| CPC H04N 19/11 (2014.11) [H04N 19/105 (2014.11); H04N 19/117 (2014.11); H04N 19/176 (2014.11); H04N 19/593 (2014.11)] | 11 Claims |
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1. An image decoding method performed by an image decoding apparatus, the image decoding method comprising:
deriving an intra prediction mode of a current chroma block;
selecting one or more luma reference sample lines for a current luma block corresponding to a current chroma block based on the intra prediction mode of the current chroma block being inter-component intra prediction mode;
deriving downsampled luma reference samples based on the luma reference sample lines;
deriving chroma reference samples for the current chroma block;
deriving prediction parameters for inter-component intra prediction using the downsampled luma reference samples and the chroma reference samples; and
generating a prediction block by performing the inter-component intra prediction for the current chroma block based on the current luma block and the prediction parameters,
wherein based on an upper boundary of the current luma block corresponding to an upper boundary of a coding tree block, one upper reference sample line adjacent to the current luma block is selected and three left reference sample lines neighboring of the current luma block are selected,
wherein an upper downsampled luma reference sample for prediction parameters is derived based on three reference samples selected from the one upper reference sample line,
wherein a left downsampled luma reference sample for the prediction parameters is derived based on six reference samples selected from the three left reference sample lines,
wherein the chroma reference samples include an upper chroma reference sample and a left chroma reference sample, and
wherein the prediction parameters are derived by using the upper downsampled luma reference sample derived based on the three reference samples, the left downsampled luma reference sample derived based on the six reference samples, the upper chroma reference sample and the left chroma reference sample.
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