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

摘要

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. The method comprises: deriving 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 comprising reconstructed luma samples neighbouring the current luma block that are downsampled to match chroma resolution; and obtaining the chroma sample using the linear model with the one or more parameters derived and the associated downsampled reconstructed luma sample in the current luma block. Downsampling reconstructed luma samples to match chroma resolution involves obtaining one from a plurality of reference downsampling schemes, the schemes including at least one subsampling 1-tap filters 901-906 that each selects, as downsampled reconstructed luma sample one different reconstructed luma sample (e.g. luma pixel above 901, above-right 903, below 902, or below-right 904 the chroma location) adjacent the downsampling position. Other independent claims generalise chroma/luma to first/second colour components and claim CCLM modes where sample sets to derive linear model parameters are selected from sample sets including at least one irregular (non-rectangular) sample set.