這篇論文提出一個新方法來估計分析頭部有較大的轉動下的臉部表情，在作臉部表情分析時，首先要將Non-Rigid 的臉部表情與Rigid 的頭部轉動分離。為了克服一般常見的“Affine Model”與“8-parameter Perspective Projection model”的缺點，如：Out-of-plane motion、人臉的凹凸深度變化（明顯如鼻頭與眼角），在論文中所提的方法利用了3D 人頭Model 來幫助模擬。另外，利用Optical Flow 來追蹤所選取的特徵點，這些特徵點有只受轉動（Rigid Motion）影響的點與估計表情變化的點，將Tracking 的結果Mapping 到3D 人頭Model，估計出轉動後，利用3D 人頭Model 模擬正面時的表情，以完成Rigid Motion 與Non-Rigid Motion的分離。

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