Performance analysis of a backlight dimming method using weighted mean-square-error based on joint edge-saliency characteristics

In this paper, a new backlight dimming method using weighted mean-square-error (MSE) based on joint edge-saliency characteristics is proposed. In contrast to conventional backlight dimming methods that cannot accurately evaluate the saturation error and determine the optimal clipping point to achieve the best trade-off between image quality and power consumption, the proposed method, with consideration of human visual characteristics, analyzes the joint edge-saliency characteristics based on spatio-temporal saliency map and edge-strength map of the input images, and weights the MSE accordingly. It can therefore evaluate the allowable saturation error and determine the optimal clipping point. Simulation results show that the proposed method outperforms other benchmark methods in the case of overall consideration of image quality and power consumption. Additionally, the proposed method maximizes the power reduction rate while successfully preserving image details in the regions of interest and maintaining high perceived image quality. Our results also show that the average computation time of the proposed algorithm was reduced by up to 30.184%, 19.162% and 8.027%, respectively, compared with I²GEC, SMVA² and SPBD algorithms.     

High‐performance local‐dimming algorithm based on image characteristic and logarithmic function

With the emergence of high‐dynamic range (HDR) image and video, displaying an HDR image or video on a standard dynamic range displays with natural visual effect, clear details on local areas, and high‐contrast ratio has become an important issue. To achieve HDR, local‐dimming technique has been commonly practiced. In this paper, we investigate the problem of local dimming for LED‐backlight LC display to provide algorithm support for developing HDR displays. A novel local‐dimming algorithm is proposed to improve the contrast ratio, enhance the visual quality, and reduce the power consumption of the LCDs. The proposed algorithm mainly consists of two parts. The first part is a backlight luminance extraction method based on dynamic threshold and the maximum grayscale of an image block to improve the contrast ratio and reduce the power consumption. In the second one, a pixel compensation method based on logarithmic function is used to improve the visual quality and contrast ratio. At the same time, in order to better smooth the backlight diffusion at the edges of the backlight luminance signal to enhance the accuracy of the pixel compensation, we draw on the idea of BMA and improve it to establish the backlight diffusion model with different low‐pass‐filter templates for different types of blocks. Simulation and measured results show that the proposed algorithm outperforms the competing ones in contrast ratio, visual quality, and power‐saving ratio.     

IPS‐mode dynamic LCD‐TV realization with low black luminance and high contrast by adaptive dynamic image control technology

Abstract— In this paper, an active backlight control technology and a data‐processing algorithm has been developed to improve the image quality in IPS‐mode LCD TVs. The image‐blinking problem caused by repeatedly abrupt changes in the backlight luminance was solved by using algorithms [Fba (flexible‐boundary algorithm) and Cfa (cumulative feedback algorithm)] and an optimized number of backlight dimming steps based on human perception. In the IPS‐mode 42‐in. TFT‐LCD panel, the dynamic contrast ratio can be more than twice the typical level by means of a lower black luminance and a higher white luminance. Additionally, the power consumption and LCD temperature were lowered.     

Backlight dimming based on saliency map acquired by visual attention analysis

Displays have been used in various applications from mobile phones to tablets, and the low power consumption is one of their most important factors. Backlight dimming is the most promising technique to achieve this because it significantly reduces the display power by controlling only the transmittance of liquid crystal. This paper proposes a new backlight dimming algorithm using visual attention analysis. Conventional algorithms have a serious saturation error in some images when performing backlight dimming, thereby degrading image quality. In contrast, the proposed algorithm analyzes image characteristics based on the saliency map, which considers human visual attention. It then truncates the meaningless information of the saliency map using an adaptive saliency level selection approach and calculates the maximum amount of saturation error that humans will not perceive. In addition, the proposed algorithm defines the objective function and computes the optimal starting gray level in that function to calculate the saturation error. Simulation results show that the proposed algorithm using the adaptive saliency level selection approach performs best. In addition, the average peak signal-to-noise ratio of the proposed algorithm was up to 3.762 dB higher than that of the conventional algorithm while slightly increasing the power consumption.     

How to reduce light leakage and clipping in local‐dimming liquid‐crystal displays

Abstract— In conventional LCDs, the backlight is set to maximum luminance regardless of the image. For dark scenes, this approach causes light leakage and power waste. Especially, light leakage in dark scenes degrades the contrast ratio of LCDs; to circumvent this problem, local‐dimming systems have been proposed. In these systems, the LED backlight is divided into several local blocks and the backlight luminance of each local block is controlled individually, and pixel values are adjusted simultaneously according to the luminance profile of the dimmed backlight. In this paper, a method of determining the LED backlight luminance of each local block depending on the image is proposed; this method significantly improves the image quality of LCDs. First, we introduce methods of quantifying light‐leakage at dark gray levels and clipping at bright gray levels. Then, the proposed method to determine the dimming duty, which controls the LED backlight luminance by compromising between these two measures, was derived. The proposed algorithm preserves the original image with little clipping distortion and effectively reduces light leakage.     

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.     

White‐LED backlight control for motion‐blur reduction and power minimization in large LCD TVs

Abstract— A 1‐D LED‐backlight‐scanning technique and a 2‐D local‐dimming technique for large LCD TVs are presented. These techniques not only reduce the motion‐blur artifacts by means of impulse representation of images in video, but also increase the static contrast ratio by means of local dimming in the image(s). Both techniques exploit a unique feature of an LED backlight in large LCD TVs in which the whole panel is divided into a pre‐defined number of regions such that the luminance in each region is independently controllable. The proposed techniques are implemented in a Xilinx FPGA and demonstrated on a Samsung 40‐in. LCD TV. Measurement results show that the proposed techniques significantly reduce the motion‐blur artifacts, enhance the static contrast ratio by about 3×, and reduce the power consumption by 10% on average.     

A rapid local backlight dimming method for interlaced scanning video

This 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.     

Local dimming light‐guiding plate type backlight system using alignment‐controlled polymer‐dispersed liquid crystals

A new technology which enables a local brightness control according to the displayed images has been expected in the thin and lightweight backlight systems to improve a contrast ratio and power consumption of the liquid crystal displays (LCDs). In this paper, we have proposed a novel local‐dimming backlight system using alignment‐controlled polymer‐dispersed liquid crystals as a light‐guiding plate and investigated the forming conditions of polymer‐dispersed liquid crystals to achieve both a high‐luminance ratio and a fast response speed. As a result, we found that a luminance ratio and response speed of the backlight system can be improved by using bifunctional LC monomer materials and forming fine and rigid polymer network in the LCs, and achieved high luminance ratio of 16:1 and fast response time less than 0.5 ms. In addition, we fabricated the twisted nematic‐mode LCD using the local dimming light‐guiding plate‐type backlight based on this design, and successfully realized eight times higher contrast ratio than that of the traditional twisted nematic‐mode LCD.     

Performance analysis of structural similarity-based backlight dimming algorithm modulated by controlling allowable local distortion of output image

This paper proposes a global backlight dimming algorithm based on structural similarity that controls the local distortion level of the output image for preserving overall image quality. Unlike existing methods, the proposed method non-iteratively determines a global clipping point that maintains structural similarity for each pixel above the desired level. The proposed method consists of three steps: region analysis, candidate clipping point calculation, and backlight luminance determination. In the first step, the structural similarity is analyzed based on various clipping points. In the second step, the proposed method estimates a candidate clipping point, which preserves the structural similarity index of each pixel above the desired level, based on the estimation of local statistics. Then, the proposed method determines a global clipping point based on a group of candidate clipping points. Finally, the output luminance is determined based on the selected global clipping point. Experimental results showed that the proposed method successfully maintained the structural similarity of each pixel above the desired level. In addition, the proposed method reduced the variation of minimum structural similarity by up to 94.7% compared to the benchmark methods.     

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.     

Color‐breakup suppression and low‐power consumption by using the Stencil‐FSC method in field‐sequential LCDs

Abstract— Field‐sequential color (FSC) is a potential technique for low‐power liquid‐crystal displays (LCDs). However, it still experiences a serious visual artifact, color break‐up (CBU), which degrades image quality. Consequently, the “Stencil Field‐Sequential‐Color (Stencil‐FSC)” method, which applies local color‐backlight‐dimming technology at a 240‐Hz field rate to FSC‐LCDs, is proposed. Using the Stencil‐FSC method not only suppressed CBU efficiently but also enhanced the image contrast ratio by using low average power consumption. After backlight signal optimization, the Stencil‐FSC method was demonstrated on a 32‐in. FSC‐LCD and effectively suppressed the CBU, which resulted in more than a 27,000:1 dynamic contrast ratio and less than 40‐W average power consumption.     

High power-saving and fidelity-conserving object-based local dimming for LCD systems with LED-based backlight units

A local dimming technique which is enabled on LED-based LCD systems is expected to give more power saving than a global one. However, prior local dimming techniques have not considered human visual system-awareness much as done in an advanced global dimming technique. In this paper, we propose a novel local dimming technique using an object-based approach for both good human visuality and high power saving. It utilizes prevalent colors of individual objects in a given image to do initial dimming, and then enhances the image using a proper fidelity threshold to reduce visible artifacts. Experimental results show that the proposed technique achieves power saving up to 13 and 12 times higher than human visual system-aware global dimming and prior well-designed local dimming techniques, respectively, with a similar human visual system-aware image quality level in a uniform backlight optical profile. It achieves power saving up to 15 and 6 times higher in a Gaussian-based backlight optical profile. Due to a good use of a simpler image fidelity metric, the proposed technique also can make the complexity go lower while keeping a satisfactory image quality.

     

Human visual perception‐based localized backlight scaling method for high dynamic range LCDs

This paper presents a backlight control algorithm for liquid crystal display devices, which considers the human visual properties that we are usually attracted to the saliencies in a scene. The saliency means regions or objects that have different contrast or color from the surrounding, and thus attract our attention, which can be measured in various ways from each pixel value and its relation with the surrounding ones. Hence, by keeping or boosting the backlight of salient regions while suppressing in others, the quality of salient regions and overall contrast are enhanced. In addition, power can be saved by backlight dimming in non‐salient regions, without loss of overall quality in terms of human visual perception. In this backlight control process, the amount of energy consumption is regulated so that the proposed method consumes less than or equal energy as before, by developing a power management algorithm based on the bit rate control strategies of MPEG2 video encoders. Precisely, the energy consumption in each backlight unit is controlled by a parameter, so that the sum of energies of overall backlight units is kept within a limit.     

Characterizing image quality of autostereoscopic displays by using the maximum luminance at each viewing position

A metric of the 3D image quality of autostereoscopic displays based on optical measurements is proposed. This metric uses each view's luminance contrast, which is defined as the ratio of maximum luminance at each viewing position to total luminance at that position. Conventional metrics of the autostereoscopic display based on crosstalk, which uses “wanted” and “unwanted” lights. However, in case of the multiple‐views‐type autostereoscopic displays, it is difficult to distinguish exactly which lights are wanted lights and which are unwanted lights. This paper assumes that the wanted light has a maximum luminance at the good stereoscopic viewing position, and the unwanted light also has a maximum luminance at the worst pseudo‐stereoscopic viewing position. By using the maximum luminance that is indexed by view number of the autostereoscopic display, the proposed method enables characterizing stereoscopic viewing conditions without using wanted/unwanted light. A 3D image quality metric called “stereo luminance contrast,” the average of both eyes' contrast, is proposed. The effectiveness of the proposed metric is confirmed by the results of optical measurement analyses of different types of autostereoscopic displays, such as the two‐view, scan‐backlight, multi‐view, and integral.     

Contrast gain and power savings using local dimming backlights

Abstract— The contrast and power consumption of today's liquid‐crystal displays (LCDs) can be improved substantially by introducing (local) dimming backlights. In fact, infinite dynamic contrast and power savings of well over 50% have been claimed for such displays. Because these claims are generally made for very specific backlight designs and image content, the contrast gain and power savings are quantified as a function of the number of backlight segments for a large variety of image content.     

Adaptive height-modified histogram equalization and chroma correction in YCbCr color space for fast backlight image compensation

Automatic exposure controls in commercially available cameras often encounter difficulties in capturing scenes with backlight luminance which dominates the entire image. An Adaptive Height-Modified Histogram Equalization (AHMHE) algorithm is proposed as a compensation technique for backlight images. It simultaneously enhances contrast in both the dark and the bright areas without creating regions of degraded local contrast. Moreover AHMHE is an adaptive algorithm: thus it requires minimal user input, and its reduced computational requirement makes it suitable for real-time application. In addition to AHMHE, a chroma correction technique was applied to chroma components in the YCbCr color space to produce more vivid color images. A series of subjective and index evaluations were conducted to measure the resultant image quality improvements by the AHMHE and the chroma correction algorithms.     

Luminance adaptation transform based on brightness functions for LDR image reproduction

Tone mapping algorithms are used for image processing to reduce the dynamic range of an image to be displayed on low dynamic range (LDR) devices. The Retinex, which was developed using multi-scale and luminance-based methods, is one of the tone mapping algorithms for dynamic range compression, color constancy and color rendition. Retinex algorithms still have drawbacks, such as lower contrast and desaturation. This paper proposes a multi-scale luminance adaptation transform (MLAT) based on visual brightness functions for the enhancement of contrast and saturation of rendered images. In addition, the proposed algorithm was used to estimate the minimum and maximum luminance and a visual gamma function for local adapted viewing conditions. MLAT showed enhanced contrast and better color representation than the conventional methods in the objective evaluations (CIEDE200 and VCM).     

Efficacy of global dimming backlight and high‐contrast liquid crystal panel for high‐dynamic‐range displays

Using an RGB organic light‐emitting diode display to emulate liquid crystal display systems, we examined the efficacy of different global dimming strategies for cinematic content. A global dimming solution with smoothed transitions was preferred over solutions using a static backlight level or the highly aggressive frame‐by‐frame backlight adjustment scheme. We compared two such smoothing approaches, one making use of causal data, and another using future information (which could be available via latency or dynamic metadata) and did observe some opportunities for an improved experience, but found the causal data to be a competitive approach. We also evaluated the importance of native panel contrast and how global dimming compares to local dimming approaches. For most content tested, a global dimming display with a high‐contrast liquid crystal panel was judged as being equivalent or more preferred to a full‐array local dimming display with a low‐contrast panel. These results build on the existing evidence that native panel contrast remains one of the strongest predictors of high‐dynamic‐range image quality even as backlight technologies continue to improve.