LCD 動態背光控制及色彩補償之系統設計

Abstract

近年來市面上可攜式的消費性電子產品五花八門，且為了符合消費者隨身攜帶的需求，產品的設計也越來越講究輕薄短小；基於這樣的設計需求下，想要增加電池的體積及容量的可能性微乎其微，因此產品的省電設計除了可增加電池的續航力達到環保要求外，同時也是電子產品的致勝關鍵之一；薄膜電晶體液晶顯示器 (Thin Film Transistor Liquid Crystal Display, TFT-LCD) 因具有輕薄、不佔空間等方便攜帶的優點，讓它儼然成為目前最被廣泛使用於視覺產品上的關鍵元件。但因液晶顯示器本身無法自行發光，需要靠強大的背光源經過液晶的折射並穿過彩色濾光片才能讓影像的色彩呈現出來，而整個液晶顯示器模組最耗電的部份便是這強大的背光源，因此要如何減少背光源的耗電，且又該如何補償色彩使其不失畫面顯示的品質，是目前薄膜電晶體液晶顯示器應用上最主要的課題。本篇論文主要應用兩項技術： 1.動態背光亮度控制 (Dynamic backlight control, DBLC) 及 2.色彩補償 (Color compensation) 來改善產品省電環保又兼顧畫質的效能。 本篇論文的系統架構是以可程式化邏輯閘陣列 (Field Programmable Gate Array, FPGA) 為硬體核心電路，利用脈波寬度調變技術 (Pulse width modulation, PWM) 來控制發光二極體背光模組的亮暗度，而色彩補償則是因為當背光亮度減少，為了避免整體畫面變暗，應將影像畫面的資料作補償，讓光線穿過液晶的量增加，使液晶顯示器在顯示各灰階的亮度能符合目前業界標準的 Gamma 2.2 曲線，所以色彩補償技術是利用此曲線為基準，推導出在不同的灰階下，當背光亮度改變時，如何做出適當資料補償修正，使其整體影像維持原始的畫質，並設計成為一個即時 LCD 動態背光控制及色彩補償的系統，達到產品省電環保又兼顧畫質的最終目標。

There are more and more varieties of consumption electronic products in the market in recent years. In order to meet consumer’s needs for portable carrying, the design of product becomes slimmer and smaller. With this design needs and limitation, it is very difficult to increase the volume and capacity of batteries. Therefore, reducing power consumption and increasing battery’s endurance to meet the environmental protection requirements is required as key success factors for products. TFT-LCD (Thin Film Transistor Liquid Crystal Display) can be slim and small which are advantages to achieve portable carrying. TFT-LCD has become the widest application in current visual products in the market. Due to the fact that LCD module cannot illuminate by itself, the image is generated by a powerful backlight which is the key factor of the power consumption. Therefore, how to reduce power consumption and maintain image quality at the same time is the key topic for TFT-LCD application in consumption electronic products. In this paper, two techniques are adopted to improve the performance of products including DBLC (Dynamic backlight control) and Color compensation. The system framework is based on FPGA (Field Programmable Gate Array) for hardware design to reduce power consumption by DBLC and color compensation technique to maintain color quality of images. The illumination of LED (Light Emitting Diode) backlight is controlled by DBLC using PWM (Pulse width modulation) method. Color compensation is used to make an appropriate adjustment when the backlight is dimmed in order to maintain the quality of images. Inputting gray-scale data for color compensation adjustment to meet the Gamma curve 2.2, which is the best standard. These techniques allow achieving power consumption reduction and maintaining color quality of images at the same time in TFT-LCD application.