Method and apparatus for encoding a picture

A method for encoding a picture, comprising:

• determining a first rate-distortion cost RDnon-split for a current block of said picture when said current block is not split into subblocks, from a distortion computed from each distortion for each subblock i of said current block, said distortion being scaled by an inverse of a lagrangian parameter λs(i) determined according to a quantization parameter qi assigned to said each subblock i;
• determining a first rate-distortion cost RDsplit for said current block when said current block is not split as the sum of rate-distortion costs of all subblocks in the current block using the assigned quantization parameters qi and the Lagrange parameters λs(i),
• determining that the current block is split if RDnon-split is larger than RDsplit,
• encoding the current block using a common quantization parameter q0 if the current block is not split or the subblocks in the current block using the assigned quantization parameters qi if the current block is split.

An apparatus for encoding a picture, comprising at least one processor and at least one memory, said at least one processor being configured to:

• determine a first rate-distortion cost RDnon-split for a current block of said picture when said current block is not split into subblocks, from a distortion computed for each distortion for each subblock i of said current block, said distortion being scaled by an inverse of a lagrangian parameter λs(i) determined according to a quantization parameter qi assigned to said each subblock
• determine a first rate-distortion cost RDsplit for said current block when said current block is not split as the sum of rate-distortion costs of all subblocks in the current block using assigned quantization parameters qi and the Lagrange parameters λs(i);
• determine that the current block is split if RDnon-split is larger than RDsplit;
• encode the current block using a common quantization parameter q0 if the current block is not split or the subblocks in the current block using the assigned quantization parameters qi if the current block is split.