A luma-based chroma intra-prediction method includes: applying, by a filter circuit with a first weighting table, weighting to reconstructed luma samples to generate a first down-sampled luma sample, wherein the reconstructed luma samples are external to a luma block; computing parameters of a linear model, wherein a pair of the first down-sampled luma sample and a reconstructed chroma sample that is external to a chroma block is involved in computing the parameters of the linear model; and determining a predicted value of a chroma sample included in the chroma block according to the linear model and a second down-sampled luma sample that is derived from the luma block.