Dimming Technique Research Articles

High Power-Saving and Fidelity-Aware Hybrid Dimming Approach for an LED BLU-Based LCD

Backlight dimming techniques have been researched much to obtain high power saving on display modules, especially those which are based on LCD. The use of LED as a light source in a backlight module has opened a wider chance to perform local dimming as an improvement of a conservative global dimming approach. However, local dimming techniques are sometimes observed to obtain worse performance than global dimming ones in terms of power saving or image fidelity. We observed that even some of their results show visible artifacts. In this paper, we propose a novel backlight dimming technique called hybrid dimming, which combines local and global dimming approaches effectively. We do local dimming to obtain the initial backlight levels while calculating its SSIM index, which is a human visual system-aware image quality metric. We then make sure that these backlight levels don't exceed the ones obtained from a human visual system-aware global dimming with similar image fidelity. As a result, our proposed method can gain better power saving than a human visual system-aware global dimming and prior local dimming techniques, while making little difference in the image fidelity and suppressing visible block artifacts in the results. Experimental results showed that the proposed technique can achieve up to 14, 2.2, and 2.4 times higher power saving ratio than human visual system-aware global dimming and two well-designed local dimming techniques, respectively.

A Novel Adaptive Dimming LED Backlight System With Current Compensated X-Y Channel Drivers for LCD TVs

In this paper, a novel two-dimensional adaptive dimming and current compensation technique with X-Y channels for light-emitting diode (LED) backlight system in LCD TVs is proposed . The proposed LED backlight has matrix structured LED modules with row and column switches to control the brightness of individual division block. It shows local dimming effects such as reduced power consumption and high dynamic contrast ratio even with much less number of LED drivers than that of the conventional two-dimensional local dimming method. Therefore, low cost and compact design of LED drivers can be achieved. This paper also contains a new adaptive dimming algorithm and image compensation technique for the proposed LED backlight system. Moreover, luminance difference among blocks caused by different I-V characteristics of LED and the luminance variation caused by temperature change are compensated by current sensing system. The proposed dimming technique is verified by simulation and experimental results based on a RGB-LED backlight of a 32-inch LCD TV.

A Novel Dimming Technique for Cold Cathode Fluorescent Lamp

In this paper, a simple dimming control is presented and applied to a cold cathode fluorescent lamp (CCFL). Traditionally, the digital dimming takes back-and-fro start and cutoff of the CCFL, thereby causing current spike and hence reducing the life of the CCFL. Consequently, to overcome these problems, a dimming strategy is presented according to the frequency shift. Moreover, a full-bridge phase-shift resonant inverter is utilized to power the CCFL. Some experimental results are provided to demonstrate the effectiveness of the proposed scheme.

Pseudo Zero-Dimension Dimming for Power Reduction in Field Sequential Color Liquid Crystal Display Systems

Expensive hardware is required by the conventional two-dimensional (2-D) light-emitting diode (LED) dimming technique to obtain high-contrast and low-power in the field sequential color (FSC) technique. Thus, based on real-time image data, the pseudo zero-dimension (0-D) LED dimming technique is proposed to further reduce power dissipation in the D-FSC technique, which allows the intelligent selection of an adequate color sequence. The multi-liquid crystal and backlight (LC/BL) algorithm utilizes the D-FSC technique in temporal and spatial domains. It not only utilizes the pseudo 0-D technique to effectively reduce the color breakup (CBU) effect without greatly increasing frame rate, but also to reduce power consumption. On the backlight module, CBU suppression can be substantially improved and power dissipation can be reduced by at least 12.5%. Power consumption can also be further reduced through the re-dimming improvement in the proposed pseudo 0-D dimming technique.

22.3: Quantified Evaluation for Clipping Artifact of Local Dimming in LCDs

AbstractClipping is one of the most annoying artifacts caused by pixel compensated local dimming technique in LCDs. Severe clipping artifact will reduce image local contrast and erase texture details. This paper proposes some quantified method for evaluating the severity of clipping artifact. The proposed evaluation method can be carried out easily by using some designed patterns and simple counting method.

A High-Efficiency Dimmable LED Driver for Low-Power Lighting Applications

This paper presents a dimmable light-emitting diode (LED) driver with adaptive feedback control for low-power lighting applications. An improved pulsewidth modulation dimming technique is studied for regulating the LED current and brightness. Under universal input voltage operation, high efficiency and high power factor can be achieved by a coupled inductor single-ended primary inductance converter power factor correction (PFC) converter with a simple commercial transition-mode PFC controller. The operation principles and design considerations of the studied LED driver are analyzed and discussed. A laboratory prototype is also designed and tested to verify the feasibility.

Reduction of Image Degradation due to Viewing Angle in Adaptive Dimming Technique

An adaptive dimming technique controls both LCD panel transmittance and its backlight luminance adequately and locally according to the input TV signal. The technique reduces the power consumption and also improves the picture quality. However, a steep change in backlight luminance distribution due to the application of the technique causes image degradation around the boundary of the segments when the LCD is viewed from an angle. The main factor of image degradation is the illumination of a pixel by neighboring pixel's corresponding backlight when the LCD is viewed from an angle rather than normal direction. From the subjective evaluation of image quality and computer simulation, it is found that the gradient of the backlight luminance variation to luminance at the border of the segment should be less than 0.022 per pixel in order to suppress the image degradation.

Magnetically-controlled dimming technique with isolated output

New advances on magnetically-controlled electronic ballasts can grant the ability to dim the lamp and simultaneously guarantee output electrical isolation. By means of a variable transformer, the model of which is presented, this new technique is developed and experimentally verified. In addition, a simple method for the large signal characterisation of the transformer is described. An FH 14W/840 Osram lamp was chosen to validate this new technique and experimental results clearly show its adequate behaviour.

24.3: Evaluation of LCD Backlight Local Dimming System

AbstractBacklight local dimming technique can improve the static contrast and reduce power consumption of LCDs significantly. Several backlight local dimming systems have been reported in previous literatures. However, there is still no comprehensive description about the evaluation of various backlight local dimming systems. This paper tries to make a guideline for evaluating contrast, power consumption and image quality of backlight local dimming system.

Mitigating energy wastage of light-emitting diodes using discretised multilevel pulsation

There is a recent trend and growing popularity of using the technique of light pulsation for achieving the dimming control of light-emitting diodes. However, it is found that such a dimming control technique can result in a significant power loss in terms of luminous efficacy. This contradicts the original motive of energy saving through illumination dimming. Total energy consumed for lighting is an overwhelming 8% of depleting energy resources. A potential loss of 2% or more of these resources could go unnoticed owing to poor handling of dimming technology. It is demonstrated that, driving the LEDs with discretised multilevel pulsation, can achieve a quasi-optimally-efficient state of dimming control with a saving of up to 26.7% of the luminous efficacy.

A Novel Two-Dimensional Adaptive Dimming Technique of X-Y Channel Drivers for LED Backlight System in LCD TVs

In this paper, a novel two-dimensional (2-D) adaptive dimming technique with X-Y channels for light-emitting diode (LED) backlight system in LCD TVs is proposed. The proposed LED backlight has matrix-structured LED modules with row and column switches to control the brightness of individual division block. It shows local dimming effects such as reduced power consumption and high dynamic contrast ratio even with much less number of LED drivers than that of the conventional 2-D local dimming method. Therefore, low cost and compact design of LED drivers can be achieved. This paper also contains a new adaptive dimming algorithm and image manipulation technique for the proposed LED backlight system. The proposed dimming technique is verified by simulation and experimental results based on a RGB-LED backlight of a 32-in LCD TV.

Design and implementation of a digital control IC for driving multiple cold cathode fluorescent lamps

AbstractThis study designs and develops a digital control integrated circuit (IC) for driving circuits operating multiple cold cathode fluorescent lamps (CCFLs). The control IC adopts an external crystal oscillator for the IC's external frequency to provide the driving circuits a fixed frequency. Inside the IC, two control loops are designed, under synchronized operation frequencies, for a boost regulator and an inverter. The main function of the boost regulator control loop is to supply a steady DC voltage for the inverter. In designing the inverter's control circuit, an adjustable‐frequency adjustable‐voltage soft‐start technique is used to start the lamps. We also use burst mode digital dimming technique to achieve synchronized dimming for the parallel‐connected lamp‐ignition circuits. The feedback voltage from the CCFLs can determine if any lamp is abnormal via a proposed lamp abnormality detection circuit. To deal with the equivalent‐circuit's component parameter differences among various manufacturers' and brands' piezoelectric transformers (PTs), the inverter's operation frequency is designed fine‐tunable in this study. Finally, the proposed design concept was implemented with an actual control IC and a driving circuit for CCFLs. The measured data and waveforms from our test circuitry are presented, which verifies the validity of the miniaturized controller proposed in this study. Copyright © 2008 John Wiley & Sons, Ltd.

アダプティブディミング方式を用いたLCDの階調特性改善(画像技術,視覚・画質関連,その他一般)

アダプティブディミング方式を用いたLCDの階調特性改善(画像技術,視覚・画質関連,その他一般)

Understanding structures at the base of the solar corona – polar plumes

AbstractRecent work on coronal polar plumes (Gabriel et al. 2003, 2005) has aimed at determining the outflow velocity in plume and interplume regions, using the Doppler dimming technique on oxygen VI observations by SUMER and UVCS on SOHO. By comparing observations of SOHO/EIT with plume modelling, we show that the major part of plumes is the result of chance alignments along the line-of-sight of small enhancements in intensity. This confirms the so-called curtain model. These plumes can be attributed to reconnection activity along the boundaries of supergranule cells. A second population of plumes has a lower abundance and arises from surface bright points having a particular magnetic configuration. New observations using the Hinode/EIS spectrometer are in progress, with the aim of providing further insight for this model.

Backlight power reduction and image contrast enhancement using adaptive dimming for global backlight applications

The paper presents an adaptive dimming technique to reduce backlight power consumption and enhance image contrast for global backlight applications. The proposed adaptive dimming technique consists of two new algorithms: backlight dimming algorithm and contrast enhancement algorithm. The backlight-dimming algorithm obtains appropriate 0% to 50% backlight power reduction depending on characteristics of the image data. The contrast enhancement algorithm not only reduces the adverse effect of backlight power saving, but also improves 20.75% enhancement of image contrast ratio on the average. Numerous simulation results are used for illustration of the effectiveness and merits of the proposed adaptive dimming technique. Experimental results are conducted to show the performance and usefulness of the proposed technique on a 2.2-inch mobile phone liquid crystal display (LCD) made by thin-film-transistor (TFT) technology.

Power savings and enhancement of gray‐scale capability of LCD TVs with an adaptive dimming technique

Abstract— The luminance of a backlight unit for an LCD TV is adaptively and locally dimmed along with the input video signal in order to reduce the power consumption and also to improve the picture quality. By adopting the zero‐dimensional (0D), 1D, and 2D adaptive dimming techniques, a sample movie having 8.0% post‐gamma average picture levels (APL) could be displayed using 83%, 71%, and 50% of the original backlight power, respectively. For an adoption of the 2D dimming, an LED backlight is preferable. The adaptive‐dimming technique also allows the differential aging characteristics between the LED components and temperature dependence of color and luminance to be overcome. From simulations of a reduction in power consumption, it was found that 40 × 40 pixels is a unit of the local dimming, 30 frames for the sampling period, 24 dimming steps, and an equal‐signal‐step method for determining the dimming factor have been found to be appropriate. The gray‐scale capability of low‐luminance images can also be improved by dimming the backlight luminance and expanding the input signal. By using an LCD TV having an 8‐bit capability, an 11‐bit‐equivalent gray‐scale expression was experimentally proven.

Dimming self-oscillating ballast by variable inductor

A simple new dimming technique for self-oscillating electronic ballasts based on a variable inductance is introduced. The variable inductor is controlled by DC current. The goal is to keep the resonant condition during dimming without utilising any IC or complex control circuits. Dimming is successfully accomplished and theoretical and experimental results are presented on self-oscillated current fed push pull electronic ballast.

Electronic ballast for multiple fluorescent lamp systems

An electronic ballast for multiple tubular fluorescent lamp systems is presented. The proposed structure has a high value for the power factor, a dimming capability, and soft switching of the semiconductor devices operated at high frequencies. A zero-current switching pulse width modulated SEPIC converter is used as the rectifying stage and it is controlled using the instantaneous average input current technique. The inverting stage consists of classical resonant half-bridge converter with series-resonant parallel-loaded filters. The dimming control technique is based on varying the switching frequency and monitoring the phase shift of the current drained by the filters and lamps in order to establish a closed loop control. Experimental results are presented that validate the theoretical analysis.

Solar Wind Outflow in Polar Plumes from 1.05 to 2.4 R ⊙

An earlier publication (Paper I), which measured the outflow velocity in solar plumes out to 1.35 R☉ using the Doppler dimming technique, has here been extended out to 2.4 R☉ by including observations from SOHO UVCS. It is shown that plume outflow velocities, greater than interplumes at lower heights, have lower acceleration and fall below interplume velocities at heights greater than 1.6 R☉. This analysis resolves what has been an apparent disagreement between previously published work. The mass flow rate in plumes is shown to decrease with height, presumably through mass transfer to the interplume regions.

An Analysis Into the Dimming Control and Characteristic of Discharge Lamps

This paper provides some qualitative insights into, and a quantitative analysis of, the interrelationship between the ballast circuit parameters and the physical processes inside the lamp arc under dimming conditions. Qualitative explanation is supported by experimental observations on the dimming characteristics of fluorescent and high-intensity-discharge (HID) lamps. This understanding enables engineers to choose the right combination of dimming technique and electronic ballast topology for different types of discharge lamps. Verified by experiments, the fundamental approximation technique is used to characterize the frequency-control and voltage-control dimming technique for series-loaded and parallel-load resonant circuits.