Hybrid model sprite generation: A high-quality, fast and robust algorithm

Sprite generation, the core of the sprite coding, is a developing technique included in the MPEG-4 standard. It achieves high subjective quality with low bitrates. The affine and perspective GME (Global Motion Estimation) methods are demonstrated in the MPEG-4 Verification Model (MPEG-4 VM), MPEG-4 Optimization Model (MPEG-4 OM) and many other algorithms. The affine model GME, provides limited image quality, is robust and fast. The perspective model GME generates sprites with better quality, however it suffers from the time-wasting and error propagation problem. A new method to generate sprites in this paper combines the existing affine and perspective GME algorithms to produce high sprites quickly without losing robustness. In order to generate high quality sprites, the proposed "Hybrid Model GME" method uses the affine model GME as an initial search, then switches to the perspective model GME if necessary. To accelerate the speed, a nearest neighborhood (NN) kernel is used to replace the bilinear method for image warping. Experimental results show that the image quality is much improved even when camera movements are more complex and quick. The computation speed is between 10 and 17 times faster than the MPEG-4 VM. If the sprites can be divided into several pieces, the computation speed can be about 1.46 times faster ahead.