Scanning backlight for motion‐blur reduction on mobile displays

Abstract— Small‐form‐factor liquid‐crystal displays (LCDs) are mainly used in mobile applications (e.g., mobile phones, PDAs, and portable game consoles) but also in digital still cameras, video cameras, automotive applications, etc. Like all active‐matrix LCDs, mobile displays suffer from motion blur caused by the sample‐and‐hold effect. One option for improving the motion portrayal on active‐matrix LCDs is the use of a scanning backlight, which results in an imaging behavior similar to the one present in impulsive displays. In this paper, the realization of a scanning backlight for mobile displays is reported. This employs a backlight with seven individually lit segments for reducing the motion blur. Results of perception experiments performed with two identical displays confirm the benefit of using this technology. Optimal driving conditions result in a major improvement in motion portrayal on mobile LCDs.     

Evaluation of motion performance on scanning‐backlight LCDs

Abstract— The scanning‐backlight technique to improve the motion performance of LCDs is introduced. This technique, however, has some drawbacks such as double edges and color aberration, which may become visible in moving patterns. A method combining accurate measurements of temporal luminance transitions with the simulation of human‐eye tracking and spatiotemporal integration is used to model the motion‐induced profile of an edge moving on a scanning‐backlight LCD‐TV panel that exhibits the two drawbacks mentioned above. The model results are validated with a perception experiment including different refresh rates, and a high correspondence is found between the simulated apparent edge and the one that is perceived during actual motion. Apart from the motion‐induced edge blur, the perception of a moving line or square‐wave grating can also be predicted by the same method starting from the temporal impulse and frame‐sequential response curves, respectively. Motion‐induced image degradation is evaluated for both a scanning‐ and continuous‐backlight mode based on three different characteristics: edge blur, line spreading, and modulation depth of square‐wave grating. The results indicate that the scanning‐backlight mode results in better motion performance.     

Moving‐image simulation for high‐quality LCD TVs

Abstract— A simulation system incorporating pixel response and eye‐trace integration was developed to evaluate the moving‐image performance of high‐quality LCD TVs. A simple formula was derived for moving‐edge simulation, which can be used to evaluate the visual effects of arbitrary response waveforms. A model of exponential decay with dynamic time constants is proposed for the LC response to perform moving‐image simulation. The model was used to evaluate the visual effects of various motion‐blur‐reduction techniques. Six different motion‐blur‐reduction techniques were evaluated in terms of their visual effects. Among them, three basic techniques show certain defects, which are further analyzed by simulation. The other three advanced techniques show excellent performance, and, therefore, are recommended for use in high‐quality LCD TVs.     

Characterizing displays by their temporal aperture: A theoretical framework

Abstract— The spatio‐temporal aperture and sample rate of a video display determines both the static and dynamic resolution of the video signal that is rendered. The dynamic display characteristics like the visibility of large‐area flicker, motion judder, and motion blur can be derived from the frame rate and the temporal extent of the pixel aperture (i.e., the temporal aperture). For example, liquid‐crystal displays (LCDs) have an aperture that is relatively small in the spatial dimension and wide in the temporal domain. Consequently, moving objects displayed on an LCD suffer from motion blur. Especially in TV applications, the temporal dimension has a large impact on the overall picture quality. The temporal aperture, together with the frame rate, is shown to predict the amount of perceived large‐area flicker, motion judder, and motion blur and also the performance of motion‐blur reduction algorithms for LCDs. From this analysis it is further determined how to obtain the optimal temporal aperture of a television display, for which not only properties of the human visual system (HVS), but also the properties of the video signal have to be taken into account.     

Analysis of response‐time compensation for black‐frame insertion

Abstract— An impulsive driving technique has been widely adopted for the elimination of motion blur in LCDs. Although the problem of slow temporal response time is very well known for LCDs, the inherent motion blur of moving objects in hold‐type displays has a more‐serious impact on display performance. It is well known that even very fast LCDs with zero response time still suffer from the motion‐blur artifact due to hold‐type driving effects. However, a fast temporal response is also critical in order to maximize the blur‐reduction effect even in the case of impulsive driving. In this paper, the special behavior of LC molecules in an impulsive driving environment has been analyzed especially for the case of black‐frame insertion, and we propose an effective means to implement optimized response‐time compensation (RTC) for the black‐frame insertion technique.     

Motion‐blur characterization on liquid‐crystal displays

Abstract— In this paper, several methods to characterize motion blur on liquid‐crystal displays are reviewed. Based on the assumptions of smooth‐pursuit eye tracking and one‐frame temporal luminance integration, a simple algorithm has been proposed to calculate the normalized blurred edge width (N‐BEW) and motion‐picture response time (MPRT) with a one‐frame‐time moving‐window function to LC temporal step response curves. A custom measurement system with a fast‐eye‐sensitivity‐compensated photodiode has been developed to characterize motion blur based on LC response curves (LCRCs). MPRT values obtained by using the algorithm mentioned above and those from the smooth‐pursuit‐camera methods agree. Perception experiments were conducted to validate the correspondence between the simulated results and actual perceived images by the human eyes. In addition, the insufficiency of MPRT to evaluate motion blur on impulse‐type light‐generation LCDs, by analyzing the measurement results of a scanning backlight LCD, is discussed.     

Next‐generation mobile LCDs with in‐cell retarders

Abstract— In‐cell retarders can be a major breakthrough for mobile LCDs. When a patterned in‐cell retarder replaces the external retarders on transflective LCDs, brighter and thinner transflective LCDs with lower power consumption and wider viewing angle can be obtained. Additionally, when in‐cell retarders are applied in reflective LCDs, the thickness of the LCD is considerably reduced without affecting the optical performance of the reflective LCD. This paper presents the technology needed to make in‐cell retarders and the performance of reflective and transflective LCDs with in‐cell retarders.     

Analysis,simulation, and evaluation of scrolling illumination as a method for reducing motion blur in LCOS projectors

Abstract— A high‐fidelity simulation of motion blurring in an LCOS projector was developed by using the measured temporal response of the projector. The simulation was validated for continuous and scanning illumination by comparison with results of motion‐blur measurements by using a pursuit camera. The simulation was then used to analyze and optimize duty cycle and phase parameters for scrolling illumination in the general case.     

A photographic technique for assessing the viewing‐angle performance of liquid‐crystal displays

Abstract— Liquid‐crystal displays (LCDs) have notable variation in luminance and perceived contrast as a function of the angle from which they are viewed. Though this is an important performance issue for LCDs, most evaluation techniques for assessing this variation have been limited to laboratory settings. This study demonstrates the use of a photographic technique for such an evaluation. The technique is based on an actively cooled charge‐coupled‐device (CCD) detector in combination with a macro lens covering a circular angular range (θ) of ±42.5°. The camera was used to evaluate the luminance and perceived contrast properties of an LCD. Uniform field images corresponding to 17 equally spaced gray‐scale values in the digital driving level (DDL) range of the display system were acquired. The 12‐bit gray‐scale digital images produced by the camera were converted to luminance units (cd/m²) via the measured luminance vs. DDL response function of the camera. The changes in perceived contrast as a function of viewing angle were derived from the Barten model of the gray‐scale response of the human‐visual system using the methods proposed by the AAPM TG18 Report. The results of this photographic technique were compared to measurements acquired from a similar display using a Fourier‐optics‐based luminance meter. The results of the two methods generally agreed to within 5%. The photographic methods used were found to be accurate and robust for in‐field assessment of the angular response of LCDs over the FOV of the camera.     

Deformed nanostructure of photo‐induced biaxial cholesteric films and their application in VA‐mode LCDs

Abstract— Novel biaxial retardation films made from photo‐induced deformed cholesteric liquid‐crystal (LC) nanostructures using reactive mesogen mixtures (RMMs) for a viewing‐angle compensation of vertically aligned liquid‐crystal displays (VA‐LCDs) was developed. The deformed cholesteric LC nanostructure has been observed by X‐ray‐diffraction (XRD) measurement. The birefringence of the film was described well by our optical model based on a form birefringence theory. The VA‐LCDs with photo‐induced biaxial cholesteric films have excellent viewing‐angle properties.     

Lapped transform‐based codec for frame‐memory reduction in super‐quality LCD overdrive

Abstract— Overdrive is commonly used to reduce the liquid‐crystal response time and motion blur in liquid‐crystal displays (LCDs). However, overdrive requires a large frame memory in order to store the previous frame for reference. In this paper, a lapped transform‐based codec (LTC) is proposed to reduce the frame memory needed for LCD overdrive. In the latest literature, a directional prediction‐based codec (DPC) employs eight directional predictions, which takes up a large percentage of the computational complexity of the codec and does not consider the de‐correlation of the inter‐blocks. Therefore, the LTC first uses the lapped transform to decompose the correlation of the inter‐blocks in the YUV color space. A hadamard transform is then used for energy compaction. The reordered coefficients are pre‐quantized and encoded using the proposed adaptive bit‐plane coding (ABPC) method for a simple hardware implementation. The simulation results show that the proposed LTC significantly improves the DPC in both subjective and objective performance and outperforms the block truncation coding (BTC) and adaptive multi‐level BTC (AM‐BTC), which have been described in the literature.     

A 6:1 image‐compression method using directional prediction for LCD overdrive

Abstract— An overdrive technology was developed and is widely used to diminish motion blur in LCDs. To store a previous frame in the overdrive operation in a limited‐sized memory, simple image‐compression techniques are required. By considering the strong correlation of nearby pixels in natural images, a new 6:1 color‐image‐compression method based on directional prediction is proposed. Different from the directional prediction of intra‐coding in H.264/AVC, the predictable direction is determined beforehand to minimize the computation complexity. A simple content‐adaptive quantization and bit‐streaming method, which preserves image details and is free from blocking artifacts, is also proposed. The experimental results show that our proposed method outperforms the vector quantization block truncation coding method with an average 3‐dB peak signal‐to‐noise ratio (PSNR) as well as the subjective quality in terms of blocking artifacts.     

Improving content visibility for high‐ambient‐illumination viewable display and energy‐saving display

Abstract— Nowadays, low‐contrast viewing of LC displays (LCDs) occurs very often, which includes the viewing of mobile LCDs at high ambient illumination and the viewing of LCDs at low‐power mode. These cases result in low‐content visibility and low contrast, leading to an unpleasant viewing experience. In this paper, a technique to improve the perceived contrast and visibility of images at low‐contrast viewing conditions is proposed. The proposed approach enhances image brightness with content and ambient adaptive image brightening and highlights visual parts and boundaries with non‐photorealistic rendering. The proposed technique enables longer battery life for mobile LC devices and makes mobile LC devices viewable at high ambient illumination. It also enables TVs with extreme low‐power consumption and smart‐grid responsive TVs.     

Guiding principles for high‐quality moving picture in LCD TVs

Abstract— The moving‐picture quality of several LCD modules was evaluated by using the quantitative parameter, normalized blurred edge width (N‐BEW), or the N‐BEW value normalized by time (N‐BET), measured and calculated by the developed time‐sequence‐image integration system which has taken LCD‐response characteristics and human‐vision characteristics into consideration. The quality of several LCD TVs is also discussed by using subjective evaluation and the unified quantitative parameter moving‐picture response time (MPRT), which is based on N‐BEW. According to the experimental and calculated results, it is clear that the value of N‐BET can express moving‐picture quality, which depends on the liquid‐crystal response time and the hold‐type character of LCDs. Also, it is confirmed that the value of MPRT can express the moving‐picture quality by comparison with subjective evaluation. The target values of MPRT and N‐BET for the motion‐blur‐less picture are deduced by extrapolating the subjective evaluation results. Then, guidelines to improve the moving picture quality are demonstrated.     

仿人机器人视觉导航中的实时性运动模糊探测器设计

针对仿人机器人视觉导航系统的鲁棒性受到运动模糊制约的问题,提出一种基于运动模糊特征的实时性异常探测方法. 首先定量地分析运动模糊对视觉导航系统的负面影响,然后研究仿人机器人上图像的运动模糊规律,在此基础上对图像的运动模糊特征进行无参考的度量,随后采用无监督的异常探测技术,在探测框架下对时间序列上发生的图像运动模糊特征进行聚类分析,实时地召回数据流中的模糊异常,以增强机器人视觉导航系统对运动模糊的鲁棒性. 仿真实验和仿人机器人实验表明:针对国际公开的标准数据集和仿人机器人NAO数据集,方法具有良好的实时性（一次探测时间0.1s）和有效性（召回率98.5%,精确率90.7%）. 方法的探测框架对地面移动机器人亦具有较好的普适性和集成性,可方便地与视觉导航系统协同工作.     

Comparisons of motion‐blur assessment strategies for newly emergent LCD and backlight driving technologies

Abstract— Compared to the conventional cathode‐ray‐tube TV, the conventional liquid‐crystal TV has the shortcoming of motion blur. Motion blur can be characterized by the motion‐picture response‐time metric (MPRT). The MPRT of a display can be measured directly using a commercial MPRT instrument, but it is expensive in comparison with a photodiode that is used in temporal‐response (temporal luminance transition) measurements. An alternative approach is to determine the motion blur indirectly via the temporal point‐spread function (PSF), which does not need an accurate tracking mechanism as required for the direct “spatial” measurement techniques. In this paper, the measured motion blur is compared by using both the spatial‐tracking‐camera approach and the temporal‐response approach at various backlight flashing widths. In comparison to other motion‐blur studies, this work has two unique advantages: (1) both spatial and temporal information was measured simultaneously and (2) several temporal apertures of the display were used to represent different temporal PSFs. This study shows that the temporal method is an attractive alternative for the MPRT instrument to characterize the LCD's temporal performance.     

Subjective evaluation of visual fatigue due to misalignment of motion and still images in a stereoscopic display

Abstract— In this paper, the relative influences of misalignment such as cross‐talk, vertical shift, and motion blur on visual fatigue by using a binocular stereoscopic display has been verified. Experiments were conducted for two cases: a still image and a motion image. They were evaluated by using the simulator sickness questionnaire (SSQ). By changing the disparity angle, cross‐talk, and vertical shift in the still‐image experiment, it was found that the SSQ score of each parameter increased as the amount of each factor increased. With a two‐sample t‐test between the presence and absence of each factor, a significant difference was found for the case of a more than 36‐arcmin disparity, more than 20% cross‐talk, and more than 10% vertical shift. In the motion‐image experiment, in which motion speed and the misalignment were varied, it was found that movement of the disparity angle caused much more visual fatigue in comparison with the misalignment factors, which were cross‐talk and vertical shift. In contrast, motion images in addition to the cross‐talk and/or vertical shift had a slight but unnoticeable relationship to an increase in visual fatigue. Therefore, it was concluded that vertical shift dominated the evaluation for still images, and the movement itself dominated the evaluation for motion images. The results suggest that it is necessary to evaluate visual fatigue according to the representing case, still or motion images, of a 3‐D stereoscopic display.     

Feature Detection Performance Based Benchmarking of Motion Deblurring Methods: Applications to Vision for Legged Robots

Dexterous legged robots can move on variable terrain at high speeds. The locomotion of these legged platforms on such terrain causes severe oscillations of the robot body depending on the surface and locomotion speed. Camera sensors mounted on such platforms experience the same disturbances, hence resulting in motion blur. This is a particular corruption of the image and results in information loss further resulting in degradation or loss of important image features. Although motion blur is a significant problem for legged mobile robots, it is of more general interest since it is present in many other handheld/mobile camera applications. Deblurring methods exist in the literature to compensate for blur, however most proposed performance metrics focus on the visual quality of compensated images. From the perspective of computer vision algorithms, feature detection performance is an essential factor that determines vision performance. In this study, we claim that existing image quality based metrics are not suitable to assess the performance of deblurring algorithms when the output is used for computer vision in general and legged robotics in particular. For comparatively evaluating deblurring algorithms, we define a novel performance metric based on the feature detection accuracy on sharp and deblurred images. We rank these algorithms according to the new metric as well as image quality based metrics from the literature and experimentally demonstrate that existing metrics may not be good indicators of algorithm performance, hence good selection criteria for computer vision application. Additionally, noting that a suitable data set to evaluate the effects of motion blur and its compensation for legged platforms is lacking in the literature, we develop a comprehensive multi-sensor data set for that purpose. The data set consists of monocular image sequences collected in synchronization with a low cost MEMS gyroscope, an accurate fiber optic gyroscope and an externally measured ground truth motion data. We make use of this data set for an extensive benchmarking of prominent motion deblurring methods from the literature in terms of existing and the proposed feature based metric.     

Registration Based Non‐uniform Motion Deblurring

This paper proposes an algorithm which uses image registration to estimate a non‐uniform motion blur point spread function (PSF) caused by camera shake. Our study is based on a motion blur model which models blur effects of camera shakes using a set of planar perspective projections (i.e., homographies). This representation can fully describe motions of camera shakes in 3D which cause non‐uniform motion blurs. We transform the non‐uniform PSF estimation problem into a set of image registration problems which estimate homographies of the motion blur model one‐by‐one through the Lucas‐Kanade algorithm. We demonstrate the performance of our algorithm using both synthetic and real world examples. We also discuss the effectiveness and limitations of our algorithm for non‐uniform deblurring.     

Photo-consistent synthesis of motion blur and depth-of-field effects with a real camera model

Depth-of-field (DOF) and motion blur are important visual cues used for computer graphics and photography to illustrate focus of attention and object motion. In this work, we present a method for photo-realistic DOF and motion blur generation based on the characteristics of a real camera system. Both the depth–blur relation for different camera focus settings and the nonlinear intensity response of image sensors are modeled. The camera parameters are calibrated and used for defocus and motion blur synthesis. For a well-focused real scene image, DOF and motion blur effects are generated by post-processing techniques. Experiments have shown that the proposed method generates more photo-consistent results than the commonly used graphical models.