莊永裕臺灣大學：資訊工程學研究所林宗勳Lin, Tsung-HsunTsung-HsunLin2007-11-262018-07-052007-11-262018-07-052007http://ntur.lib.ntu.edu.tw//handle/246246/54073在日常生活中，半透明是一個吸引人並且重要的效果。但對電腦繪圖而言，如何有效率的繪製半透明材質卻是一個不容易的挑戰。在本篇論文中，我們提出一個新的方式繪製半透明的效果，它是基於幾何圖像(geometry image)以影像濾波處理的方式繪製半透明材質。我們亦提出一個階層式的影像濾波器設計，利用它來進行繪製半透明材質所需要的對面積積分的動作。我們採用二階段照明的方式。在第一階段先計算光線照到物體表面時所接收到光的能量，第二階段再利用影像濾波器將第一階段的結果積分成為半透明的效果。最後，我們將這個演算法實作在可程式化的繪圖處理器上(programmable GPU)，達到即時半透明材質繪圖。Translucency is an attractive and important effect, but it is also a challenge to synthesize efficiently in computer graphics. In this thesis, we propose a new image filter method to render translucent objects based on geometry images. we design the image filter as a hierarchical structure, and we precompute the BSSRDF diffuse scattering term before rendering. We adopt a two-pass illumination approach, which decouples the computation of irradiance at the surface from the evaluation of scattering inside the material. we apply the algorithm on current programmable GPU and reach real-time performance for translucent object rendering.1 Introduction to Translucent Rendering 1 2 Previous Work 2 2.1 A Practical Model for Subsurface Light Transport . . . . . . . . . . . . . . . 2 2.2 A Rapid Hierarchical Rendering Technique for Translucent Materials . . . . 2 2.3 Interactive Rendering of Translucent Objects . . . . . . . . . . . . . . . . . . 3 2.4 Interactive Subsurface Scattering for Translucent Meshes . . . . . . . . . . . 4 2.5 Translucent Shadow Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.6 GPU Algorithms for Radiosity and Subsurface Scattering . . . . . . . . . . . 6 2.7 Interactive Rendering of Translucent Deformable Objects . . . . . . . . . . . 7 2.8 Efficient Rendering of Local Subsurface Scattering . . . . . . . . . . . . . . . 8 2.9 All-Frequency Interactive Relighting of Translucent Objects with Single and Multiple Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 Bidirectional Surface Scattering Re°ectance Distribution Function (BSS- RDF) 10 3.1 Multiple Scattering Approximation . . . . . . . . . . . . . . . . . . . . . . . 10 3.2 The Importance of Multiple Scattering . . . . . . . . . . . . . . . . . . . . . 11 4 Translucent Effect Rendering 13 4.1 Geometry Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.2 Two-Pass Illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.3 BSSRDF Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5 Improve Rendering Efficiency 17 5.1 Locality of Subsurface Scattering Effect . . . . . . . . . . . . . . . . . . . . 17 5.2 Precomputing The Dipole Approximation Rd(r) . . . . . . . . . . . . . . . . 17 5.3 BSSRDF Image Filter Design . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6 Implementation 18 6.1 Precomputing The Dipole Approximation Rd(r) . . . . . . . . . . . . . . . . 19 6.2 Avoid Flaws on Texture Boundary . . . . . . . . . . . . . . . . . . . . . . . 20 7 Results 21 7.1 The Bottlenecks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8 Conclusions And Future Work 231350503 bytesapplication/pdfen-US半透明度材質真實影像合成表層內散射幾何圖像反射模型Translucency renderingSubsurface scatteringGeometry imagesBSSRDFReflection modelsthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/54073/1/ntu-96-P93922002-1.pdf