LCD背投影電視顯示屏幕之設計、優化與影像品質評估

Abstract

在背投影式的系統中，顯示屏幕是觀眾最直接觀察到的物件。因此，維持投射出來的影像品質乃是顯示屏幕在設計上最主要的考量。一般常用來評估影像品質的參數有影像的亮度、解析度、對比度等等，然而除了這些參數外，在背投影顯示屏幕上由菲涅耳透鏡、雙凸面透鏡與液晶板這些週期性結構疊加所形成的雲紋花樣（Moire pattern），亦是影響影像品質的重大因素之一。 本論文主要探討顯示屏幕上的雲紋花樣。由於此現象會使人眼在觀賞螢幕時產生不舒服的感覺，因此我們提出藉由螢幕結構間週期的設計來降低雲紋花樣的週期，使雲紋花樣的週期小於人眼可見範圍的方式，以解決此問題。在此，首先說明雲紋花樣的產生原因及分析方式，進而利用「在富氏空間的頻率分析法」，找出菲涅耳透鏡、雙凸面透鏡與液晶板結構間週期比例變化時雲紋花樣週期的變化，並將此關係繪製成圖以應用在「無雲紋花樣螢幕」的設計上。最後利用已設計好的菲涅耳透鏡與雙凸面透鏡的週期規格，配合其他影像參數的需求，設計並優化螢幕的其他的結構參數，並利用光學模擬軟體模擬、分析並驗證此螢幕的影像品質。

Screen is the most direct object of a rear projection system for viewing. Therefore, maintaining the image quality from projection lens is the primary concern in designing a rear projection screen. Brightness, resolution, contrast ratio, and uniformity are among the parameters used in evaluating image quality. Besides, Moire pattern, which would cause uncomfortable feeling while viewing, is also a key point in image quality evaluation. In a LCD rear projection system, Moire pattern is caused by overlapping the periodic structures of LCD, Fresnel lens, and Lenticular lens. The thesis analyzed the Moire pattern of screen and suppressed it by modifying the configuration of the screen. The relationship between the period ratio of each structure and the period of Moire pattern was discussed first by using the spectral analysis method. The occurrence of the Moire pattern was suppressed by achieving the shortest period of Moire pattern. Finally, the image quality of a designed screen was analyzed, then optimized by optical simulation software.