利用單張影像3D回復技術之數位物件萃取合成系統應用於變異性光線及光影環境中之研究

王亮川
Matting and Compositing is originally used to deal with special effects composition problem in the movie technology, that is, in the boundary regions of object and background intersection, if it is a more complicated texture, such as tree, hair, water, smoke and some properties of light transmittance etc., the refraction of light will make pixel to receive the lights that come from object and background simultaneously, and this proportion of mix is called “Alpha Value”.

Thus, in order to lower the complexity of background, it costs much money to build “Blue Screen” in a film studio, and then take object in there, but, it might generate the background-colored image in the boundary regions, and the color of object must differ from blue screen, it also can’t be used to natural image. Besides, it is very easy to obtain digital image, how to save hardware costs and to apply to nature life, obtaining a more real and beautiful compositing image, it is still our objective. In this paper, we propose a new 3D based digital matting and compositing system, that use digital matting to deal with the object which boundary has property of light transmittance, and use automatic white balancing to deal with light source condition consistency between the object and new background. In addition, use Shape from Shading (SFS) to reconstruct 3D depth information of object, and relight according to light source direction of new background to deal with shading condition consistency between the object and new background, these will make compositing image more harmonious between the object and new background, also make compositing image more real and natural, and it is not easy to be seen through by eyes.

萃取與合成技術(Matting and Compositing)，最早原本只是用以解決電影科技中的特效合成問題，即處理在前景物件與新背景交接的邊緣區域(Boundary Regions)，若是較為複雜的材質特性，如：樹木、毛髮、水、煙或一些具透光性(Light Transmittance)的材質等，因為光線的折射(Refraction)，造成影像中之像素同時接收到前景與背景的光線，此混合(Mix)的比例稱為Alpha值(Alpha Value)。所以，為了降低原背景的複雜度(Complexity)，往往需要花費昂貴的成本於攝影棚內搭建藍幕(Blue Screen)的背景，並將前景物件置於其中，但在前景物件的邊緣區域也可能會產生泛著原背景顏色的現象，且前景物件不能與藍幕背景顏色相同，也無法應用於一般現實生活的場景之中。此外，數位化影像的取得十分容易，如何在既能節省昂貴的硬體成本，又能兼具生活實用性下，獲得較為真實與完美的影像合成品質，也是我們一直想要達到的目標。因此，本論文提出了一個全新以3D技術為基礎的數位物件萃取與合成系統，使用了物件萃取技術(Digital Matting)來解決邊緣具有透光特性的前景物件，也使用了自動白平衡技術(Automatic White Balancing)來解決前景物件與新背景之間的光線狀態一致性問題。並且，還利用單張影像3D回復技術(Shape from Shading, SFS)來重建前景物件之3D深度資訊，並依新背景的光源方向進行重新打光(Relighting)，來解決前景物件與新背景之間的光影狀態一致性問題，這將使得影像合成後的前景物件與新背景更能相互地融合，也使得結果更加地真實與完美，且較不易被肉眼所識破。