Encoder, decoder amd methods for enhancing a robustness for calculation of cross-component linear model parameters

A decoder for block-based decoding of picture data of a picture, the decoder being configured to decode a current block of the picture by:

• determining a first set of luma samples and a second set of luma samples in a neighborhood of the current block, the first set of luma samples comprising smaller luma values than the second set of luma samples, wherein the decoder is configured to:
• determine the first set of luma samples by finding n=2 smallest luma values in said neighborhood of the current block, and
• determine the second set of luma samples by finding n=2 largest luma values in said neighborhood of the current block;
• fitting a straight-line comprising a linear function through first pairs of luma-chroma samples and second pairs of luma-chroma samples, wherein the first pairs of luma-chroma samples are determined based on the first set of luma samples and first corresponding chroma samples in said neighborhood of the current block, and wherein the second pairs of luma-chroma samples are determined based on the second set of luma samples and second corresponding chroma samples in said neighborhood of the current block;
• and
• predicting chroma samples of the current block using luma samples of the current block and said linear function.