Local Backlight Dimming Research Articles

79‐1: Invited Paper: Adaptive Local Backlight Dimming Control with Local Boosting

The local backlight dimming (LBD) technology has attracted significant interest for liquid crystal displays. In automotive, notebook PC, and virtual reality applications, LBD should treat the trade‐off between power saving and visual quality enhancement. However, it requires the cost of the high logic complexity to consider the optimal solution at a higher resolution of the image. This paper proposes the adaptive local backlight dimming control, which can reduce the power consumption of backlight and improve the quality of the display. The proposed method analyzes an image contents with a low complexity algorithm, and it applies a local boosting to achieve a target intensity in backlight control. In performance evaluation using FPGA test system, the designed local dimming processor achieved 7.54% higher power‐saving rate with visual quality enhancement in high‐contrast region.

Human visual sensitivity based optimal local backlight dimming methodologies under different viewing conditions

An adaptive local backlight dimming algorithm is proposed considering human visual sensitivities under various viewing conditions. Local dimming amount is maximized based on contrast sensitivity function and local image characteristics to minimize perceived luminance and contrast losses maintaining image qualities. Average luminance, contrast and spatial frequency are evaluated as local image characteristics. As dimming based on local characteristics has blocking artifacts, a compensation method using edge luminance difference is proposed considering human responses. The proposed algorithms reduce backlight power consumption by 39.69% on average, with an average SSIM of 0.995. It can be increased by 5.66% with varying viewing conditions, resulting in a 45.35% power consumption reduction on average. The outperformances of the proposed algorithm in power consumption reduction and maintaining image quality are verified with various image quality metrics compared to recent dimming algorithms.

Using the Guided Fireworks Algorithm for Local Backlight Dimming

Local backlight dimming is a promising display technology, with good performance in improving the visual quality and reducing the power consumption of device displays. To set optimal backlight luminance, it is important to design high performance local dimming algorithms. In this paper, we focused on improving the quality of the displayed image, and take local backlight dimming as an optimization problem. In order to better evaluate the image quality, we used the structural similarity (SSIM) index as the image quality evaluation method, and built the model for the local dimming problem. To solve this optimization problem, we designed the local dimming algorithm based on the Fireworks Algorithm (FWA), which is a new evolutionary computation (EC) algorithm. To further improve the solution quality, we introduced a guiding strategy into the FWA and proposed an improved algorithm named the Guided Fireworks Algorithm (GFWA). Experimental results showed that the GFWA had a higher performance in local backlight dimming compared with the Look-Up Table (LUT) algorithm, the Improved Shuffled Frog Leaping Algorithm (ISFLA), and the FWA.

A rapid local backlight dimming method for interlaced scanning video

AbstractThis paper presents a rapid local backlight dimming method for interlaced video to improve the efficiency of displaying interlaced video. In the proposed method, we combine the line average deinterlacing algorithm with the local backlight dimming algorithm. In order to reduce the computational complexity and the backlight power consumption, three novel methods are proposed. The first is to add the sparse method to process the deinterlaced image. Second, the improved dynamic threshold method is used to calculate the dimming factor. And third, the odd field and even field of the same frame use the same backlight brightness to do backlight dimming. The simulation results show that the proposed method can reduce the computational complexity and power consumption, and the experiment results verify that the method can provide high display effect.

Optimal Local Dimming Based on an Improved Shuffled Frog Leaping Algorithm

The local backlight dimming technology has recently been presented for liquid crystal displays in order to reduce the power consumption of backlight and improve the quality of the display. Therefore, exploiting the tradeoff between the image quality and power consumption has become the focus of local backlight dimming technology. This paper considers the local backlight dimming as an optimization problem, i.e., how to preserve the image quality perception with a certain low backlight power consumption. To achieve this goal, we use the swarm intelligence algorithm. Specifically, an improved shuffled frog leaping algorithm is proposed for local backlight dimming. Simulation results show that the proposed algorithm achieves the better tradeoff between power consumption and image quality when compared to other algorithms based on image parameters.

Modeling the Quality of Videos Displayed With Local Dimming Backlight at Different Peak White and Ambient Light Levels.

This paper investigates the impact of ambient light and peak white (maximum brightness of a display) on the perceived quality of videos displayed using local backlight dimming. Two subjective tests providing quality evaluations are presented and analyzed. The analyses of variance show significant interactions of the factors peak white and ambient light with the perceived quality. Therefore, we proceed to predict the subjective quality grades with objective measures. The rendering of the frames on liquid crystal displays with light emitting diodes backlight at various ambient light and peak white levels is computed using a model of the display. Widely used objective quality metrics are applied based on the rendering models of the videos to predict the subjective evaluations. As these predictions are not satisfying, three machine learning methods are applied: partial least square regression, elastic net, and support vector regression. The elastic net method obtains the best prediction accuracy with a spearman rank order correlation coefficient of 0.71, and two features are identified as having a major influence on the visual quality.

Viewing Distance-Based Perceived Error Control for Local Backlight Dimming

This paper presents an effective local dimming algorithm that preserves the perceived image quality consistently in the backlight dimmed images regardless of viewing distances. The proposed algorithm determines the clipped points of each LED block by limiting the maximum size of image area to be distorted, and guarantying the minimum image quality in terms of the peak signal-to-noise ratio. It also preserves the perceived image quality of the dimmed images by adjusting the size of area to be distorted depending on the viewing distances of users. Simulation results show that the proposed method improves the average PSNR and the average SSIM values of the dimmed images by 4.19–13.21 dB and 0.002–0.004, compared with the benchmark methods, for viewing distances of 2.5–6.5 m, respectively. The proposed method also maintains the image quality of the dimmed images regardless of the image's characteristics, compared with the benchmark methods. In addition, it is confirmed that the proposed method achieves the higher power savings as the viewing distance increases. At the viewing distance of 6.5 m, although the image quality of the dimmed images are higher than that of the benchmark methods, the proposed method consumes 0.56% less power.

A Novel Partitioned Light Guide Backlight LCD for Mobile Devices and Local Dimming Method With Nonuniform Backlight Compensation

Conventional backlight dimming methods can hardly be used in edge type backlight LCD. In order to perform a power efficient backlight local dimming in LCD of mobile devices, a novel backlight module structure called partitioned light guide (PLG) was proposed. The PLG backlight module consists of independently controlled light sources, allowing the light luminance distribution to be controlled locally and efficiently. A PLG LCD prototype with white LEDs was built for evaluation. It was proved that local backlight dimming can be performed effectively in the edge type LCD. In addition, to compensate the backlight nonniformity which was caused by light leakage at the boundaries of PLG, an image distortion driven local dimming algorithm was proposed. Image distortion level of displayed image was selected by the user to determine how much compromise was made between power saving ratio and image quality. More simulations with RGB LED light sources showed the method can significantly improve the power efficiency of edge type backlight LCD, compared with global dimming method and SSC method.

Local Luminance Boosting of an RGBW LCD

Compared to a conventional RGB LCD, an RGBW LCD is known to result in 50% higher light transmission. However, the reduced aperture for the RGB subpixels lead to reduced luminance for saturated pixels. Consequently, colorful images may appear dull due to a lack of sufficient luminance. In this work it is proposed to address the luminance shortage for bright saturated pixels by boosting a spatially modulated backlight. Whereas best-in-class methods for deriving backlight drive levels either results in high contrast or temporal stability, we propose a reformulation which provide superior contrast and temporal stability. By employing local backlight boosting, the 99.5% percentile of ΔE94 is reduced from 12.3 JND to 4.3 JND on average. Power consumption is reduced by 18% compared to an RGB LCD with local backlight dimming. Additionally, we propose to increase luminance of desaturated pixels in regions of backlight boosting, which results in an average luminance increase of 16% for pixels which are boosted.

Block-Based Gradient Descent for Local Backlight Dimming and Flicker Reduction

Local backlight dimming technology is a two-fold improvement for LED backlit LCD screens that allows to reduce power consumption and increase visual quality. This paper presents a fast version of an iterative backlight dimming algorithm based on gradient descent search. The speed is increased by exploiting the local uniformity of backlight to reduce the complexity for determining the optimal backlight of a given image. The algorithm is adapted to video sequences by using the backlight of the previous frame as a starting point to calculate the backlight for the current frame. Fast variations of backlight dimming over time can produce a visually annoying flicker artifact. To avoid this artifact, a control mechanism is also proposed.

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)

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.