Global Motion Estimation in Sprite Generation by Eliminating Local Object Motions

In this paper, a new feature point selection method for the global motion estimation(GME) in sprite generation is proposed. GME for the sprite generation presented in this paper consists of two stages, feature selection and global motion estimation with selected blocks. First, local object motions are distinguished from the static background. Blocks with local motions are excluded in the subsequent procedure because local object motions would not be helpful to GME and often are even harmful to the exact motion estimation. Note that sprite generation mainly concerns the generation of the static background for a sequence of image frames. To identify local motions, conventional block-based motion estimation is performed for the blocks in the current frame. If it has a greater residual error than a threshold, this block is considered to have an object with local motions and is excluded in the subsequent procedure. Note that a large residual error of a block implies a change in the shape of the object and the block image could not be a part of the static background. The second stage extracts edges in the image excluding blocks selected in the first step and they are used for GME. Experiments show the proposed algorithm performs faster in selected images than existing methods with improved objective/subjective quality.