Method and apparatus for encoding a picture
A method and an apparatus for encoding a picture are disclosed. Such method comprises: —determining a rate-distortion cost ( 41 ) for a current block of said picture when said current block is not split into subblocks, taking into account quantization parameters assigned to the subblocks of said current block, —determining ( 42 ) whether said current block is split or not according at least to the determined rate-distortion cost, —encoding ( 43 ) the current block according to the result of determining whether a current block is split or not into subblocks.
1. A method for encoding a picture comprising:
computing a first rate-distortion cost for a current block in a splitting configuration of the picture as a sum of rate-distortion costs computed for each subblock of the current block according to the splitting configuration, the rate-distortion cost computed for a subblock depending on a distortion computed for the subblock reconstructed from coding parameters providing a lowest rate-distortion cost and a quantization parameter previously assigned to the subblock;
computing a second rate-distortion cost for the current block in a non-splitting configuration of the picture, the rate-distortion cost computed for the current block depending on a distortion computed for the current block reconstructed from coding parameters providing the lowest rate-distortion cost and quantization parameters previously assigned to the subblocks of the current block and using as a Lagrange parameter a maximum value of Lagrange parameters associated with the quantization parameter assigned to subblocks of the current block;
determining whether to split the current block into subblocks for encoding according to the first rate-distortion cost and the second rate-distortion cost, resulting in an encoding split determination; and
encoding the current block according to the encoding split determination.
2. The method according to claim 1 , wherein computing the second rate-distortion cost comprises assigning an infinite value as the second rate-distortion cost when the current block includes at least two subblocks to which different quantization parameters have been previously assigned.
3. The method according to claim 1 , further comprising using as the Lacirancie parameter a maximum value of Lagrange parameters associated with the quantization parameters assigned to subblocks of the current block for computing the first rate-distortion cost.
4. The method according to claim 3 , further comprising using as a quantization parameter a minimum value of the quantization parameters assigned to subblocks of the current block for computing the second rate-distortion cost.
5. The method according to claim 1 , further comprising:
assigning to the current block a quantization parameter equal to the minimum value of the quantization parameters assigned to subblocks of the current block;
computing, for the current block, a new Lagrange parameter according to the quantization parameter assigned to the current block;
determining a rate-distortion cost for a large block using at least the new Lagrange parameter, wherein the large block is larger than the current block and comprises the current block as a subblock;
determining whether to split the large block for encoding.
6. An apparatus for encoding a picture comprising:
a processor and a memory storing instructions that, when executed by the processor, cause the apparatus to:
compute a first rate-distortion cost for a current block in a splitting configuration of the picture, as a sum of rate-distortion costs computed for each subblock of the current block according to the splitting configuration, the rate-distortion cost computed for a subblock depending on a distortion computed for the subblock reconstructed from coding parameters providing a lowest rate-distortion cost and a quantization parameter previously assigned to the subblock;
compute a second rate-distortion cost for the current block in a non-splitting configuration, depending on a distortion computed for the current block in the non-splitting configuration and taking into account quantization parameters previously assigned to the subblocks of the current block and using as a Lagrange parameter a maximum value of Lagrange parameters associated with the quantization parameter assigned to subblocks of the current block;
determine whether to split the current block into subblocks for encoding according to the first rate-distortion cost and the second rate-distortion cost, resulting in an encoding split determination; and
encode the current block according to the encoding split determination.
7. The apparatus according to claim 6 , wherein computing the second rate-distortion cost comprises assigning an infinite value as the second rate-distortion cost when the current block includes at least two subblocks to which different quantization parameters have been previously assigned.
8. The apparatus according to claim 6 , wherein the apparatus is further configured to use as the Lagrange parameter a maximum value of Lacirancie parameters associated with the quantization parameters assigned to subblocks of the current block for computing the first rate-distortion cost.
9. The apparatus according to claim 8 , wherein the apparatus is further configured to use as a quantization parameter a minimum value of the quantization parameters assigned to subblocks of the current block for computing the second rate-distortion cost.
10. The apparatus according to claim 6 , wherein the processor is further configured to:
assign to the current block a quantization parameter equals to the minimum value of the quantization parameters assigned to subblocks of the current block;
compute, for the current block, a new Lagrange parameter according to the quantization parameter assigned to the current block;
determine a rate-distortion cost for a large block, using at least the new Lagrange parameter, wherein the large block is larger than the current block and comprises the current block as a subblock;
determine whether to split the large block for encoding.
11. A non-transitory computer-readable medium including instructions for causing one or more processors to perform:
computing a first rate-distortion cost for a current block in a splitting configuration of the picture as a sum of rate-distortion costs computed for each subblock of the current block according to the splitting configuration, the rate-distortion cost computed for a subblock depending on a distortion computed for the subblock reconstructed from coding parameters providing a lowest rate-distortion cost and a quantization parameter previously assigned to the subblock;
computing a second rate-distortion cost for the current block in a non-splitting configuration of the picture, the rate-distortion cost computed for the current block depending on a distortion computed for the current block reconstructed from coding parameters providing the lowest rate-distortion cost and quantization parameters previously assigned to the subblocks of the current block and using as a Lagrange parameter a maximum value of Lagrange parameters associated with the quantization parameter assigned to subblocks of the current block;
determining whether to split the current block into subblocks for encoding according to the first rate-distortion cost and the second rate-distortion cost, resulting in an encoding split determination; and
encoding the current block according to the encoding split determination.