Method of reducing context models for entropy coding of transform coefficient significant flag

A method of video encoding performed in a video encoder, the method comprising:

• determining, for each context model region from a plurality of context model regions, an output of a monotonically non-decreasing function performed on a sum of a group of partially reconstructed transform coefficients and a number of context models associated with a respective context model region;
• determining a context model index based on the output of the monotonically non-decreasing function of each context model region;
• selecting, for at least one syntax of a current transform coefficient of a transform block in a current picture, a context model from a plurality of context models based on the determined context model index;
• and
• generating a coded video bitstream including a current picture and the at least one syntax element that corresponds to transform coefficients of a transform block in the current picture.

A video encoder for video encoding, comprising:

• processing circuitry configured to:
• determine an offset value based on an output of a monotonically non-decreasing function performed on a sum of a group of partially reconstructed transform coefficients,
• determine a context model index based on a sum of the determined offset value and a base value,
• select, for at least one syntax of a current transform coefficient of a transform block in a current picture, a context model from a plurality of context models based on the determined context model index, and
• generate a coded video bitstream including the current picture and the at least one syntax element that corresponds to transform coefficients of the transform block in the current picture,
• wherein one of the base value and the offset value is determined based on a number of context models included in the plurality of context models.

A video encoder apparatus for video decoding, comprising:

• processing circuitry configured to:
• determine, for each context model region from a plurality of context model regions, an output of a monotonically non-decreasing function performed on a sum of a group of partially reconstructed transform coefficients and a number of context models associated with a respective context model region,
• determine a context model index based on the output of the monotonically non-decreasing function of each context model region,
• select, for at least one syntax of a current transform coefficient of a transform block in a current picture, a context model from a plurality of context models based on the determined context model index, and
• generate a coded video bitstream including a current picture and the at least one syntax element that corresponds to transform coefficients of a transform block in the current picture.