Modified coding for transform skipping
Methods and devices for modified coding of blocks of residuals in the case of transform skipping. To better align the data with assumptions upon which the entropy coding scheme is based, the block of residual data is permuted at the encoder prior to entropy coding. The block of reconstructed data is then inverse permuted at the decoder to recover the reconstructed block of residuals. The permutation may include 180 rotation of the block, which may be of particular benefit in the case of intra-coded residuals.
1. A method of decoding a coding unit from a bitstream, the method comprising:
decoding a transquantbypass flag from the bitstream;
determining, based on the transquantbypass flag, whether the coding unit is to be decoded using a lossless mode in which inverse transform and dequantization are bypassed during decoding of the coding unit;
when it is determined that the coding unit is to be decoded using lossless mode,
decoding, based on a scan order, a block of residuals for the coding unit using lossless mode; and
reconstructing the block of residuals by rotating the block of residuals and bypassing the dequantization.
2. The method claimed in claim 1 , wherein the transquantbypass flag is decoded from the bitstream at a coding unit level.
3. The method claimed in claim 1 , wherein rotating comprises rotating by 180 degrees.
4. The method claimed in claim 1 , wherein the scan order is one of a horizontal, vertical, zigzag, or diagonal scan order.
5. A decoding apparatus for decoding a coding unit from a bitstream, the decoding apparatus comprising a processor and memory, the processor, working together with the memory, being configured to:
decode a transquantbypass flag from the bitstream;
determine, based on the transquantbypass flag, whether the coding unit is to be decoded using a lossless mode in which inverse transform and dequantization are bypassed during decoding of the coding unit;
when it is determined that the coding unit is to be decoded using lossless mode,
decode, based on a scan order, a block of residuals for the coding unit using lossless mode; and
reconstruct the block of residuals by rotating the block of residuals and bypassing the dequantization.
6. The decoding apparatus claimed in claim 5 , wherein the transquantbypass flag is decoded from the bitstream at a coding unit level.
7. The decoding apparatus claimed in claim 5 , wherein rotating comprises rotating by 180 degrees.
8. The decoding apparatus claimed in claim 5 , wherein the scan order is one of a horizontal, vertical, zigzag, or diagonal scan order.
9. A non-transitory computer readable medium comprising instructions for decoding a coding unit from a bitstream, said instructions, when executed by a processor, cause the processor to perform at least the steps of:
decoding a transquantbypass flag from the bitstream;
determining, based on the transquantbypass flag, whether the coding unit is to be decoded using a lossless mode in which inverse transform and dequantization are bypassed during decoding of the coding unit;
when it is determined that the coding unit is to be decoded using lossless mode,
decoding, based on a scan order, a block of residuals for the coding unit using lossless mode; and
reconstructing the block of residuals by rotating the block of residuals and bypassing quantization.
10. The non-transitory computer readable medium claimed in claim 9 , wherein the transquantbypass flag is decoded from the bitstream at a coding unit level.
11. The non-transitory computer readable medium claimed in claim 9 , wherein rotating comprises rotating by 180 degrees.
12. The non-transitory computer readable medium claimed in claim 9 , wherein the scan order is one of a horizontal, vertical, zigzag, or diagonal scan order.