Methods and devices for coding and decoding a data stream representative of at least one image

A coding method for coding a coded data stream representative of at least one image by a coding device, said image being split into blocks, the coding method comprises, for at least one block of the image, referred to as a current block:

• coding an item of information indicating a coding mode of the current block,
• determining a coding mode of the current block from among at least a first and a second coding mode;
• when the coding mode of the current block corresponds to a first coding mode, coding the current block comprising determining a first quantization step according to a quantization parameter to quantize a prediction residue associated with the current block in a transform domain,
• when the coding mode of the current block corresponds to a second coding mode, coding the current block comprising determining the first quantization step and determining a second quantization step to quantize a prediction residue associated with the current block in a spatial domain,
• the second quantization step being determined according to the first quantization step.

A device for decoding a coded data stream representative of at least one image, said image being split into blocks, wherein the decoding device comprises:

• a processor (PROC0) configured, for at least one block of the image, referred to as a current block, to:
• decode an item of information indicating a coding mode of the current block,
• determining a coding mode of the current block from among at least a first and a second coding mode;
• when the coding mode of the current block corresponds to the first coding mode, decode the current block by determining a first quantization step according to a quantization parameter to dequantize, in a transform domain, a prediction residue associated with the current block,
• when the coding mode of the current block corresponds to the second coding mode, decode the current block by determining the first quantization step according to the quantization parameter and determining a second quantization step to dequantize, in a spatial domain, a prediction residue associated with the current block,
• the second quantization step being determined according to the first quantization step.

A coding device for coding a coded data stream representative of at least one image, said image being split into blocks, wherein the coding device comprises:

• a processor configured, for at least one block of the image, referred to as a current block, to:
• code an item of information indicating a coding mode of the current block,
• determining a coding mode of the current block from among at least a first and a second coding mode;
• when the coding mode of the current block corresponds to the first coding mode, code the current block by determining a first quantization step according to a quantization step to quantize a prediction residue associated with the current block in a transform domain,
• when the coding mode of the current block corresponds to the second coding mode, code the current block by determining the first quantization step according to the quantization parameter and determining a second quantization step to quantize a prediction residue associated with the current block in a spatial domain,
• the second quantization step being determined according to the first quantization step.

A non-transitory computer-readable medium comprising instructions stored thereon which when executed by a processor of a decoding device configure the decoding device to:

• decode a coded data stream representative of at least one image performed by a decoding device, said image being split into blocks, the decoding comprising, for at least one block of the image, referred to as a current block:
• decoding an item of information indicating a coding mode of the current block,
• determining a coding mode of the current block from among at least a first and a second coding mode,
• when the coding mode of the current block corresponds to the first coding mode, decoding the current block comprising determining a first quantization step according to a quantization parameter to dequantize, in a transform domain, a prediction residue associated with the current block,
• when the coding mode of the current block corresponds to the second coding mode, decoding the current block comprising determining the first quantization step according to the quantization parameter and determining a second quantization step to dequantize, in a spatial domain, a prediction residue associated with the current block,
• the second quantization step being determined according to the first quantization step.