Geometry Transform of Intra-frames in ECM

In the design of intra prediction based on the hybrid block based coding structure, angular intra prediction is a core fundamental scheme in Advanced Video Coding (H.264/AVC), High-Efficiency Video Coding (H.265/HEVC), Versatile Video Coding (H.266/VVC), and Enhanced Compression Model (ECM). The current angular intra prediction in these codecs needs to project reference samples for northwest angular modes and can not exploit southeast angular modes. This reduces the coding efficiency obviously. To solve this problem, an algorithm of picture-level geometry transform is proposed. Three geometry transforms are supported at picture level: horizontal flip, vertical flip and clockwise 180 rotation. In addition, the chroma phase may be adjusted for cross-component prediction coding tools including Cross Component Linear Model (CCLM), Gradient Linear Model (GLM), and Convolutional Cross Component Model (CCCM). It is signaled in the picture header to indicate whether the geometry transform is applied, and which transform is used. On top of the state of the art (SOTA) ECM-6.0, simulation results demonstrate the significant efficiency improvement of the proposed geometry transform.