為了把物體表面呈現的更真實，六維函數BTFs ( Bidirectional Texture Functions)目前已經被使用的相當頻繁，但BTFs的資料量實在太大而沒辦法直接使用，為了解決資料龐大的問題，傳統的SBRDF以逼近光反射模型參數，來達到資料壓縮的效果，但是SBRDF對於表面的凹凸所產生的陰影及遮蔽，不能達到逼真的呈現，為了改善這個問題，我們選擇從物理方面，找出資料中陰影和遮蔽等屬於表面幾何的資料並去除，使參數更正確，同時利用兩個物理現象去區分陰影及遮蔽為兩個互不干涉資料，第一是陰影不會因視角不同而改變，第二是遮蔽不因光線方向不同而改變，經過這些分析，我可以利用SBRDF加上附加的陰影及遮蔽兩種獨立的效應，來達到彷彿跟未壓縮過的BTFs一樣的真實繪圖。

In order to draw a photorealistic surface, Bidirectional Texture Functions(BTFs), a 6D texture function which extends Bidirectional Reflectance Distribution Function(BRDF) to include the self-shadowing, self-occlusion and inter-reflection effects, has been mentioned frequently in recent years. Its main drawback is its massive data size. To solve this, Spatial Bidirectional Reflectance Function (SBRDF) techniques compress BTFs into reflectance model parameters. However, SBRDF cannot produce
the self-shadowing and self-occlusion effects in real-world surface geometry. This work is aimed to this drawback. I find how self-shadowing and self-occlusion affect the surface by additional physical-based analysis. And I rely on two physical phenomena to divide self-shadowing and self-occlusion into two independent effects. First, self-shadowing is view independent. Second, self-occlusion is independent of lighting direction changes. After these analyses, I use SBRDF and additional self-shadowing and self-occlusion I found to render a photorealistic surface as non-compressed BTFs doing.

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