Multi-Level Significance Maps for Encoding and Decoding

1 . An encoding apparatus comprising at least one processor, the at least one processor configured to:

for a first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

encode, into a bitstream, a significant-coefficient group flag (significant-CG flag) indicating that the first block has at least one non-zero coefficient;

encode, for each position in the first block other than a (0,0) position in the first block, a significant-coefficient flag into the bitstream, the significant-coefficient flag indicating whether a coefficient at the respective position in the first block is non-zero;

determine whether any coefficient not at the (0,0) position is non-zero;

in response to a determination that at least one coefficient not at the (0,0) position is non-zero, encode, into the bitstream, a significant-coefficient flag indicating whether a coefficient at the (0,0) position is non-zero; and

in response to a determination that all coefficients not at the (0,0) position are zero, not encode a significant-coefficient flag for the (0,0) position; and

for a second block within the transform unit, that contains the position of the DC coefficient in the transform unit:

not encode a significant-CG flag; and

encode, for each position in the second block, a significant-coefficient flag into the bitstream, the significant-coefficient flag indicating whether a coefficient at the respective position in the second block is non-zero.

2 . The encoding apparatus of claim 1 , the at least one processor further configured to:

for the first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

determine whether any coefficient not at the (0,0) position is non-zero by checking the respective significant-coefficient flag.

3 . The encoding apparatus of claim 1 , the at least one processor further configured to:

for a third block within the transform unit, that contains a position of a last non-zero coefficient in the transform unit:

not encode a significant-CG flag;

encode, for at least one position in the third block that is not the position of the last non-zero coefficient in the transform unit, a significant-coefficient flag into the bitstream, the significant-coefficient flag indicating whether a coefficient at the respective position in the third block is non-zero; and

not encode a significant-coefficient flag for the position of the last non-zero coefficient in the transform unit.

4 . A video encoding method comprising:

for a first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

encoding, into a bitstream, a significant-coefficient group flag (significant-CG flag) indicating that the first block has at least one non-zero coefficient;

encoding, for each position in the first block other than a (0,0) position in the first block, a significant-coefficient flag into the bitstream, the significant-coefficient flag indicating whether a coefficient at the respective position in the first block is non-zero;

determining whether any coefficient not at the (0,0) position is non-zero;

in response to a determination that at least one coefficient not at the (0,0) position is non-zero, encoding, into the bitstream, a significant-coefficient flag indicating whether a coefficient at the (0,0) position is non-zero; and

in response to a determination that all coefficients not at the (0,0) position are zero, not encoding a significant-coefficient flag for the (0,0) position; and

for a second block within the transform unit, that contains the position of the DC coefficient in the transform unit:

not encoding a significant-CG flag; and

encoding, for each position in the second block, a significant-coefficient flag into the bitstream, the significant-coefficient flag indicating whether a coefficient at the respective position in the second block is non-zero.

5 . The video encoding method of claim 4 , further comprising:

for the first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

determining whether any coefficient not at the (0,0) position is non-zero by checking the respective significant-coefficient flag.

6 . The video encoding method of claim 4 , further comprising:

for a third block within the transform unit, that contains a position of a last non-zero coefficient in the transform unit:

not encoding a significant-CG flag;

encoding, for at least one position in the third block that is not the position of the last non-zero coefficient in the transform unit, a significant-coefficient flag into the bitstream, the significant-coefficient flag indicating whether a coefficient at the respective position in the third block is non-zero; and

not encoding a significant-coefficient flag for the position of the last non-zero coefficient in the transform unit.

7 . A decoding apparatus comprising at least one processor, the at least one processor configured to:

for a first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

decode a significant-coefficient group flag (significant-CG flag) indicating that the first block has at least one non-zero coefficient;

decode, for each position in the first block other than a (0,0) position in the first block, a significant-coefficient flag indicating whether a coefficient at the respective position in the first block is non-zero;

determine whether any coefficient not at the (0,0) position is non-zero;

in response to a determination that at least one coefficient not at the (0,0) position is non-zero, decode a significant-coefficient flag indicating whether a coefficient at the (0,0) position is non-zero; and

in response to a determination that all coefficients not at the (0,0) position are zero, not decode a significant-coefficient flag for the (0,0) position and infer that a coefficient at the (0,0) position is non-zero; and

for a second block within the transform unit, that contains the position of the DC coefficient in the transform unit:

not decode a significant-CG flag; and

decode, for each position in the second block, a significant-coefficient flag indicating whether a coefficient at the respective position in the second block is non-zero.

8 . The decoding apparatus of claim 7 , the at least one processor further configured to:

for the first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

determine whether any coefficient not at the (0,0) position is non-zero by checking the respective significant-coefficient flag.

9 . The decoding apparatus of claim 7 , the at least one processor further configured to:

for a third block within the transform unit, that contains a position of a last non-zero coefficient in the transform unit:

not decode a significant-CG flag;

decode, for at least one position in the third block that is not the position of the last non-zero coefficient in the transform unit, a significant-coefficient flag, the significant-coefficient flag indicating whether a coefficient at the respective position in the third block is non-zero; and

not decode a significant-coefficient flag for the position of the last non-zero coefficient in the transform unit.

10 . A video decoding method comprising:

for a first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

decoding a significant-coefficient group flag (significant-CG flag) indicating that the first block has at least one non-zero coefficient;

decoding, for each position in the first block other than a (0,0) position in the first block, a significant-coefficient flag indicating whether a coefficient at the respective position in the first block is non-zero;

determining whether any coefficient not at the (0,0) position is non-zero;

in response to a determination that at least one coefficient not at the (0,0) position is non-zero, decoding a significant-coefficient flag indicating whether a coefficient at the (0,0) position is non-zero; and

in response to a determination that all coefficients not at the (0,0) position are zero, not decoding a significant-coefficient flag for the (0,0) position, and inferring that a coefficient at the (0,0) position is non-zero; and

for a second block within the transform unit, that contains the position of the DC coefficient in the transform unit:

not decoding a significant-CG flag; and

decoding, for each position in the second block, a significant-coefficient flag indicating whether a coefficient at the respective position in the second block is non-zero.

11 . The decoding method of claim 10 , further comprising:

for the first block within a transform unit, that does not contain a position of a DC coefficient in the transform unit:

determining whether any coefficient not at the (0,0) position is non-zero by checking the respective significant-coefficient flag.

12 . The decoding method of claim 10 , further comprising:

for a third block within the transform unit, that contains a position of a last non-zero coefficient in the transform unit:

not decoding a significant-CG flag;

decoding, for at least one position in the third block that is not the position of the last non-zero coefficient in the transform unit, a significant-coefficient flag, the significant-coefficient flag indicating whether a coefficient at the respective position in the third block is non-zero; and

not decoding a significant-coefficient flag for the position of the last non-zero coefficient in the transform unit.

13 . A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors, cause a video processing apparatus to:

generate a coded video bitstream,

wherein the coded video bitstream includes, for a first block within a transform unit that does not contain a position of a DC coefficient in the transform unit, a significant-coefficient group flag (significant-CG flag) indicating that the first block has at least one non-zero coefficient, wherein for each position in the first block other than a (0,0) position in the first block, the coded video bitstream includes a significant-coefficient flag, the significant-coefficient flag indicating whether a coefficient at the respective position in the first block is non-zero, wherein the coded video bitstream includes a significant-coefficient flag indicating whether a coefficient at the (0,0) position is non-zero for the first block, wherein the coded video bitstream does not include a significant-coefficient flag for the (0,0) position for the first block;

wherein the coded video bitstream includes, for a second block within the transform unit that contains the position of the DC coefficient in the transform unit and for each position in the second block, a significant-coefficient flag indicates whether a coefficient at the respective position in the second block is non-zero, wherein the coded video bitstream does not include a significant-CG flag for the second block; and

transmit the coded video bitstream toward a decoding device.

14 . The non-transitory computer-readable storage medium of claim 14 , wherein the coded video bitstream includes, for a third block within the transform unit that does not include a significant-CG flag and for at least one position in the third block that is not the position of the last non-zero coefficient in the transform unit, a significant-coefficient flag, wherein the significant-coefficient flag indicates whether a coefficient at the respective position in the third block is non-zero, and wherein the coded vide bitstream does not include a significant-coefficient flag for the position of the last non-zero coefficient in the transform unit.

15 . A non-transitory computer-readable storage medium storing instructions that, when executed by one or more processors, cause a video processing apparatus to:

obtain a decoded video bitstream,

wherein the decoded video bitstream includes, for a first block within a transform unit that does not contain a position of a DC coefficient in the transform unit, a significant-coefficient group flag (significant-CG flag) indicating that the first block has at least one non-zero coefficient, wherein for each position in the first block other than a (0,0) position in the first block, the decoded video bitstream includes a significant-coefficient flag indicating whether a coefficient at the respective position in the first block is non-zero, wherein the decoded video bitstream includes a significant-coefficient flag indicating whether a coefficient at the (0,0) position is non-zero for the first block, wherein the decoded video bitstream does not include a significant-coefficient flag for the (0,0) position for the first block;

wherein the decoded video bitstream includes, for a second block within the transform unit that contains the position of the DC coefficient in the transform unit, a significant-coefficient flag indicating whether a coefficient at the respective position in the second block is non-zero, and wherein the decoded video bitstream does not include, for the second block, a significant-GC flag; and

generate a picture based on the coded video bitstream.

16 . The non-transitory computer-readable storage medium of claim 16 , wherein the decoded video bitstream includes, for a third block within the transform unit that does not include a significant-CG flag for the third block and for at least one position in the third block that is not the position of the last non-zero coefficient in the transform unit, a significant-coefficient flag, the significant-coefficient flag indicating whether a coefficient at the respective position in the third block is non-zero.