Different Backlight Dimming Algorithms for LCD Backlight Power Reduction with Image Quality Enhancement

Abstract

Power consumption and image quality both play important role in liquid-crystal display (LCDs). Compare to cathode ray tubes (CRTs), LCDs have the advantages of being light weight, and having thin format, low radiation and high image quality. However, LCD also has certain disadvantages which need to overcome, such as light leakage from the liquid crystals and non-ideal cross polarization. Using a backlight dimming algorithms can minimize these drawbacks. Although LCDs have high dynamic range properties, the complex algorithm and high cost backlight structure are not suitable for small size LCD products, such as mobiles, PDAs, digital photo frame and Car GPSs. Moreover, due to decrease in the driving current of the back light, the display backlight turns dark. Therefore, we proposed the NIEA algorithm to enhance the image contrast ratio and sustain the quality of image. There has been some research on image contrast enhancement. In Raman and Hekstra proposed an architecture and outlined an algorithm using histogram information of the image for the backlight modulation in LDCs. In Sun and Ruan proposed the dynamic histogram specification algorithm to improve the image contrast. Although the above methods could effectively enhance image contrast, they did not considered image quality for the entire system. In cho and kwon proposed backlight dimmining algorithm to reduce power consumption and improve image quality in LCD applications. In Bartolini and Ruggiero adopted the SSIM method to evaluate image quality from the Human Visual System(HVS). Figure shows the block diagram of our proposed display system for backlight control designed to decrease the power consumption of the LCD backlight and enhance the image contrast to compensate for the image brightness. First, the image data are analyzed to determine whether the TFT LCD back light current increases or decreases. After the backlight dimming level is selected, the system enhances the image contrast based on selected current level, and users almost notice no significant changes in image quality. Both of the proposed new algorithms, New Backlight Dimming Algorithm(NBDA) and New Image Enhancement Algorithm(NIEA), not only decreases power consumption, but also increase image contrast to sustain image quality.