摘要
薄膜電晶體液晶顯示器(Thin Film Transistor Liquid Crystal Display, TFT-LCD)，由於兼具輕薄、重量輕、不佔空間方便攜帶等優點，讓許多更方便、更小型之攜帶式電子產品不斷被發展問世，但液晶顯示器本身不自發光，需要靠一強大的背光源才可讓影像呈現，而這強大的背光源便成為液晶顯示器耗電的兇手，降低背光光源雖然可以減少能源上的消耗，可是卻會影響顯示的品質。本篇論文針對此問題提出兩項改善方式：動態背光亮度控制(Dynamic backlight control)以利降低背光的耗電量、Gamma補償法(Gamma compensation)維持影像前後品質。降低背光模組亮度是使用脈波寬度調變方式(PWM dimming control)，用以控制發光二極體驅動晶片(LED driver IC)的致能腳位(EN pin)，藉由脈波寬度責任週期(duty cycle)ON/OFF比例的不同，達到控制背光亮暗比例，進而獲得不同之背光亮度呈現。Gamma影像補償法是利用液晶顯示器於顯示上需要調整影像與亮度輸出符合Gamma曲線(一般來說Gamma為2.2)，該曲線為各灰階對應亮度所繪製，當然也同樣可利用該曲線推導出當背光亮度下降時，不同的灰階階調下該如何做出適當修正，使其整體影像不至於改變太多。通常進行影像處理時，都較需要有強大之CPU(Central Processing Unit)以及記憶體，使其儲存大量之影像資料加以分析比對，縮短演算時間。本論文系統設計則是以“元件可程式化邏輯閘陣列”(Field Programmable Gate Array, FPGA) 為硬體核心，搭配發光二極體驅動電路所組成，同時將Gamma 補償演算法各灰階對應之數據使用查表(look-up table, LUT)的方式建立於FPGA中，如此一來便可以即時對應出各階影像輸入與輸出所需補償的數據，非常適合用在即時性系統(Real-time system)。

關鍵字：動態背光控制、影像資料補償

Abstract
Thin Film Transistor Liquid Crystal Display, abbreviated as TFT LCD, is featured by its light, thin and portable characteristics. By virtue of these advantages, a number of electronic products of such characteristic are under development to launch. Nonetheless, the LCD module does not illuminate itself. It needs using a powerful backlight to show the image, which is the leading factor of the power consumption. Dimming the backlight can doubtlessly save energy, yet it degrades the quality of image. Two solutions to this issue are proposed in this paper, including Dynamic backlight control for reducing power consumption of backlight and Gamma Compensation for maintaining the quality of images. Backlight module control technique is used PWM dimming control method that is adopted to control the EN pin of LED driver IC. By means of the various rate of PWM duty cycle, the illumination of backlight can be controlled.Gamma compensation technique is utilized to refine the quality of image. It takes the advantage of Gamma 2.2 curve, inputting gray code to make proper adjustments when the backlight is dimmed.By and large, images processing requires large CPU and Computer memory to curtail the calculating time as well as saving a large amount of image data for analyzing. Our system is constructed by FPGA which is the core of compensation algorithm system and the backlight is control by LED driving circuit. In this system it didn’t had the powerful CPU can calculation the large of image data. So the LUT method is be used. It is easy to setting as also applied to build the compensation in FPGA. By this manner, the compensation of input and output of all image levels can be instantly obtained and it suits rather well the Real Time System.

Keyword：Dynamic backlight control、Image data compensation

參考文獻
[1]戴亞翔， TFT-LCD面板的驅動與設計，五南圖書出版社，2006。
[2]陳秋雲，e 世代液晶顯示器，全華科技圖書。
[3]陳德請，近代光學顯示工程導論，全華科技圖書。
[4]鄭信源，Verilog 硬體描述語言數位電路，儒林出版社，2005。
[5]黃英睿、黃稚存，Verilog 硬體描述語言，全華科技圖書，2005。
[6]N. Chang, “DLS: dynamic backlight luminance scaling of liquid crystal display,” IEEE Trans. on Very Large Scale Integration Systems, pp.837-846, Aug. 2004.
[7]W.-C. Cheng, “Power minimization in a backlit TFT-LCD display by concurrent brightness and contrast scaling,” IEEE Trans. on Consumer Electronics, pp.25-32, Feb. 2004.
[8]H. Cho, “A backlight dimming algorithm for low power and high image quality LCD applications,” IEEE Trans. on Consumer Electronics, pp.839-844, May 2009.
[9]C. Lai and C. Tsai, “Backlight power reduction and image contrast enhancement using adaptive dimming for global backlight applications,” IEEE Trans. on Consumer Electronics, pp.669-674, May 2008.
[10]L. Kerofsky and S. Daly, “Brightness preservation for LCD backlight reduction,” SID Int’l Symposium Dig. Tech., pp. 1242-1245, 2006.
[11]A. Iranli, W. Lee, and M. Pedram, “HVS-aware dynamic backlight scaling in TFT LCD,” Dept. of Electrical Engineering University of Southern California Los Angeles.
[12]W.-C. Cheng and Y. Hou, “Power minimization in a backlit TFT-LCD display by concurrent brightness and contrast scaling,” Department of EE-Systems, University of Southern California Los Angeles.
[13]M. Anandan, “LED backlight: enhancement of picture quality on LCD screen,” Organic Lighting Technologies.
[14]LED產業網 http://www.ledinside.com.tw/what_is_led
[15]友達光電技術專區 http://auo.com/auoDEV/technology.php?sec=tftIntro&ls=tc
[16]奇美光電官網 http://www.chimei.com.tw/index.asp
[17]億光電子 http://www.everlight.com/
[18]維基百科 – 液晶特性 http://zh.wikipedia.org/zh/%E6%B6%B2%E6%99%B6
[19]背光模組介紹 http://www.or.com.tw/mz/down_mz_2/down_mz_2-b-27.htm
[20]楊孫成，用於適應環境光亮度的影像處理方法，國立臺灣科技大學電機 工程研究所，碩士論文，2005。
[21]陳水萍，液晶顯示器影像色彩迦瑪曲線調整機制之研究，國立臺灣科技 大學自動化及控制研究所，碩士論文，2006。
[22]李界磐，以影像亮度為基礎之適應性影像增強法的研究，國立臺灣科技 大學電機工程研究所，碩士論文，2005。
[23]紀肇育，以分水嶺演算法為基礎之彩色影像切割，國立成功大學電機工 程學系，碩士論文，2004。
[24]張志豪，LED用於背光模組之發展與散熱問題，工研院材化所，工業材料雜誌247 期，2007。