Efficient background video coding with static sprite generation and arbitrary-shape spatial prediction techniques
An efficient static sprite-generation and compression scheme is proposed for background video coding. First, considering both short- and long-term motion influences, a hybrid technique is proposed in the sprite generation to search the background motion relative to the generated sprite image. In order to prevent the sprite image from being blurred due to the inaccurate segmentation, a reliability-based blending technique is developed. Both the background video at every frame and the sprite image are categorized into reliable, unreliable, and undefined regions. Each region uses a unique strategy in blending. This makes the proposed technique work well even in the case of coarse segmentation. Second, an arbitrary-shape spatial prediction technique is proposed to efficiently compress the sprite image. Due to the property of the background video object, the sprite image often contains many flat and texture-correlation regions. Therefore, utilizing directional spatial prediction can significantly improve the efficiency of sprite coding. In general, the generated sprite is not a rectangular image. Since traditional spatial-prediction methods have difficulty in handling those contour blocks, a padding technique derived from rate-distortion optimization is proposed. Experimental results show that the proposed scheme can generate the background sprite image with better visual quality. Compared with the MPEG-4 sprite-coding scheme, it can also significantly improve the coding efficiency up to 3.0 dB at low bit rates.