應用版畫色序法實現高畫質低功率之節能液晶顯示器

Abstract

全球化的氣候異常變遷已被公認為近年來最重要的環保問題，面對這樣的窘境，開發且廣泛使用節能家電用品成為讓地球永續發展的重要一環。有鑑於電視相關顯示產品的用電量約佔家用電的百分之十，因此，本論文除了提升顯示器的影像品質外，更朝向低耗能的環保液晶顯示技術發展。 本論文將液晶顯示器視為一組雙面板的顯示架構，包含一個高解析度的液晶面板與一個可獨立調變光強度且由發光二極體 (LED) 組成的低解析度背光面板。在此雙面板的架構下，分為兩個階段針對背光及液晶兩面板提出不同於先前的方法，進一步提升高動態範圍 (high dynamic range, HDR) 及色序型 (field-sequential color) 兩大顯示技術的顯像品質。 首先，在第一階段針對背光部分，提出IMF (Inverse of a Mapping Function) 背光決定法。IMF可依據不同輸入影像，演算出符合該畫面特性的動態背光映對函數 (mapping function)。從實驗結果發現，利用IMF背光決定法，除了提升液晶顯示器的對比度外，在維持與傳統液晶顯示器相同的最高亮度下，更大幅降低30%的電能消耗。 在第二階段部分，由於色序型液晶顯示器在不需要彩色濾光片的情形下，可提升三倍的光使用率以進一步降低電能消耗，但色序型顯示器確有著致命的潛在缺陷：色分離現象。此缺陷將大幅降低影像品質，甚至造成人眼觀看時的不舒適感，因此提出優化無彩色濾光片液晶面板的方法。不同於先前需要超過300Hz的子畫面更新頻率，我們提出低於240Hz的版畫概念色序型液晶顯示技術 (Stencil-FSC) 來抑制色分離現象並巧妙的將高動態範圍技術應用於傳統的色序型顯示技術。如同版畫技巧，Stencil-FSC先將三原色的影像內容初步集中於第一個子畫面，如此一來，可大幅降低剩下各子畫面的亮度，僅用來補足第一個子畫面顯示不足的顏色。經由80張不同影像內容的模擬結果，色分離平均抑制量為傳統色序型顯示器的50%，從實際的拍攝結果也幾乎察覺不出色分離現象。 最後，我們將Stencil-FSC的概念硬體實現於32吋的色序型液晶顯示器。實驗量測結果顯示其不僅提升影像對比至26,000:1、114% NTSC的色域表現，同時，更大幅降低平均電能消耗至35瓦特以下，相當於傳統同尺寸LED背光液晶顯示器耗電量的20%。在如此低耗能高品質的顯示技術下，期許未來人類在與親朋好友享受高品質多媒體影像的同時，也能為地球的永續發展盡一分心力。

Climate change is now widely recognized as a major environmental problem. In creating a sustainable world, energy-efficient household electronics should be developed and popularized. Since TV-related activity occupies 10% of overall household power usage, developing high image performance and low power consumption “Eco-LCDs” becomes the main subject in this dissertation. An LCD was studied as a dual-panel structure: a low resolution controllable LED backlight and a high resolution LC panel. Based on this dual-panel concept, we divided this dissertation into two stages and proposed novel methods to improve both high dynamic range (HDR) and field-sequential color (FSC) technologies. In the first stage, we proposed the IMF method to optimize HDR-LCD backlight signals. IMF provided a dynamic backlight gamma to achieve high contrast ratio and high brightness images while reducing average power consumption by 30% when compared to the same size LED backlight LCD. Furthermore, an FSC-LCD enhanced the optical throughput by a factor of 3 because of getting rid of color filters. However, the FSC-LCD is still facing a lethal issue, color breakup (CBU). In the second stage, we proposed the Stencil-FSC method at less than 240Hz field rate to suppress CBU. This method was much different from the prior CBU suppression methods which usually used field rate more than 300Hz. Stencil-FSC ingeniously applied local HDR technology to an FSC-LCD. The originality of Stencil-FSC was to use a multi-color image concentrating image luminance in a single field. The intensities of the residual primary-color sub-frames were therefore greatly reduced. Through simulations, CBU was suppressed by 50% for eighty test images when compared to conventional RGB-driving and made CBU almost imperceptible in experimental photos. In addition, this dissertation successfully demonstrated the Stencil-FSC method on a 32-inch FSC-LCD to yield a high dynamic contrast of 26,000:1, a wide color gamut of 114% NTSC, and average power consumption of less than 35 Watts which was equivalent to 20% of the same size full-on LED backlight LCD. In the future, we expect that human beings will enjoy high quality multimedia with families or friends and simultaneously maintain a healthy Earth.