Method, apparatus and system for encoding and decoding the transform units of a coding unit

A method of encoding a transform unit containing chroma residual samples to a video bitstream, the transform unit containing a plurality of chroma residual coefficient arrays associated with a single chroma channel in a 4:2:2 chroma format, the method comprising:

• encoding a plurality of coded block flag values to the video bitstream for a single chroma channel of the transform unit, wherein the transform unit has a plurality of chroma residual coefficient arrays for a single colour channel and each coded block flag value of the plurality of coded block flag values corresponds to one chroma residual coefficient array of the chroma residual coefficient arrays;
• selecting a square forward transform for the chroma residual coefficient arrays, the square forward transform being selected from a predetermined set of square forward transforms according to a transform size of the transform unit;
• applying the selected square forward transform to each of the chroma residual coefficient arrays to produce the chroma residual samples for the chroma channel of the transform unit;
• and
• encoding to the video bitstream each of the plurality of chroma residual coefficient arrays according to a corresponding coded block flag value of the plurality of coding block flag values.

A video decoder for decoding a transform unit containing chroma residual samples from a video bitstream, the transform unit containing a plurality of chroma residual coefficient arrays associated with a single chroma channel in a 4:2:2 chroma format, the decoder comprising:

• a first decoder to decoding a plurality of coded block flag values from the video bitstream for a single chroma channel of the transform unit, wherein the transform unit has a plurality of chroma residual coefficient arrays for a single colour channel and each coded block flag value of the plurality of coded block flag values corresponds to one chroma residual coefficient array of the chroma residual coefficient arrays;
• a second decoder to decode from the video bitstream each of a plurality of chroma residual coefficient arrays according to a corresponding coded block flag value of the plurality of coding block flag values;
• a selector to select a square inverse transform for the decoded chroma residual coefficient arrays, the square inverse transform being selected from a predetermined set of square inverse transforms according to a determined transform size of the transform unit;
• and
• an applicator to apply the selected square inverse transform to each of the decoded chroma residual coefficient arrays to produce the chroma residual samples for the chroma channel of the transform unit.

A non-transitory computer readable storage medium having a program recorded thereon, the program being executable by a processor to decode a transform unit containing chroma residual samples from a video bitstream, the transform unit containing a plurality of chroma residual coefficient arrays associated with a single chroma channel in a 4:2:2 chroma format, the program comprising:

• code for decoding a plurality of coded block flag values from the video bitstream for a single chroma channel of the transform unit, wherein the transform unit has a plurality of chroma residual coefficient arrays for a single colour channel and each coded block flag value of the plurality of coded block flag values corresponds to one chroma residual coefficient array of the chroma residual coefficient arrays;
• code for decoding from the video bitstream each of a plurality of chroma residual coefficient arrays according to a corresponding coded block flag value of the plurality of coding block flag values;
• code for selecting a square inverse transform for the decoded chroma residual coefficient arrays, the square inverse transform being selected from a predetermined set of square inverse transforms according to a transform size of the transform unit;
• and
• code for applying the selected square inverse transform to each of the decoded chroma residual coefficient arrays to produce the chroma residual samples for the chroma channel of the transform unit.

A video encoder to encode a transform unit containing chroma residual samples to a video bitstream, the transform unit containing a plurality of chroma residual coefficient arrays associated with a single chroma channel in a 4:2:2 chroma format, the encoder comprising:

• a first encoder to encode a plurality of coded block flag values to the video bitstream for a single chroma channel of the transform unit, wherein the transform unit has a plurality of chroma residual coefficient arrays for a single colour channel and each coded block flag value of the plurality of coded block flag values corresponds to one chroma residual coefficient array of the chroma residual coefficient arrays;
• a selector to select a square forward transform for the chroma residual coefficient arrays, the square forward transform being selected from a predetermined set of square forward transforms according to a transform size of the transform unit;
• an applicator to apply the selected square forward transform to each of the chroma residual coefficient arrays to produce the chroma residual samples for the chroma channel of the transform unit;
• and
• a second encoder to encode to the video bitstream each of the plurality of chroma residual coefficient arrays according to a corresponding coded block flag value of the plurality of coding block flag values.

A non-transitory computer readable storage medium having a program recorded thereon, the program being executable by a processor to encode a transform unit containing chroma residual samples to a video bitstream, the transform unit containing a plurality of chroma residual coefficient arrays associated with a single chroma channel in a 4:2:2 chroma format, the program comprising:

• code for encoding a plurality of coded block flag values to the video bitstream for a single chroma channel of the transform unit, wherein the transform unit has a plurality of chroma residual coefficient arrays for a single colour channel and each coded block flag value of the plurality of coded block flag values corresponds to one chroma residual coefficient array of the chroma residual coefficient arrays;
• code for selecting a square forward transform for the chroma residual coefficient arrays, the square forward transform being selected from a predetermined set of square forward transforms according to a transform size of the transform unit;
• code for applying the selected square forward transform to each of the chroma residual coefficient arrays to produce the chroma residual samples for the chroma channel of the transform unit;
• and
• code for encoding to the video bitstream each of the plurality of chroma residual coefficient arrays according to a corresponding coded block flag value of the plurality of coding block flag values.