Coding of transform coefficients for video coding

An apparatus configured to code a plurality of transform coefficients associated with residual video data of a transform block in a video coding process, the apparatus comprising:

• a memory configured to store the plurality of transform coefficients;
• and a video coding processor configured to:
• code a significant coefficient flag for each transform coefficient of the plurality of transform coefficients according to a scan order in a first scan pass of the plurality of transform coefficients, the plurality of transform coefficients being arranged in a two-dimensional array, each significant coefficient flag indicating whether or not a corresponding transform coefficient of the plurality of transform coefficients is a significant coefficient having an absolute value greater than zero, wherein the scan order includes a diagonal scan pattern and an inverse scan direction proceeding from higher frequency transform coefficients of the plurality of transform coefficients to lower frequency transform coefficients of the plurality of transform coefficients;
• and
• code information indicating levels of the plurality of transform coefficients according to the scan order in a second scan pass of the plurality of transform coefficients, the plurality of transform coefficients being arranged in the two-dimensional array, and the scan order including the diagonal scan pattern and the inverse scan direction,
• wherein, to code the significant coefficient flag for each transform coefficient of the plurality of transform coefficients, the video coding processor is configured to:
• arrange the plurality of transform coefficients into at least a first region of the transform block and a second region of the transform block, the first region of the transform block containing at least a DC component of the plurality of transform coefficients,
• derive a first set of contexts for the first region of the transform block which includes one or more probability models, the first set of contexts being derived using context derivation criteria, derive a second set of contexts for the second region of the transform block including one or more probability models, the second set of contexts being derived using the context derivation criteria,
• entropy code a respective significant coefficient flag for each transform coefficient of the plurality of transform coefficients in the first region of the transform block according to the first set of contexts, and
• entropy code a respective significant coefficient flag for each transform coefficient of the plurality of transform coefficients in the second region of the transform block according to the second set of contexts.

A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors of a device for coding a plurality of transform coefficients associated with residual video data of a transform block in a video coding process to:

• code a significant coefficient flag for each transform coefficient of the plurality of transform coefficients according to a scan order in a first scan pass of the plurality of transform coefficients, the plurality of transform coefficients being arranged in a two-dimensional array, each significant coefficient flag indicating whether or not a corresponding transform coefficient of the plurality of transform coefficients is a significant coefficient having an absolute value greater than zero,
• wherein the scan order includes a diagonal scan pattern and an inverse scan direction proceeding from higher frequency transform coefficients of the plurality of transform coefficients to lower frequency transform coefficients of the plurality of transform coefficients;
• and
• code information indicating levels of the plurality of transform coefficients according to the scan order in a second scan pass of the plurality of transform coefficients, the plurality of transform coefficients being arranged in the two-dimensional array, and the scan order including the diagonal scan pattern and the inverse scan direction,
• wherein, to code the significant coefficient flag for each transform coefficient of the plurality of transform coefficients, the non-transitory computer-readable storage medium further has stored thereon instructions that, when executed, cause one or more processors of the device to:
• arrange the plurality of transform coefficients into at least a first region of the transform block and a second region of the transform block, the first region of the transform block containing at least a DC component of the plurality of transform coefficients,
• derive a first set of contexts for the first region of the transform block which includes one or more probability models, the first set of contexts being derived using context derivation criteria,
• deriving a second set of contexts for the second region of the transform block including one or more probability models, the second set of contexts being derived using the context derivation criteria,
• entropy code a respective significant coefficient flag for each transform coefficient of the plurality of transform coefficients in the first region of the transform block according to the first set of contexts, and
• entropy code a respective significant coefficient flag for each transform coefficient of the plurality of transform coefficients in the second region of the transform block according to the second set of contexts.