Transform skip mode

A method of encoding video data, the method comprising:

• determining a sub-sampling format for a chroma transform block (TB);
• based on the sub-sampling format for the chroma TB, identifying one or more corresponding luma TBs;
• determining if a size of a coding unit comprising the chroma TB is equal to a smallest enabled size for coding units;
• in response to determining that the size of the coding unit is equal to the smallest enabled size, generating, for each of the one or more corresponding luma TBs, a flag indicating if the corresponding TB is coded using a transform skip mode;
• and
• based on a number of the one or more corresponding luma TBs coded using the transform skip mode being greater than or equal to a threshold value, encoding the chroma TB using the transform skip mode without generating a syntax element indicating the chroma TB is coded using the transform skip mode.

A device for coding video data, the device comprising:

• a memory configured to store video data;
• and
• a video coder configured to:
• determine a sub-sampling format for a chroma transform block (TB) of the video data;
• based on the sub-sampling format for the chroma TB, identify one or more corresponding luma TBs;
• determine if a size of a coding unit comprising the chroma TB is equal to a smallest enabled size for coding units;
• in response to determining that the size of the coding unit is equal to the smallest enabled size, code, for each of the one or more corresponding luma TBs, a flag indicating if the corresponding luma TB is coded using a transform skip mode;
• and
• based on a number of the one or more corresponding luma TBs coded using the transform skip mode being greater than or equal to a threshold value, determine that the chroma TB is coded in the transform skip mode.

An apparatus for coding video data, the apparatus comprising:

• means for determining a sub-sampling format for a chroma transform block (TB);
• means for identifying one or more corresponding luma TBs based on the sub-sampling format for the chroma TB;
• means for determining if a size of a coding unit comprising the chroma TB is equal to a smallest enabled size for coding units;
• means for coding, in response to determining that the size of the coding unit is equal to the smallest enabled size, for each of the one or more corresponding luma TBs, a flag indicating if the corresponding luma TB is coded using a transform skip mode;
• and
• means for determining that the chroma TB is coded in the transform skip mode based on a number of the one or more corresponding luma TBs coded using the transform skip mode being greater than or equal to a threshold value.

A computer readable storage medium storing instructions that when executed cause one or more processors to:

• determine a sub-sampling format for a chroma transform block (TB);
• identify one or more corresponding luma TBs based on the sub-sampling format for the chroma TB;
• determine if a size of a coding unit comprising the chroma TB is equal to a smallest enabled size for coding units;
• in response to determining that the size of the coding unit is equal to the smallest enabled size, code, for each of the one or more corresponding luma TBs, a flag indicating if the corresponding luma TB is coded using a transform skip mode;
• and
• determine that the chroma TB is coded in the transform skip mode based on a number of the one or more corresponding luma TBs coded using the transform skip mode being greater than or equal to a threshold value.