New sample sets and new down-sampling schemes for linear component sample prediction

A method of obtaining a first-colour-component sample for a current first-colour-component block of a multi-colour-component frame from an associated reconstructed second-colour-component sample of a current second-colour-component block in the same frame using a linear model with one or more parameters, the two blocks having the same size, the method comprising:

• deriving the one or more parameters of the linear model based on a neighbouring first-colour-component sample set comprising first-colour-component samples neighbouring the current first-colour-component block and a neighbouring second-colour-component sample set comprising reconstructed second-colour-component samples neighbouring the current second-colour-component block, and
• obtaining the first-colour-component sample using the linear model with the one or more parameters derived and the associated reconstructed second-colour-component sample in the current second-colour-component block,
• wherein deriving the one or more parameters includes obtaining one from a plurality of reference sample sets to define the neighbouring first-colour-component and second-colour-component sample sets for the parameter derivation, the plurality of reference sample sets including one or more irregular sample sets,
• wherein an irregular sample set is built from two lines of outer neighbouring samples parallel and adjacent to the top boundary of the current block and the two lines of outer neighbouring samples parallel and adjacent to the left boundary of the current block, and for at least one position along the top or left boundary of the current block, only one sample is selected from the sample of the first line adjacent to the boundary and the sample of the next and second line, and at least one sample of the next and second line along the same boundary is selected.

A method of obtaining a chroma sample for a current chroma block from an associated reconstructed luma sample of a current luma block in the same frame using a linear model with one or more parameters, the method comprising:

• deriving the one or more parameters of the linear model based on a neighbouring chroma sample set comprising chroma samples neighbouring the current chroma block and a neighbouring luma sample set, the neighbouring luma sample set comprises reconstructed luma samples neighbouring the current luma block that are down-sampled to match chroma resolution,
• obtaining the chroma sample using the linear model with the one or more parameters derived and the associated reconstructed luma samples in the current luma block made of reconstructed luma samples down-sampled to match chroma resolution,
• obtaining one reference LM mode from a plurality of reference LM modes, each of which being made of one down-sampling scheme and one sample set, to down-sample, using the thus-obtained down-sampling scheme, the reconstructed luma samples to match chroma resolution for the parameter derivation and for the chroma intra predictor generation and to define, using the thus-obtained sample set, the neighbouring luma and chroma sample sets for the parameter derivation,
• wherein at least one reference LM mode includes an irregular sample set built from two lines of outer neighbouring samples parallel and adjacent to the top boundary of the current block and the two lines of outer neighbouring samples parallel and adjacent to the left boundary of the current block, and for at least one position along the top or left boundary of the current block, only one sample is selected from the sample of the first line adjacent to the boundary and the sample of the next and second line, and at least one sample of the next and second line along the same boundary is selected.

A device for obtaining a first-colour-component sample for a current first-colour-component block of a multi-colour-component frame from an associated reconstructed second-colour-component sample of a current second-colour-component block in the same frame using a linear model with one or more parameters, the two blocks having the same size, the device comprising at least one microprocessor configured for carrying out the steps of:

• deriving the one or more parameters of the linear model based on a neighbouring first-colour-component sample set comprising first-colour-component samples neighbouring the current first-colour-component block and a neighbouring second-colour-component sample set comprising reconstructed second-colour-component samples neighbouring the current second-colour-component block, and
• obtaining the first-colour-component sample using the linear model with the one or more parameters derived and the associated reconstructed second-colour-component sample in the current second-colour-component block,
• wherein deriving the one or more parameters includes obtaining one from a plurality of reference sample sets to define the neighbouring first-colour-component and second-colour-component sample sets for the parameter derivation, the plurality of reference sample sets including one or more irregular sample sets,
• wherein an irregular sample set is built from two lines of outer neighbouring samples parallel and adjacent to the top boundary of the current block and the two lines of outer neighbouring samples parallel and adjacent to the left boundary of the current block, and for at least one position along the top or left boundary of the current block, only one sample is selected from the sample of the first line adjacent to the boundary and the sample of the next and second line, and at least one sample of the next and second line along the same boundary is selected.

A device for obtaining a chroma sample for a current chroma block from an associated reconstructed luma sample of a current luma block in the same frame using a linear model with one or more parameters, the device comprising at least one microprocessor configured for carrying out the steps of:

• deriving the one or more parameters of the linear model based on a neighbouring chroma sample set comprising chroma samples neighbouring the current chroma block and a neighbouring luma sample set, the neighbouring luma sample set comprises reconstructed luma samples neighbouring the current luma block that are down-sampled to match chroma resolution,
• obtaining the chroma sample using the linear model with the one or more parameters derived and the associated reconstructed luma samples in the current luma block made of reconstructed luma samples down-sampled to match chroma resolution,
• obtaining one reference LM mode from a plurality of reference LM modes, each of which being made of one down-sampling scheme and one sample set, to down-sample, using the thus-obtained down-sampling scheme, the reconstructed luma samples to match chroma resolution for the parameter derivation and for the chroma intra predictor generation and to define, using the thus-obtained sample set, the neighbouring luma and chroma sample sets for the parameter derivation
• wherein at least one reference LM mode includes an irregular sample set built from two lines of outer neighbouring samples parallel and adjacent to the top boundary of the current block and the two lines of outer neighbouring samples parallel and adjacent to the left boundary of the current block, and for at least one position along the top or left boundary of the current block, only one sample is selected from the sample of the first line adjacent to the boundary and the sample of the next and second line, and at least one sample of the next and second line along the same boundary is selected.