Complexity Reduction of Template Matching-Based Reference Picture Padding in Video Coding

Abstract

Reference Picture Padding removes the restriction for motion vectors to point completely inside the reference picture. Removing this restriction increases the compression efficiency and is, therefore, applied in many video coding standards. However, artifacts can occur at the picture boundaries if the surroundings of the reference picture are not predicted accurately by the employed method. This especially becomes a problem in viewport-adaptive streaming scenarios if the independently decodable subpictures of Versatile Video Coding (VVC) are used. In this case, the subpicture boundaries behave equivalently to picture boundaries. The boundary-related artifacts then may become visible in the viewport. It has been shown that artifacts can be reduced by using a template matching-based padding algorithm. The main drawback of this algorithm is its high computational complexity. We propose a complexity reduction of the search step by reusing the results of previous searches and an advanced chroma handling. The proposed algorithm reduces the decoder runtime increase from 31.3% to 19.2% alongside slightly increased compression efficiency in a subpicture-coding scenario. An alternative variant of the algorithm reduces the decoder runtime increase to 12.9% while only sacrificing about 15% of the compression gains compared to the first variant.