一种基于LCD-LED双调制显示器的HDR图像显示方法

提出一种针对HDR图像的显示方法,该方法应用于LCD-LED双调制高动态显示器,旨在使显示器更好地显示HDR图像要求的亮度细节,提高视觉质量。首先,建立HDR图像亮度与LED亮度范围对应关系,使用光扩散函数作为背光LED亮度取值范围的权重。然后,统计LED的亮度辐射区域内不同LED发光强度等级的权重,取权重最大者对应的亮度作为该背光LED亮度。最后,利用依据LED亮度生成LED背光扩散图像与HDR图像计算出LCD显示图像。仿真结果表明,该算法可以使显示器亮度失真率系数低至0.006以下。在LCD-LED双调制高动态显示器上实验验证结果表明,该算法可以有效提高图像的层次感,有效抑制LCD-LED双调制高动态显示器的"光晕"以及亮度截断现象,提高显示质量。     

关于点阵式LED动态背光源及其驱动电路的设计

由于液晶本身不发光,需要通过背光照明,因此目前大多数产品采用冷阴极射线荧光灯（CCFL）作为背光源,但因CCFL的亮度不容易控制和响应速度慢等缺点,造成液晶显示的能源浪费和动态模糊。文章提出了一种基于点阵式LED的动态背光源结构,将单个LED发出的光投射区域限制在散光膜的单一区域,即每个LED只负责液晶部分区域的背光照明。文章还设计了动态背光源的驱动电路,通过对显示的画面进行分析．采用亮度动态控制的方式可以得到不同区域的最佳亮度,同时驱动LED背光达到相应的亮度。并利用Matlab软件仿真LED背光源,结果表明采用动态背光源能有效地降低功耗．提高图像对比度。     

Tone mapping with contrast preservation and lightness correction in high dynamic range imaging

In real-world environments, the human visual system perceives a wide range of luminance in a scene. However, the full range of tones in a high dynamic range (HDR) scene cannot be displayed on standard display devices due to their low dynamic range (LDR). Therefore, tone mapping is necessary to faithfully display a HDR scene on an LDR display device. Existing tone mapping methods have problems because details and contrast in a scene are not preserved faithfully, and they also distort the colors in a scene. Thus, we propose a tone mapping method for preserving the detail in an HDR scene using a weighted least squares filter, which preserves the global contrast in a scene by using a competitive learning neural network, before applying a tone reproduction operator to preserve the color without shifting the lightness. According to the Helmholtz–Kohlrausch effect, the perception of brightness depends on the lightness, chroma, and hue of a color. For example, the luminance of pixels with specific colors such as red and blue is low in an HDR scene. The proposed method corrects the lightness of pixels according to the color (i.e., lightness, chroma, and hue) of a tone-mapped image. Experimental results with several test sets of images demonstrated that the proposed tone mapping method with contrast preservation and lightness correction is more suitable for dynamic range compression than existing tone mapping methods, while it also preserves the color of a scene in an effective way.     

Mixed Color Sequential Technique for Reducing Color Breakup and Motion Blur Effects

This paper proposes a mixed color sequential (MCS) algorithm with high contrast enhancement technique in RGB light-emitting diode (LED) backlight display. Owing to synchronous control of liquid crystal display (LCD) and LED panels, high quality image with suppressed color breakup (CBU) and motion blur effects is achieved by our novel color sequential technique. Importantly, MCS algorithm is useful for color filter-less optical compensated bend (OCB) panel display for alleviating CBU and motion blur effects. Furthermore, high contrast image is also presented on LCD panel because of mixed red-green-blue (RGB) and cyan-magenta-yellow (CMY) backlights with optimum power consumption. In other words, MCS algorithm with high contrast enhancement technique can have the better performance compared with other field sequential color techniques. Experimental results demonstrate by an actual RGB backlight module for 32-in 1366*768 LCD panel the improvement of CBU and motion blur effects.     

Design and Evaluation of Light Spread Function for Area-Adaptive LCD System

A methodology, based on two-dimensional super-Gaussian light spread functions (LSFs), was studied for the light-emitting-diode (LED) backlighting system in the high dynamic range (HDR) liquid crystal displays (LCDs). We proposed a novel LED-based optomechanical configuration to implement the desirable luminous pattern. A dual-liquid-crystal-panel system was constructed as a pseudo-HDR LCD to evaluate the super-Gaussian illumination. The proposed HDR scheme was verified via the current platform: overall luminance uniformity, contrast ratio and processing speed could be improved by factors of 1.55, 1.95–4.15, and 4.82, respectively. The design flexibility made the methodology applicable to any panel dimension and backlight division of the HDR LCDs, and to the conventional full-on backlighting LCDs as well.      

Real-Time Tone-Mapping Processor with Integrated Photographic and Gradient Compression using 0.13 μm Technology on an Arm Soc Platform

Due to recent advances in high dynamic range (HDR) technologies, the ability to display HDR images or videos on conventional LCD devices has become more and more important. Many tone-mapping algorithms have been proposed to meet this end, the choice of which depends on display characteristics such as luminance range, contrast ratio and gamma correction. An ideal HDR tone-mapping processor should have a robust core functionality, high flexibility, and low area consumption, and therefore an ARM-core-based system-on-chip (SOC) platform with a HDR tone-mapping application-specific integrated circuit (ASIC) is suitable for such applications. In this paper, we present a systematic methodology for the development of a tone-mapping processor of optimized architecture using an ARM SOC platform, and illustrate the use of this novel HDR tone-mapping processor for both photographic and gradient compression. Optimization is achieved through four major steps: common module extraction, computation power enhancement, hardware/software partition, and cost function analysis. Based on the proposed scheme, we present an integrated photographic and gradient tone-mapping processor that can be configured for different applications. This newly-developed processor can process 1,024 × 768 images at 60 fps, runs at 100 MHz clock and consumes a core area of 8.1 mm² under TSMC 0.13 μm technology, resulting in a 50% improvement in speed and area as compared with previously-described processors.     

基于灰阶熵的LCD动态背光调整

飞机中液晶显示屏上显示的一般是图形和数据,显示界面上有较大范围是暗场景。若采用传统液晶显示器恒定亮度的面光源,会造成不必要的电能消耗,且存在漏光现象导致图像的对比度下降,因此对液晶显示的背光源采用动态背光的控制。文章通过分析常见的平均值和最大值背光亮度提取方法,提出基于灰阶熵的LCD背光亮度调整方法。该方法既解决平均值法失真严重的问题,保证图像质量,同时相比于最大值法又减少功耗,达到降低功耗和保证图像质量的要求。     

Reduction of power consumption in compact DFD display by using FS color technology

A method to drastically reduce the power consumption of the backlight in a compact depth-fused three-dimensional display, which consists of a stack of two liquid crystal (LC) panels, is proposed and experimentally validated. To remove the color filters in the LC panels, we introduced the field-sequential technique for color display. The transmittance of the display could be improved by more than one order. Therefore, the luminance of the backlight could be reduced to less than that of a two-dimensional LC display.     

基于颜色空间转换的高动态图像双屏显示方法

针对高动态范围图像映射后偏色问题及图像细节显示不足问题,提出了一种基于颜色空间转换与双屏结合的显示方法。首先将高动态图像转换到HSL空间,采用自适应对数算法进行亮度映射及相应的饱和度增强,再次转换到RGB空间并进行LCD-FED双屏分割显示。实验结果表明该方法不仅解决了偏色问题,而且在细节表现能力上也有了很大的提升,其失真度仅为3.7%。     

Minimum-Error Splitting Algorithm for a Dual Layer LCD Display—Part II: Implementation and Results

A dual layer liquid crystal display (LCD) is able to achieve a high dynamic range by stacking two liquid crystal panels one on top of the other over an enhanced backlight unit. However, the finite distance between the two panels inevitably introduces a parallax error when the display is observed off-axis, and the dynamic range limitations of the individual panels introduce a reconstruction error near sharp edges in the input image. In Part I, we have formulated the image splitting as a constrained optimization problem in which a joint minimization of the parallax error and the visibility of the reconstruction error is performed.      

HDR技术与区域调光算法

高动态范围图像是当前全球显示及电视行业最热门的先进技术,它可以提供更多的动态范围和图像细节。创维研发的高动态范围、高亮度、高对比度的背光控制技术,实现了LED动态多分区光源处理,可以提供更广、更精准、影像动态范围更高的画面处理能力。本文主要介绍了HDR技术和区域调光背光驱动与算法研究。     

基于双边滤波的多尺度分层色调映射算法

为增强高动态范围图像(High dynamic range,HDR)的显示效果,本文提出一种多尺度梯度域色调映射算法。首先提取高动态范围图像的亮度信息,利用双边滤波将高动态范围图像的亮度数据进行多尺度分解,得到基本层和细节层。由于视觉上的亮度变化体现为图像数据的梯度变化,因此可在梯度域对基本层图像进行自适应动态范围压缩,然后加上细节层图像信息,最后再通过色彩校正算法恢复图像色彩,实现HDR图像的动态范围压缩。通过对比算法的定量分析表明,本文算法的方差和信息熵的客观指标分别提高了30.8%和5.9%,因此,本文方法在压缩HDR图像的动态范围的同时,可以更好地保留边界、纹理等细节信息。     

基于U型导光板的特种液晶显示背光模组设计

提出一种基于U型导光板的特种液晶显示背光模组以缩小侧入式背光模组的厚度。首先,利用Lighttools软件对分别采用1 mm和2 mm U型导光板的曲型侧边背光模组进行了设计和建模;接着对两种不同厚度的曲型侧边背光模组与采用4 mm常规平板式导光板的侧入式背光模组进行仿真并对比分析;最后对采用2 mm U型导光板的曲型侧边背光模组进行了相对偏移的仿真,结果表明其光学性能在强振动和宽温环境中具有较高的稳定性。文章得到一种采用2 mm U型导光板的曲型侧边背光模组,相比较常规侧入式背光模组,在保持了光学性能一致性的前提下厚度缩小了2 mm,对特种显示器的薄型化设计有一定的参考意义。     

高动态范围LCD显示中区域控制型LED背光驱动信号的导出

LED背光技术不仅显著增强了LCD显示的动态范围,同时使现有图像达到了更逼真的显示效果。通过对LED单独控制,可为显示提供区域可控的LED背光。然而,LED之间的干扰在这里不仅仅为我们提供了较高的亮度,同时也是产生潜在虚假图像的原因,这使得导出最佳LED驱动信号成为一项具有挑战性的工作。本文通过两个数学模型:迭代解旋法和线性优化法,计算分析了上述问题。并给出了这两个数学模型的算法,同时建立了一个包含161个高动态范围图像的图像数据库,对上述两种方法的效果进行了评估。     

时空混合控制式自由立体显示系统背光刷新方式优化研究

时空混合控制式自由立体显示是一种新型的自由立体显示技术,具有全分辨率和低串扰率优点,消除了背光源刷新与屏幕图像刷新不同步所导致的时域串扰率升高,这是时空混合控制式自由立体显示的关键问题之一。本文介绍了时空式立体显示系统的原理和动态背光的工作方式,提出了扫描式和垂直式两种不同的背光源刷新方式,着重对比了两种背光源刷新方式对屏幕亮度和串扰率的影响。通过实验测量给出了时空式自由立体显示系统背光源刷新的最优化参数设置。在优化配置条件下,系统串扰率低至2.64%,证明动态背光同步技术可以有效降低系统的时域串扰率。     

基于调制传递函数(MTF)的LCDs运动模糊研究

当运动图像在以LCDs为典型代表的保持型显示器上显示时,会产生诸如运动模糊之类的伪像这种图象质量的下降可以解释为LCDs显示运动图像时表现出的MIF低通特性.本文介绍了调制传递函数理论及其在像质评价中的应用方法,并运用调制传递函数理论从频域的角度分析了LCDs运动图像的显示特性、LC响应时间对运动模糊的影响以及背光闪烁的方法改善运动模糊的效果.     

Methods for improving the tone mapping for backward compatible high dynamic range image and video coding

Backward compatibility for high dynamic range image and video compression forms one of the essential requirements in the transition phase from low dynamic range (LDR) displays to high dynamic range (HDR) displays. In a recent work [1], the problems of tone mapping and HDR video coding are originally fused together in the same mathematical framework, and an optimized solution for tone mapping is achieved in terms of the mean square error (MSE) of the logarithm of luminance values. In this paper, we improve this pioneer study in three aspects by considering its three shortcomings. First, the proposed method [1] works over the logarithms of luminance values which are not uniform with respect to Human Visual System (HVS) sensitivity. We propose to use the perceptually uniform luminance values as an alternative for the optimization of tone mapping curve. Second, the proposed method [1] does not take the quality of the resulting tone mapped images into account during the formulation in contrary to the main goal of tone mapping research. We include the LDR image quality as a constraint to the optimization problem and develop a generic methodology to compromise the trade-off between HDR and LDR image qualities for coding. Third, the proposed method [1] simply applies a low-pass filter to the generated tone curves for video frames to avoid flickering during the adaptation of the method to the video. We instead include an HVS based flickering constraint to the optimization and derive a methodology to compromise the trade-off between the rate-distortion performance and flickering distortion. The superiority of the proposed methodologies is verified with experiments on HDR images and video sequences.     

大动态宽幅度自由立体显示背光控制系统

提出并实现一种大动态宽幅度自由立体显示背光控制系统。本系统采用LCD作为基本显示屏幕,以柱镜光栅作为指向性光学部件,以LED阵列作为可寻址背光组件,以步进电机改变栅屏距离,采用Atmega128单片机作为控制处理器,辅以高精度实时人眼跟踪模块与之通信。本系统的大动态体现在观看视角较大且连续,宽幅度体现在可同时满足多个有效观看距离。     

液晶电视LED背光模组及区域调光控制技术浅析

随着LCD产业成本的不断降低,液晶电视作为一种新型的显示设备已在逐步取代传统的CRT屏而成为市场的主流。作为液晶显示设备的主体器件,背光模组技术的发展已经成为液晶显示设备发展的重要指标而被各大厂商所重视,从技术发展趋势上来说,如何降低背光的功耗最受到关注。     

Noise reduction in high dynamic range images

Multiple images with different exposures are used to produce a high dynamic range (HDR) image. Sometimes high-sensitivity setting is needed for capturing images in low light condition as in an indoor room. However, current digital cameras do not produce a high-quality HDR image when noise occurs in low light condition or high-sensitivity setting. In this paper, we propose a noise reduction method in generating HDR images using a set of low dynamic range (LDR) images with different exposures, where ghost artifacts are effectively removed by image registration and local motion information. In high-sensitivity setting, motion information is used in generating a HDR image. We analyze the characteristics of the proposed method and compare the performance of the proposed and existing HDR image generation methods, in which Reinhard et al.’s global tone mapping method is used for displaying the final HDR images. Experiments with several sets of test LDR images with different exposures show that the proposed method gives better performance than existing methods in terms of visual quality and computation time.