使用可適性多層次渲染與去雜訊之高效雲端虛擬光場渲染系統

Abstract

隨著虛擬實境（VR）與擴增實境（AR）的蓬勃發展，發展出即時且 具有全域照明效果的渲染技術逐漸成為許多研究的主軸。然而，現今 的客戶端裝置如智慧型手機等仍然無法負擔全域照明演算法的龐大計 算量。例如光線追蹤（Ray-Tracing）演算法需要在場景中計算數百萬條 的光束，因而無法在客戶端裝置上即時運算。為了解決這個問題，部 分學者提出使用光場渲染（Light Field Rendering）技術來支援客戶端裝 置的顯示。這些光場影像可以透過預先計算後，傳送至客戶端裝置並 進行即時色彩取樣來顯示畫面。除了可以讓使用者擁有自由視角顯示 之外，還提供許多相機效果如景深與變焦。為了要快速且有效率的產 生這些光場圖，我們提出了結合DIBR (Depth-Image-Based-Rendering) 與光線追蹤的光場渲染演算法。透過動態錯誤偵測與回饋機制，我們 可以在傳統光線追蹤與DIBR 間取得最佳平衡。此外，為了更進一步 利用光場影像間像素共用的特性來加速計算，我們提出了多層次渲染 的概念。為了證明我們的概念可行，我們基於這個架構實作了一套包 含伺服器與客戶端的雲端光場渲染系統雛形。經實驗證實，藉由我們 的新方法，渲染系統可以在簡單的場景如Cornell Box 中加速達224%。 就算是複雜場景如Conference Room 或Sponza Palace，速度提升也可 達到100% 以上。

Real-time global illumination rendering is very desirable for emerging applications such as Virtual Reality (VR) and Augmented Reality (AR). However, client devices have difficulties to support photo-realistic rendering, such as Ray-Tracing, due to insufficient computing resources. Many modern frameworks adopted Light Field rendering to support device displaying. A Light Field can be precomputed and store in cloud. During runtime, the display extracts the colors from the Light Field to generate arbitrary real time viewpoints or re-focusing within a predefined area. To efficiently compute the Light Field, We have combined DIBR (Depth-Image-Based-Rendering) and traditional ray-tracing in an adaptive fashion to synthesize images. By measuring the color errors during runtime, we adaptively determine the right balance between DIBR and Ray Tracing. To further optimize the computation efficiency, we also added a multi-level design to exploit the degree of shareable pixels among images to control the computation for error removal. In order to demonstrate our idea, we implemented a cloud-based Light Field rendering system with viewer application. Using our approach, we can reach similar quality with much fewer ray samples. Experiments show that we achieved up to 224% speedup in Light Field generation for relative simple scenes like the Cornell Box, and about 100% speed up for complex scenes like the Conference Room and the Sponza Palace.