Adaptive Chroma Block Vector Derivation from Luma for Screen Content Coding

Intra Block Copy (IBC) and Intra Template Matching Prediction (IntraTMP) are two efficient algorithms to sufficiently exploit the correlation in the same picture. Block Vector (BV) is used to represent the displacement between the current block and its reference within the same picture. The BV information of luma can be employed to help the chroma coding efficiently. Based on this feature, an adaptive chroma prediction is proposed to derive the BV of the chroma block from the luma. Two strategies are designed to improve the coding performance, including multiple positions’ check and template-based BV refinement. Compared with Enhanced Compression Model (ECM) of beyond VVC, 0.43%, 0.35%, and 0.60% BD-rate savings for Y, Cb, and Cr components are achieved for Class F, and 2.23%, 2.31%, and 2.93% BD-rate savings are provided for Class TGM. We also integrated the proposed method into the VVC Test Model (VTM). A similar coding improvement can be observed. Due to the coding gain and low complexity, the proposed method has been adopted into the beyond VVC exploration and integrated into the latest version of ECM.