Enhanced Intra Block Copy with Planar Perspective Transformation for Urban Building Scenes.

In this paper, we propose an enhanced intra block copy method for intra prediction in HEVC through planar perspective transformation for urban building scenes. Since the imaging plane of the camera is not always fronto-parallel to the facades of buildings (object plane) in the image, repetitive patterns on object plane in 3D space appear with scale shift in the image, and the corresponding redundancy cannot be removed through conventional intra block copy based on translational motion model. To solve this problem, we start with theoretic analysis to perspective transformation, and get that the two-parametered planar perspective transformation is the cause of scale shift. Therefore, intra block copy can be enhanced via rectification through planar perspective transformation, whose detailed parameters are derived through vanishing points detected in the image. To achieve the best performance, rate-distortion optimization is utilized to determine whether planar perspective transformation would be used in intra block copy for coding unit (CU) or not. In this way, we enable much more flexible prediction for both non-local translational and non-local perspective repeated image content. Experimental results show that our proposed method can achieve as the highest as 9.9% and averagely 2.9% bit-rate saving on the test images for urban building scenes compared to conventional intra block copy on HEVC platform.