三維動態模型之動作轉移與形變

Abstract

近年來，隨著電影、電腦遊戲的發達，許多場景不再是單純由動畫師一張張手繪 而成，取而代之的是電腦動畫的廣泛被應用。而三維模型以及三維模型動畫的產 生便是電影、遊戲工業裡很重要的一環。為了要讓三維模型能產生動作，大部分 的方法是先替這三維模型產生一個骨幹，以及設立模型網格與骨幹關係的權重， 然後在按照動畫師的意思慢慢地調整三維模型關鍵影格的姿勢，以產生一段平順 的三維動畫。這並不是一件簡單易做的事，尤其當要處理一個像是戰爭場面那種 複雜的場景，許多的三維士兵的模型需要被賦予動作，動畫師將要一個一個模型 地替他編輯姿勢，既使都只是要產生相同的走路動作。於是若有一個系統能幫我 們把已經產生的動畫套到其他三維模型上，那麼將是一個對動畫師而言很有幫助 的系統。 我們在此論文中實行了一個動作轉移的系統，能將來源的三維模型的動作複製到 目標三維模型上，也能替目標三維模型產生與來源模型一樣的骨幹與類似的權重 關析，而這些資訊是目標三維模型原本沒有的。除此之外，我們還能替來源與目 標模型在動作的同時產生三維外貌形變，這可以幫助動畫師利用原本既有的動作 與模型來快速產生一個新的模型。 我們的演算法主要是根據過去已提出過的方法加以改進。把來源與目標模型切成 很多共同的區塊後，利用一些參數化的方法我們可以得到來源與目標模型兩表面 的對應關係。接著利用一些紀錄骨幹位置的方法，我們便可以將來源的骨幹、權 重關係以及動畫關鍵影格轉移到目標模型上，以期讓目標模型擁有與來源模型類 似的動作。同時參數化也可以用來做三維外貌的形變。 我們提出了一個改進的方法，讓動作轉移的結果更好也更節省使用者介入的人工 操作時間。這系統的操作流程簡單易懂，使用者只需點選來源與目標模型外表上 的對應特徵點即可提動作轉移與外貌形變的功能。

Animation has been manipulated widely in movies and video games nowadays. To make a 3D model move, traditionally, requires animators’ efforts to edit the key poses of the model. It is a time-consuming task, especially when dealing with an imposing scene such as those full of different animals or soldiers. In this thesis, we proposed an improved method in transferring skeleton-driven motions from one model to another. To transfer the motions of the source model to the target one, we need to construct animation data for the target model which has only mesh information. Such animation data we deal with are the skeleton, binding-weight, and key-frames poses information. The basic idea of our system is utilizing the surface parameterization to get a bijective mapping between the surfaces of two models. And by recording the animation data from the source model as the attributes of the vertices, we can transfer the motions from the source model to the target one. Using the surface mapping information, we also can also do morphing effect which can transform the source shape into the target shape. Combining the mesh morphing techniques and the motion transition techniques, animated morphing sequences are generated which morph the shape and the motion simultaneously and smoothly between two models. The skeleton and binding weight can be transferred in our system instead of spending lots of time in creating them by some author tools. The animation sequence can be reused and it is useful when dealing with the scenes which are filled with background crowds with almost similar motions. Moreover animated morphing technique is not only a special effect but also can help us to create some new models which are blended by several existing animated models.