Backlight Dimming Research Articles

A Survey of Low-power Techniques for Liquid Crystal Display Systems with Light Emitting Diode Backlight Units

As the technology evolves, end-users are stuffed with many kinds of handheld devices along with an enor-mous number of interactive multimedia applications and communication functionalities. These devices con-sume much power, especially for displaying their services or functions. In contrast, the battery, which is the main power supplier for such devices, has a much lower capacity growth compared to the power demands. This gap has inspired many researchers to study low-power display techniques. In the mean time, there came the invention of a light emitting diode (LED) as a new backlight source for a display panel. LEDs have been adopted in the most widely used Liquid Crystal Display (LCD) system. This paper focuses on recent noticeable low-power display techniques based on LCD systems, especially associated with an LED back-light unit as its light source. We categorize these techniques into four groups: 1) low-power techniques with backlight dimming, 2) low-power techniques with dynamic voltage scaling, 3) software-based low-power techniques, and 4) hardware-based low-power techniques, and review the core of each technique briefly. Among many techniques, concurrent brightness and contrast scaling technique in a color sequential LED-backlit display system achieved the largest power saving ratio by up to 90% of the total system power with a small distortion level. As future research, it is one of important methods to combine the pros from each beneficial technique into one synergistically in the aspect of the whole system power.

P‐53: Dynamic Backlight Control Method for RGBW LCD

AbstractIn this paper, we develop a system for adaptively adjusting the backlight luminance enabling extreme power reduction. Tools to maintain primary color brightness and saturation are described. Using the proposed system, RGBW color and backlight dimming can be appropriately managed. This novel technology was successfully implemented in our 10.1″ checkerboard RGBW LCD.

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.

Advanced Methods for Field‐Sequential‐Color LCDs with Associated Power Reduction Advantages

Using stencil‐field‐sequential‐color methods with field rates as low as 120 Hz in conjunction with local color backlight dimming can effectively suppress color break‐up. With the addition of a color‐filterless LCD with an intelligent LED backlight and a non‐polarized LC cell, optical throughput can be increased by a factor of 10, while at the same time requiring a lower material cost/count, resulting in an environmentally friendly display.*

Backlight power reduction using efficient image compensation for mobile devices

Since backlight dimming widely used for power reduction of mobile devices degrades the image quality in brightness and contrast, image enhancement is exploited to compensate the degradation. In this paper, we propose a novel backlight power reduction scheme using an efficient image compensation algorithm that scales discrete cosine transform (DCT) coefficients of image in the compressed domain. To reduce the computational burden of the conventional backlight dimming method where decompression is performed prior to image compensation in the spatial domain, we introduce a computationally efficient image compensation algorithm that processes only dominant DCT coefficients of images using a mapping function in the DCT domain. Experimental results indicate that our proposed method provides higher visual quality with reduced complexity as compared to conventional image compensation schemes.

67.3: Low Power Liquid Crystal Displays Using an Image Integrity‐based Backlight Dimming Algorithm

AbstractThis paper presents a new backlight dimming approach using dynamic gray‐level error control in liquid crystal displays. The existing methods using the fixed rate of clipped pixels degrade the image quality seriously for some images even after image compensation. The proposed method dynamically chooses the maximum luminance based on image integrity considering image characteristics. Therefore, it preserves the image quality above any desired level, while reducing power consumption as much as possible.

P‐79: HSP: A Hybrid Simulation Platform for Backlight Dimming in TFT‐LCDs

AbstractA general and comprehensive hybrid simulation platform(HSP) is developed for conveniently evaluating and optimizing the backlight design and driving schemes in TFT‐LCDs to achieve low power and excellent image quality. It incorporates a range of capabilities from the early backlight optical simulation to the performance evaluation and optimization at the system level for the design of almost all kinds of LCD backlight systems. The HSP is then used to optimize and evaluate a local dimming scheme based on edge‐type LED backlight technology for a 14.1′W TFT‐LCD panel, and the simulation and analysis results are presented.

P‐193L: Late‐News Poster: Optimized Local Dimming Solution in IPS‐mode LCD Technology

AbstractHigh contrast ratio and low power consumption for LCDs with LED BLU can be obtained by backlight local dimming with pixel compensation while maintaining image brightness. This technique can greatly increase the contrast ratio of IPS‐mode LCDs. The technique, however, suffers from the side effects called flicker, halo, clipping, and non‐uniformity. The intensity of the side effects is proportional to the amount of the local dimming applied. This paper presents a noble local dimming algorithm which adaptively determines the amount of backlight dimming by characteristics of each block in each scene and feedback values to maximize contrast ratio and power consumption saving effect without noticeable side effects. The experimental results of the proposed algorithm are shown along with those of conventional algorithms.

Adaptive Backlight Dimming for LCD Systems

Dimming technology has evolved dramatically over the last several years and is now enabling innovations in many LCD‐based products such as TVs and monitors, which must continue to improve in terms of picture quality and energy efficiency while remaining cost effective. Although dimming is valuable for both CCFL and LED backlighting applications, it can be used most effectively with LED light sources. This article also discusses some innovative edge‐lighting dimming solutions.

ディスプレイ―ＩＤＷ’０８を中心に―バックライト輝度とガンマ変換関数の同時最適化による高コントラスト・低消費電力液晶ディスプレイ

In recent years, liquid crystal displays (LCDs) are being increasingly used in various display products, such as cellular phones and televisions, leading to demands for higher image quality and lower power consumption. The contrast ratio of LCDs is, however, lower than that of emissive displays such as organic light-emitting diode ones. A novel algorithm for LCD backlight dimming to improve the contrast ratio of LCDs is proposed. Backlight luminance and a gamma conversion function are simultaneously optimized acording to input images by minimizing the sum of squared difference between the ideal gamma characteristic with an infinite contrast ratio and the LCD gamma characteristic with a finite contrast ratio. Furthermore, LCD prototypes that utilized the proposed algorithm were developed, and they had both a high contrast ratio and low power consumption.

2-6 領域別バックライト輝度制御LCDにおける最適領域発光プロファイルの検討(第2部門 ディスプレイ)

2-6 領域別バックライト輝度制御LCDにおける最適領域発光プロファイルの検討(第2部門 ディスプレイ)

Focus on sensors

Focus on sensors

64.2: Spatio‐temporally Consistent Video Processing for Local Backlight Dimming

AbstractLocally addressable backlights allow the contrast of LCDs to be improved while simultaneously reducing power consumption. for optimal performance, the associated video processing algorithms should prevent the backlight structure from appearing in the front‐of‐screen (FOS) image. We present several algorithmic developments that improve the spatio‐temporal consistency of the backlight image and prevent clipping in the panel, thus substantially improving the FOS performance.

Locally pixel‐compensated backlight dimming on LED‐backlit LCD TV

Abstract— The pixel brightness of an LCD panel perceived by a user is the product of the backlight brightness and the panel transmittance. In conventional LCD panels, the backlight brightness is constant and always at peak luminance. This design suffers from light leakage and power waste problems at dark scenes. This paper presents a new LCD system, which uses locally pixel‐compensated backlight dimming (PCBD). The proposed method combines backlight control and pixel processing for reducing light leakage and power consumption while keeping the image at the original brightness. Backlight luminance is dimmed locally in the dark‐image region, and pixel values are compensated synchronously according to the luminance profile of dimmed backlight. By reducing the light leakage, a static contrast of over 20,000:1 has been achieved on a large‐sized LCD panel with the proposed PCBD method. No obvious artifacts have been noticed as well. The power consumption of the panel can also be greatly reduced, depending on various video content. The PCBD method could be widely used for developing state‐of‐the‐art LCD panels with LED backlights.

39.3: Locally Pixel‐Compensated Backlight Dimming for Improving Static Contrast on LED Backlit LCDs

AbstractThis paper presents a pixel compensated backlight dimming method for improving contrast on LED‐LCD. The backlight luminance is dimmed locally along with image contents, and pixel values are compensated synchronously according to the luminance profile of dimmed backlight. Static contrast above 20000:1 has been achieved on a large size LCD with the proposed method and no obvious artifacts are observed.

Quality-Based Backlight Optimization for Video Playback on Handheld Devices

For a typical handheld device, the backlight accounts for a significant percentage of the total energy consumption (e.g., around 30% for a Compaq iPAQ 3650). Substantial energy savings can be achieved by dynamically adapting backlight intensity levels on such low-power portable devices. In this paper, we analyze the characteristics of video streaming services and propose a cross-layer optimization scheme called quality adapted backlight scaling (QABS) to achieve backlight energy savings for video playback applications on handheld devices. Specifically, we present a fast algorithm to optimize backlight dimming while keeping the degradation in image quality to a minimum so that the overall service quality is close to a specified threshold. Additionally, we propose two effective techniques to prevent frequent backlight switching, which negatively affects user perception of video. Our initial experimental results indicate that the energy used for backlight is significantly reduced, while the desired quality is satisfied. The proposed algorithms can be realized in real time.

HVS-Aware Dynamic Backlight Scaling in TFT-LCDs

Liquid crystal displays (LCDs) 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 the handheld device which is responsible for about half of the 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 lifetime. 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 inter-frame (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

26.4: Algorithm for Contrast Reserve, Backlight Dimming, and Backlight Boosting on LCD

This paper presents an algorithm for controlling the signals to an LCD panel and its backlight. The objective is to maximize the signal to the display and to perform the dynamic backlight dimming very effectively. Then the average power can be limited, e.g. to 500 cd/m2 average screen brightness, and on occasional bright scenes the backlight can be boosted significantly, e.g. to 800 cd/m2 peak screen brightness during a few minutes.

26.2: Distinguished Paper: Brightness Preservation for LCD Backlight Reduction

Backlight dimming is the predominant method for power reduction in LDC displays and image processing can compensate for such dimming. We propose a low complexity approach which replaces hard clipping with smooth roll-off. A high quality approach preserves highlight detail. Image quality is improved and power savings can be increases by more aggressive BL dimming capable with these methods.

Brightness preservation for LCD backlight dimming

Journal of the Society for Information DisplayVolume 8, Issue 1 p. 1-1 Introduction Andras I. Lakatos, Andras I. Lakatos EditorSearch for more papers by this author Andras I. Lakatos, Andras I. Lakatos EditorSearch for more papers by this author First published: 18 June 2012 https://doi.org/10.1889/1.1828693Citations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume8, Issue1March 2000Pages 1-1 RelatedInformation