Browsing by Author "Chao, Chain-Fu"

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Minimization for LED-backlit TFT-LCDs
(2006)
Cheng, Wei-Chung
;
Chao, Chain-Fu
;
光電工程學系
;
Department of Photonics
This paper presents an algorithm for minimizing power consumption of LED backlights in transmissive TFT-LCD monitors. The proposed algorithm reduces power consumption by scaling the luminous intensity of the red, green, and blue LED backlights independently according to the image histograms of each color channel. The algorithm consists of two phases. The first phase, chromaticity scaling, finds the optimal ratios of red, green, and blue backlights subject to a perceived color difference constraint. The second phase, luminance scaling, finds the optimal dimming factor subject to a perceived lightness difference constraint. The perceived color and lightness differences are measured by the CIELAB Color Difference Equation 2 Delta E-ab* standard metric for measuring color variation. Psychophysical experiments were performed with 35 observers to uncover the optimal luminance scaling function, An experimental LED backlight module was implemented and installed on a 19" side-lit TFT-LCD monitor to replace the original CCFL backlight. Within limited perceivable difference 2 Delta E-ab*, up to 76% of power consumption can be reduced for the benchmark images.
Temporal vision-guided energy minimization for portable displays
(2006)
Cheng, Wei-Chung
;
Hsu, Chih-Fu
;
Chao, Chain-Fu
;
光電工程學系
;
Department of Photonics
This paper presents a novel backlight driving technique for liquid crystal displays. By scaling the intensity, frequency, and duty cycle of the backlight, this technique not only increases the perceived brightness but also prolongs the service time Of rechargeable batteries. The increased brightness comes from a perceptual effect of temporal vision - a brief flash appears brighter than a steady light of the same intensity, called Brucke brightness enhancement effect. The prolonged service time comes from the relaxation phenomenon - a lithium-ion battery lasts longer by pulsed discharge. Combining these two effects, a great amount of service time can be obtained at the cost of flickering. We performed visual experiments to parameterize the Brucke effect and derived an optimization algorithm accordingly. To demonstrate the potential energy savings of this technique, we profiled the power consumption of an Apple iPod and fabricated an LED driving module. Based on experimental data, 75% of energy consumption can be saved and the service time can be extended to 300%.