Improved Chroma From Luma Intra Prediction Mode Beyond AV1.

In AV1, Chroma from Luma (CfL) intra prediction mode is adopted to predict chroma samples by exploiting the linear correlation between the co-located samples of luma and chroma components, wherein the scaling factor of the linear model is transmitted to the decoder side and the offset factor is derived as the average of neighboring chroma pixels. In this paper, the CfL prediction mode is improved in following three aspects. Firstly, the calculation of DC contribution between luma and chroma is aligned to improve the accuracy of CfL prediction. Secondly, to further enhance the CfL prediction mode, a new cross-component intra prediction mode without signaling of scaling factor is employed. Thirdly, the down-sampling filter for CfL mode is adaptively selected at the encoder side for each video sequence. Simulation results show that, on top of AOMedia Video Model (AVM) v3.0.0, an average coding gain of 0.9%, 0.5%, and 0.4% in terms of YUV-PNSR is achieved for all intra, random access, and low delay configurations, respectively.