Joint Cross-Component Linear Model For Chroma Intra Prediction

The Cross-Component Linear Model (CCLM) is an intra prediction technique that is adopted into the upcoming Versatile Video Coding (VVC) standard. CCLM attempts to reduce the inter-channel correlation by using a linear model. For that, the parameters of the model are calculated based on the reconstructed samples in luma channel as well as neighboring samples of the chroma coding block. In this paper, we propose a new method, called as Joint Cross-Component Linear Model (J-CCLM), in order to improve the prediction efficiency of the tool. The proposed J-CCLM technique predicts the samples of the coding block with a multi-hypothesis approach which consists of combining two intra prediction modes. To that end, the final prediction of the block is achieved by combining the conventional CCLM mode with an angular mode that is derived from the co-located luma block. The conducted experiments in VTM-8.0 test model of VVC illustrated that the proposed method provides on average more than 1.0% BD-Rate gain in chroma channels. Furthermore, the weighted YCbCr bitrate savings of 0.24% and 0.54% are achieved in 4:2:0 and 4:4:4 color formats, respectively.