from a plurality of chroma formats;
• determining luma split options for a luma channel of the coding tree unit according to a size of a region in the coding tree unit;
• determining chroma split options for chroma channels of the coding tree unit according to a size of a region in the coding tree unit, the chroma split options being capable of including a vertical ternary split and including a quad split, wherein a tree structure for the chroma channels of the coding tree unit is separate from a tree structure for the luma channel of the coding tree unit, and the vertical ternary split for a given region in the coding tree unit is not allowed in the chroma split options in a case where (a) a width of the given region is 16 samples in luma samples and (b) the determined chroma format is a 4:2:2 chroma format or a 4:2:0 chroma format;
• and
• encoding flags used for selecting one of the determined luma split options and one of the determined chroma split options.

A video decoding apparatus decoding blocks of a coding tree unit in an image from a bitstream, the video decoding apparatus comprising:

• a first determining unit configured to determine a chroma format of the image from a plurality of chroma formats;
• a second determining unit configured to determine luma split options for a luma channel of the coding tree unit according to a size of a region in the coding tree unit;
• a third determining unit configured to determine chroma split options for chroma channels of the coding tree unit according to a size of a region in the coding tree unit, the chroma split options being capable of including a vertical ternary split and including a quad split, wherein a tree structure for the chroma channels of the coding tree unit is separate from a tree structure for the luma channel of the coding tree unit, and the vertical ternary split for a given region in the coding tree unit is not allowed in the chroma split options in a case where (a) a width of the given region is 16 samples in luma samples and (b) the determined chroma format is a 4:2:2 chroma format or a 4:2:0 chroma format;
• and
• a decoding unit configured to decode flags from the bitstream to select one of the determined luma split options and one of the determined chroma split options.

An encoding apparatus encoding blocks of a coding tree unit in an image, the encoding apparatus comprising:

• a first determining unit configured to determine a chroma format of the image from a plurality of chroma formats;
• a second determining unit configured to determine luma split options for a luma channel of the coding tree unit according to a size of a region in the coding tree unit;
• a third determining unit configured to determine chroma split options for chroma channels of the coding tree unit according to a size of a region in the coding tree unit, the chroma split options being capable of including a vertical ternary split and including a quad split, wherein a tree structure for the chroma channels of the coding tree unit is separate from a tree structure for the luma channel of the coding tree unit, and the vertical ternary split for a given region in the coding tree unit is not allowed in the chroma split options in a case where (a) a width of the given region is 16 samples in luma samples and (b) the determined chroma format is a 4:2:2 chroma format or a 4:2:0 chroma format;
• and
• an encoding unit configured to encode flags used for selecting one of the determined luma split options and one of the determined chroma split options.

A non-transitory computer-readable storage medium storing a program for causing a computer to execute a method of decoding blocks of a coding tree unit in an image, from a bitstream, the method comprising:

• determining a chroma format of the image from a plurality of chroma formats;
• determining luma split options for a luma channel of the coding tree unit according to a size of a region in the coding tree unit;
• determining chroma split options for chroma channels of the coding tree unit according to a size of a region in the coding tree unit, the chroma split options being capable of including a vertical ternary split and including a quad split, wherein a tree structure for the chroma channels of the coding tree unit is separate from a tree structure for the luma channel of the coding tree unit, and the vertical ternary split for a given region in the coding tree unit is not allowed in the chroma split options in a case where (a) a width of the given region is 16 samples in luma samples and (b) the determined chroma format is a 4:2:2 chroma format or a 4:2:0 chroma format;
• and
• decoding flags from the bitstream to select one of the determined luma split options and one of the determined chroma split options.

A non-transitory computer-readable storage medium storing a program for causing a computer to execute a method of encoding blocks of a coding tree unit in an image, into a bitstream, the method comprising:

• determining a chroma format of the image from a plurality of chroma formats;
• determining luma split options for a luma channel of the coding tree unit according to a size of a region in the coding tree unit;
• determining chroma split options for chroma channels of the coding tree unit according to a size of a region in the coding tree unit, the chroma split options being capable of including a vertical ternary split and including a quad split, wherein a tree structure for the chroma channels of the coding tree unit is separate from a tree structure for the luma channel of the coding tree unit, and the vertical ternary split for a given region in the coding tree unit is not allowed in the chroma split options in a case where (a) a width of the given region is 16 samples in luma samples and (b) the determined chroma format is a 4:2:2 chroma format or a 4:2:0 chroma format;
• and
• encoding flags used for selecting one of the determined luma split options and one of the determined chroma split options.