Transmittance Scaling for Reducing Power Dissipation of a Backlit TFT-LCD

Cheng, Wei‐Chung; Pedram, Massoud

doi:10.1007/1-4020-8076-x_10

Cited by 4 publications

(2 citation statements)

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“…Therefore, we model the CCFL illumination as a function of the driving current only and ignore the other parameters. Accounting for the saturation phenomenon in the CCFL light source [29], we use a two-piece linear function to characterize the power consumption of CCFL as a function of the backlight factor:…”

Section: Iva Hardware Characterization Iva1 Cold Cathode Fluorescementioning

confidence: 99%

HVS-Aware Dynamic Backlight Scaling in TFT-LCDs

Iranli

Lee

Pedram

2006

IEEE Trans. VLSI Syst.

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Liquid Crystal Displays have appeared in applications ranging from medical equipment to automobiles, gas pumps, Laptops and handheld portable computers. These display components present a cascaded energy attenuator to the battery of handheld device which is responsible for about half of energy drain at maximum display intensity. As such, the display components become the main focus of every effort for maximization of embedded system's battery life-time. This paper proposes an approach for pixel transformation of the displayed image to increase the potential energy saving of the backlight scaling method. The proposed approach takes advantage of human visual system (HVS) characteristics and tries to minimize distortion between the perceived brightness values of the individual pixels in the original image and those of the backlight-scaled image. This is in contrast to previous backlight scaling approaches which simply match the luminance values of the individual pixels in the original and backlight-scaled images. Furthermore, this paper proposes a temporally-aware backlight scaling technique for video streams. The goal is to maximize energy saving in the display system by means of dynamic backlight dimming subject to a video distortion tolerance. The video distortion comprises of (1) an intra-frame (spatial) distortion component due to frame-sensitive backlight scaling and transmittance function tuning and (2) an interframe (temporal) distortion component due to large-step backlight dimming across frames modulated by the psychophysical characteristics of the human visual system. The proposed backlight scaling technique is capable of efficiently computing the flickering effect online and subsequently using a measure of the temporal distortion to appropriately adjust the slack on the intra-frame spatial distortion, thereby, achieving a good balance between the two sources of distortion while maximizing the backlight dimming-driven energy saving in the display system and meeting an overall video quality figure of merit. The proposed dynamic backlight scaling approach is amenable to highly efficient hardware realization and has been implemented on the Apollo Testbed II. Actual current measurements demonstrate the effectiveness of proposed technique compared to the previous backlight dimming techniques, which have ignored the temporal distortion effect.2

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Section: Iva Hardware Characterization Iva1 Cold Cathode Fluorescementioning

confidence: 99%

HVS-Aware Dynamic Backlight Scaling in TFT-LCDs

Iranli

Lee

Pedram

2006

IEEE Trans. VLSI Syst.

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“…Therefore, we model the CCFL illumination as a function of the driving current only and ignore the other parameters. Accounting for the saturation phenomenon in the CCFL light source [10], we use a two-piece linear function to characterize the power consumption of CCFL as a function of the backlight factor: . 0 ( ) .…”

Section: A) Cold Cathode Fluorescent Lamp (Ccfl)mentioning

confidence: 99%

HEBS: Histogram Equalization for Backlight Scaling

Iranli

Fatemi

Pedram

Design, Automation and Test in Europe

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In this paper, a method is proposed for finding a pixel transformation function that maximizes backlight dimming while maintaining a pre-specified image distortion level for a liquid crystal display. This is achieved by finding a pixel transformation function, which maps the original image histogram to a new histogram with lower dynamic range. Next the contrast of the transformed image is enhanced so as to compensate for brightness loss that would arise from backlight dimming. The proposed approach relies on an accurate definition of the image distortion which takes into account both the pixel value differences and a model of the human visual system and is amenable to highly efficient hardware realization. Experimental results show that the histogram equalization for backlight scaling method results in about 45% power saving with an effective distortion rate of 5% and 65% power saving for a 20% distortion rate. This is significantly higher power savings compared to previously reported backlight dimming approaches. IntroductionAs the portable electronic devices become more intertwined with everyday life of people, it becomes necessary to put more functionality into these devices, run them at higher circuit speeds, and have them consume a small amount of energy. These electronic devices are becoming smaller and lighter and often required to operate with fancy Liquid Crystal Displays (LCD's) for increasing periods of time.Unfortunately, the battery capacities are increasing in much slower pace than the overall power dissipation of these kinds of devices. Therefore, it is essential to develop low power design techniques to reduce the overall power dissipation of these devices. Previous studies on battery powered electronic devices have pointed out that the energy consumption in the Cold Cathode Fluorescent Lamp (CCFL), which is the backlight of an LCD, dominates the overall energy consumption of the device [1]. In the SmartBadge system for instance, the display consumes 28.6%, 28.6%, and 50% of the total power in the active, idle, and standby modes, respectively [1]. Unfortunately, as for other resources, one cannot tackle this energy hungry component with some form of power shutdown. This is due to the fact that LCD subsystem must be continuously refreshed and cannot be turned off or put to sleep without a significant penalty in performance and Quality of Service (QoS).There are two main classes of techniques for lowering the power consumption of LCD subsystem. The first class of techniques is focused on the digital/analog interface between the graphics controller and the LCD controller [2] [3]. These techniques try to minimize the energy consumption by taking advantage of different encoding schemes to minimize the switching activity of the electrical bus. For instance, reference [2] uses the spatial locality of the video data to reduce the number of transition on the DVI bus reducing its energy consumption by 75%. More recently, reference [3] has extended the previous work by using the limited intra-word transition...

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