Scalable video coding using subblock-based coding of transform coefficient blocks in the enhancement layer

1. A scalable video decoder comprising:

a first block-based decoding unit configured to decode, using a processor, a base layer residual signal of a base layer signal from a coded data stream; and

a second block-based decoding unit configured to reconstruct, using the processor, an enhancement layer signal, the second block-based decoding unit configured for decoding, using the processor, a transform coefficient block of transform coefficients representing an enhancement layer signal from the coded data stream, by:

selecting, for the transform coefficient block representing the enhancement layer signal, a subblock subdivision among a set of possible subblock subdivisions based on information including a spectral decomposition of a portion of the base layer residual signal or the base layer signal, wherein the transform coefficient block is subdivided into subblocks according to the selected subblock subdivision such that a dimension of at least one of the subblocks is longer along a first axis direction that is transverse to a second axis direction along which a spectral energy distribution of the spectral decomposition is narrower, and

traversing positions of the transform coefficients in units of the subblocks such that all positions within one subblock are traversed before proceeding to a next subblock in a subblock order defined among the subblocks,

wherein for a current subblock being traversed, the second block-based decoding unit is configured for:

decoding from the data stream a syntax element indicating as to whether the current subblock comprises any significant transform coefficient,

if the syntax element indicates that the current-subblock does not comprise any significant transform coefficient, setting the transform coefficients within the current-subblock equal to zero, and

if the syntax element indicates that the current-subblock comprises any significant transform coefficient, decoding from the data stream syntax elements indicating levels of the transform coefficients within the current subblock.

2. The scalable video decoder according to claim 1 , wherein the first block-based decoding unit comprises a first predictive decoder configured to decode the base layer signal from the coded data stream by prediction, the base layer residual signal representing a prediction residual of a prediction signal for the base layer signal.

3. The scalable video decoder according to claim 1 , wherein the second block-based decoding unit comprises:

an inverse transformer to perform an inverse transform on the transform coefficients of the transform coefficient block to obtain an enhancement layer residual signal representing a prediction residual of a prediction signal for the enhancement layer signal; and

a second predictive decoder configured to reconstruct the enhancement layer signal by spatially, temporally and/or inter-layer predicting the enhancement layer signal to obtain the prediction signal for the enhancement layer signal, and applying the enhancement layer residual signal to the prediction signal for the enhancement layer signal.

4. The scalable video decoder according to claim 1 , wherein the second block-based decoding unit is configured to select the subblock subdivision among the set of possible subblock subdivisions on the basis of the base layer signal.

5. The scalable video decoder according to claim 1 , wherein the second block-based decoding unit is configured to select the subblock subdivision among the set of possible subblock subdivisions by detecting edges within a portion of the base layer residual signal or the base layer signal, corresponding to the transform coefficient block and setting an extension of the subblocks of the selected subblock subdivision to be longer along a spatial frequency axis transverse to the edges.

6. The scalable video decoder according to claim 1 , wherein the second block-based decoding unit is configured to form the spectral decomposition of a portion of the base layer residual signal or the base layer signal by actually applying a transform onto the base layer residual signal or the base layer signal from spatial domain to frequency domain.

7. The scalable video decoder according to claim 1 , wherein the second block-based decoding unit is configured to form the spectral decomposition of a portion of the base layer residual signal or the base layer signal by combining and scaling transform coefficient blocks of the base layer residual signal, pertaining portions overlapping the portion of the base layer residual signal, corresponding to the transform coefficient block representing the enhancement layer signal.

8. A scalable video decoding method comprising:

decoding a base layer residual signal of a base layer signal from a coded data stream; and

reconstructing an enhancement layer signal comprising decoding a transform coefficient block of transform coefficients representing an enhancement layer signal from the coded data stream, by:

selecting, for the transform coefficient block representing the enhancement layer signal, a subblock subdivision among a set of possible subblock subdivisions based on information including a spectral decomposition of a portion of the base layer residual signal or the base layer signal, wherein the transform coefficient block is subdivided into subblocks according to the selected subblock subdivision such that a dimension of at least one of the subblocks is longer along a first axis direction that is transverse to a second axis direction along which a spectral energy distribution of the spectral decomposition is narrower, and

traversing positions of the transform coefficients in units of the subblocks such that all positions within one subblock are traversed before proceeding to a next subblock in a subblock order defined among the subblocks,

wherein for a current-subblock being traversed, wherein the traversing a current subblock comprises:

decoding from the data stream a syntax element indicating as to whether the current subblock comprises any significant transform coefficient,

if the syntax element indicates that the current subblock does not comprise any significant transform coefficient, setting the transform coefficients within the current-subblock equal to zero, and

if the syntax element indicates that the current subblock comprises any significant transform coefficient, decoding from the data stream syntax elements indicating levels of the transform coefficients within the current subblock.

9. A scalable video encoder comprising:

a first block-based encoding unit configured to encode, using a processor, a base layer residual signal of a base layer signal into a coded data stream; and

a second block-based encoding unit configured to encode, using the processor, an enhancement layer signal, the second block-based encoding unit configured for encoding, using the processor, a transform coefficient block of transform coefficients representing the enhancement layer signal from the coded data stream, by:

selecting, for the transform coefficient block representing the enhancement layer signal, a subblock subdivision among a set of possible subblock subdivisions based on information including a spectral decomposition of a portion of the base layer residual signal or the base layer signal, wherein the transform coefficient block is subdivided into subblocks according to the selected subblock subdivision such that a dimension of at least one of the subblocks is longer along a first axis direction that is transverse to a second axis direction along which a spectral energy distribution of the spectral decomposition is narrower, and

traversing positions of the transform coefficients in units of the subblocks such that all positions within one subblock are traversed before proceeding to a next subblock in a subblock order defined among the subblocks,

wherein for a current-subblock being traversed, the second block-based encoding unit is configured for:

encoding into the data stream a syntax element indicating as to whether the current subblock comprises any significant transform coefficient or not, and

if the syntax element indicates that the current subblock comprises any significant transform coefficient, encoding into the data stream syntax elements indicating levels of the transform coefficients within the current subblock.

10. A scalable video encoding method comprising:

encoding a base layer residual signal of a base layer signal into a coded data stream; and

encoding an enhancement layer signal comprising encoding a transform coefficient block of transform coefficients representing the enhancement layer signal from the coded data stream, by:

selecting, for the transform coefficient block representing the enhancement layer signal, a subblock subdivision among a set of possible subblock subdivisions based on information including a spectral decomposition of a portion of the base layer residual signal or the base layer signal, wherein the transform coefficient block is subdivided into subblocks according to the selected subblock subdivision such that a dimension of at least one of the subblocks is longer along a first axis direction that is transverse to a second axis direction along which a spectral energy distribution of the spectral decomposition is narrower, and

traversing positions of the transform coefficients in units of the subblocks such that all positions within one subblock are traversed before proceeding to a next subblock in a subblock order defined among the subblocks, wherein for a current-subblock being traversed, wherein the traversing a current subblock comprises:

encoding into the data stream a syntax element indicating as to whether the current subblock comprises any significant transform coefficient, and

if the syntax element indicates that the current subblock comprises any significant transform coefficient, encoding into the data stream syntax elements indicating levels of the transform coefficients within the current subblock.

11. A non-transitory computer readable medium including a computer program comprising a program code for performing, when running on a computer, a method according to claim 8 .

12. A non-transitory computer readable medium including a computer program comprising a program code for performing, when running on a computer, a method according to claim 10 .