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.     

A viewing‐angle‐controllable blue‐phase liquid‐crystal display

Abstract— A viewing‐angle‐controllable liquid‐crystal display (LCD) is proposed. When the device is only driven by an in‐plane electric field, it exhibits a wide‐viewing‐angle (WVA) mode. And it exhibits narrow‐viewing‐angle (NVA) mode when it is driven by a vertical electric field as well as an in‐plane electric field. In this manner, the viewing angle of the device can be controlled from 100° to 30°. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

Advanced impulsive‐driving technique for Super‐PVA panel

Abstract— Super‐PVA (S‐PVA) technology developed by Samsung has demonstrated excellent viewing‐angle performance. However, S‐PVA panels can place extra demands on charging time due to the time‐multiplexed driving scheme required to separately address two subpixels. Specifically, a 2G‐1D pixel structure theoretically requires subpixel charging in one‐half of the time available for a conventional panel. In this paper, a new LCD driving scheme, super impulsive technology (SIT), is proposed to improve motion‐blur reduction by driving an S‐PVA LCD panel at 120 Hz. The proposed scheme allows a 120‐Hz 2G‐1D panel to be driven with an adequate charging‐time margin while providing an impulsive driving effect for motion‐blur reduction. Considering that the cost of a 2G‐1D S‐PVA panel is comparable to that of a conventional 60‐Hz panel, this method achieves good performance at a reasonable price. The detailed algorithm and implementation method are explored and the performance improvements are verified.     

Circular camera array system for 3‐D displays based on the reconstruction of parallax rays

Abstract— A circular camera system employing an image‐based rendering technique that captures light‐ray data needed for reconstructing three‐dimensional (3‐D) images by using reconstruction of parallax rays from multiple images captured from multiple viewpoints around a real object in order to display a 3‐D image of a real object that can be observed from multiple surrounding viewing points on a 3‐D display is proposed. An interpolation algorithm that is effective in reducing the number of component cameras in the system is also proposed. The interpolation and experimental results which were performed on our previously proposed 3‐D display system based on the reconstruction of parallax rays will be described. When the radius of the proposed circular camera array was 1100 mm, the central angle of the camera array was 40°, and the radius of a real 3‐D object was between 60 and 100 mm, the proposed camera system, consisting of 14 cameras, could obtain sufficient 3‐D light‐ray data to reconstruct 3‐D images on the 3‐D display.     

Low‐leakage off‐angle in E‐polarizers

Abstract— New thin‐film polarizers have been developed for use in optical applications. The polarization technology is based upon liquid‐crystalline material built from dichroic dyes that can be deposited on virtually any substrate. Theoretical calculations and experimental results on viewing‐angle characterization of conventional O‐type polarizers and new E‐type polarizers are presented. At large viewing angles, the E‐type polarizers demonstrate lower light leakage, higher contrast ratio, and higher efficiency. Spectral performance depends on the composition of the dye mixture that is used to produce the polarizer coating. The new polarizers exhibit enhanced viewing angle and more design flexibility, providing new opportunities for the liquid‐crystal‐display industry.     

An integral‐imaging three‐dimensional display with wide viewing angle

Abstract— The viewing angle and flipping areas of a conventional integral‐imaging three‐dimensional (3‐D) display were analyzed. The pitches of the elemental image and micro‐lens are identical. The more micro‐lenses used, the smaller the viewing angle becomes and the wider the flipping areas become. In this paper, an improved integral‐imaging 3‐D display is presented. The pitch of the elemental image is larger than that of the micro‐lens. The single‐viewing angles of all micro‐lenses converge and there are no flipping areas at the optimal viewing distance. Computational reconstructions of improved and conventional integral imaging were carried out, and experimental results demonstrate that improved integral‐imaging 3‐D displays have a wider viewing angle than the conventional ones and do not have flipping areas at the optimal viewing distance.     

Optical characterization of autostereoscopic 3‐D displays

Abstract— Display‐measurement methods different from conventional 2‐D display measurements are needed for verifying the optical characteristics of autostereoscopic (3‐D) displays and for comparing different 3‐D display technologies. Industry is lacking standardized measurement methods, and the reported results can not always be compared. The selected set of characteristics discussed in this paper and partly defining the quality of the 3‐D experience are crosstalk, viewing freedom, and optimum viewing distance. Also, more conventional display characteristics such as luminance are discussed, since the definitions for these characteristics in 3‐D mode usually differ from those used for the 2D displays. We have investigated how these chosen 3‐D display characteristics can be objectively measured from transmissive two‐view and multiview 3‐D displays. The scope of this article is to generally define those basic characteristics as well as the different measurement methods. Most of the 3‐D characteristics can be derived from the luminance and colors versus the viewing angle. Either a conoscopic or a goniometric measurement system can be used, as long as the angular and stray‐light properties are suitable and known. The characteristics and methods are currently discussed in the display‐quality standardization forums.     

Analysis of longitudinal viewing freedom of reduced‐view super multi‐view display and increased longitudinal viewing freedom using eye‐tracking technique

Abstract— The viewing freedom of the reduced‐view super multi‐view (SMV) display was analyzed. It was found that there are separate multiple viewing ranges in the depth direction; thus, a technique that selects an appropriate viewing range to increase the longitudinal viewing freedom has been developed. Pixels of a flat‐panel display viewed by the viewer's eyes through a lenticular lens were determined from three‐dimensional (3‐D) positions of the viewer's eyes, which were obtained using an eye‐tracking system that employed a stereo camera. Parallax images corresponding to the 3‐D positions of the viewer's eyes were generated, which were displayed by the determined pixels. The experimental results show that the proposed technique successfully increased the longitudinal viewing freedom. It is also shown that a video camera was able to focus on the produced SMV images.     

Invited Paper: Depth reproducibility of multiview depth‐fused 3‐D display

Abstract— A multi‐view depth‐fused 3‐D (DFD) display that provides smooth motion parallax for wide viewing angles is proposed. A conventional DFD display consists of a stack of two transparent emitting screens. It can produce motion parallax for small changes in observation angle, but its viewing zone is rather narrow due to the split images it provides in inclined views. On the other hand, even though multi‐view 3‐D displays have a wide viewing angle, motion parallax in them is discrete, depending on the number of views they show. By applying a stacked structure to multi‐view 3‐D displays, a wide‐viewing‐angle 3‐D display with smooth motion parallax was fabricated. Experimental results confirmed the viewing‐zone connection of DFD displays while the calculated results show the feasibility of stacked multi‐view displays.     

A common approach to characterizing autostereoscopic and polarization‐based 3‐D displays

Abstract— Autostereoscopic and polarization‐based stereoscopic 3‐D displays recreate 3‐D images by providing different images in the two eyes of an observer. This aim is achieved differently for these two families of 3‐D displays. It is shown that viewing‐angle measurements can be applied to characterize both types of displays. Viewing‐angle luminance measurements are made at different locations on the display surface for each view emitted by the display. For autostereoscopic displays, a Fourier‐optics instrument with an ultra‐high‐angular‐resolution VCMaster3D is used. For polarization‐based displays, a standard Fourier‐optics instrument with additional glass filters is used. Then, what will be seen by an observer in front of the display is computed. Monocular and binocular quality criteria (left‐ and right‐eye contrast, 3‐D contrast) was used to quantify the ability to perceive depth for any observer position. Qualified monocular and binocular viewing spaces (QMVS and QBVS) are deduced. Precise 3‐D characteristics are derived such as maximum 3‐D contrast, optical viewing freedom in each direction, color shifts, and standard contrast. A quantitative comparison between displays of all types becomes possible.     

2‐D/3‐D switchable displays

Abstract— In this paper, the design of a lenticular‐based 2‐D/3‐D display for mobile applications is described. This display combines look‐around capability with good 3‐D resolution. In order to allow high‐resolution datagraphic applications, a concept based on actively switched lenses has been developed. A very noticeable problem for such displays is the occurrence of dark bands. Despite slanting the lenticular and defocusing the lens, banding becomes unacceptable when the display is viewed from an angle. As a solution, fractional viewing systems to reduce the banding intensity by almost two orders of magnitude is introduced. The resulting 3‐D display can be viewed from any horizontal direction without banding.     

High‐visibility 2‐D/3‐D LCD with HDDP arrangement and its optical characterization methods

Abstract— A 3.1‐in.‐diagonal 2‐D/3‐D LCD with a novel pixel arrangement, called horizontally double‐density pixels (HDDP), for high‐quality 3‐D images has been developed. 3‐D visibility has been improved by broadening the qualified stereoscopic viewing space (QSVS) where high‐quality 3‐D images can be seen. In order to evaluate the QSVS, optical characterization methods, based on the ergonomics for stereoscopy, such as 3‐D crosstalk, interocular luminance difference and 3‐D moiré have been proposed. The implementation results show that these methods can correctly evaluate high‐visibility autostereoscopic displays.     

Efficiency analysis for multi‐view spatially multiplexed autostereoscopic 2‐D/3‐D displays

Abstract— The wide‐viewing freedom often requested by users of autostereoscopic displays can be delivered by spatial multiplexing of multiple views in which a sequence of images is directed into respective directions by a suitable autostereoscopic optical system. This gives rise to two important design considerations — the optical efficiency and the resolution efficiency of the device. Optical efficiency is particularly important in portable devices such as cell phones. A comparison is given between lens and barrier systems for various spatial multiplexing arrangements. Parallax‐barrier displays suffer from reduced optical efficiency as the number of views presented increases whereas throughput efficiency is independent of the number of views for lens displays. An autostereoscopic optical system is presented for the emerging class of highly efficient polarizer‐free displays. Resolution efficiency can be evaluated by investigating quantitative and subjective comparisons of resolution losses and pixel appearance in each 3‐D image. Specifically, 2.2‐in.‐diagonal 2‐D/3‐D panel performance has been assessed using Nyquist boundaries, human‐visual contrast‐sensitivity models, and autostereoscopic‐display optical output simulations. Four‐view vertical Polarization‐Activated Microlens technology with either QVGA mosaic or VGA striped pixel arrangements is a strong candidate for an optimum compromise between display brightness, viewing angle, and 3‐D pixel appearance.     

Depth‐ and viewing‐angle‐enhanced 3‐D/2‐D switchable display system with high contrast ratio using multiple display devices and a lens array

Abstract— An improved 3‐D/2‐D switchable display system with enhanced depth and viewing angle by adding two LCD panels to an integral imaging system has been realized. The proposed system uses the see‐through property of an LCD panel and displays multiple sets of elemental images on the LCD panels to integrate them on multiple locations simultaneously. As a result, the depth of the 3‐D image can be enhanced. For wide viewing angles, the time‐multiplexing method was adopted by displaying mask patterns on the front LCD panel. In addition, another technique to increase the contrast ratio of the proposed system has also been developed. Some experimental results will be provided.     

A continuous‐viewing‐angle‐controllable liquid‐crystal display using a blue‐phase liquid crystal

Abstract— A continuous‐viewing‐angle‐controllable liquid‐crystal display (LCD) using a blue‐phase liquid crystal is proposed. To realize both wide‐viewing‐angle (WVA) mode and narrow‐viewing‐angle (NVA) mode with a single liquid‐crystal panel, each pixel is divided into a main pixel and a subpixel. The main pixel is for displaying images in both modes. The subpixel is for displaying images in WVA mode and controlling the viewing angle in NVA mode. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

Viewing‐angle‐switching device based on array of optical micro‐rods incorporated with electrophoretic material systems

We have successfully demonstrated a control device for a viewing angle that enables switching between two states, a wide‐viewing angle, and a narrow‐viewing angle. It is composed of a light‐transmitting portion formed with an array of optical micro‐rods and a shielding/transmitting changeable portion of cross stripes designed with electrophoretic material systems consisting of black particles and an optically transparent medium. When the black particles are fully dispersed in the optically transparent medium, the cross stripe portion plays the role of a non‐transmitting material as the shielding portion in a similar manner to a conventional viewing angle control film. When the black particles are completely gathered electronically to one side in the optically transparent medium, in contrast, the cross stripe portion filled by the optically transparent medium can transmit incident light. These functions allow us to select electrically either of two modes between a limited viewing angle and a non‐limited viewing angle. The optical properties for the limited viewing angle mode were +/?30° of the visible angle and 50% of the transmittance, and the one for the non‐limited viewing mode was 58% of the transmittance. The response time from the narrow‐viewing angle to wide‐viewing angle was 1 s at 20 V of applied voltage.     

Noise estimation and reduction on five medical liquid‐crystal displays

Abstract— Liquid‐crystal displays (LCDs) are replacing cathode‐ray tube (CRT) displays as primary diagnostic viewing devices in clinics. They exhibit higher spatial noise than CRTs, which can interfere with diagnosis and reduce the efficiency especially when subtle abnormalities are presented. A study by the authors on LCD spatial noise has recently been reported. A high‐quality CCD camera was used to acquire images from the LCD. Noise properties were estimated from the digital‐camera images. Then, an error‐diffusion‐based operation was applied to reduce the display spatial noise. This paper presents the noise estimation and reduction results on five different medical‐grade LCDs using the same study protocol. These five different LCDs vary in terms of matrix size, pixel size, pixel structure, and vendors. The purpose of this work is to demonstrate that the LCD spatial‐noise estimation and reduction scheme proposed earlier by the authors is valid, robust, and necessary for various medicalgrade LCDs used in clinics today.     

Light‐scattering liquid‐crystal composites with reduced off‐axis haze

Abstract— The majority of liquid‐crystal (LC) composites operating in a light‐scattering mode suffer from scattering of the obliquely incident light in the field on‐state (off‐axis haze effect). This is evident in the angularly selective viewing‐angle characteristic with a maximal transmittance corresponding to the normally incident light. We consider methods to control the viewing‐angle characteristic of polymer‐dispersed LC (PDLC) and filled LC. For PDLC samples, this control is realized by modification of the refractive index of the polymer matrix with highly refractive nanoparticles (NP) having a low rate of aggregation in the polymer. By proper optimization of NP concentration, one can bring the refractive index of the polymer matrix in the range needed to reduce the haze problem. In filled LC, the viewing‐angle curve depends on the refractive‐index mismatch between the LC and NP. By optimization of this parameter, one can flatten the angular characteristic or obtain selectable viewing angles in the desirable range. These results allow for the construction of optical shutters and a scattering‐type LCD with controllable viewing‐angle characteristics, particularly with low off‐axis haze.     

Optical design and roll‐to‐roll fabrication process of microstructure film for wide viewing LCDs

We have developed a new microstructure film for wide viewing liquid crystal displays (LCDs). By attaching it to the surface of a conventional LCD, the viewing angle characteristics of LCD has drastically improved without causing a blur of the frontal image and a decrease in the contrast ratio under bright ambient light conditions. This film can be applied to various LC modes including twisted nematic and multidomain vertical alignment by changing its internal micrometer‐size 3D structure. Further, this film can be mass‐produced efficiently by self alignment roll‐to‐roll process.     

Reconstruction of 3D contour with an active laser‐vision robotic system

This paper presents a 3D contour reconstruction approach employing a wheeled mobile robot equipped with an active laser‐vision system. With observation from an onboard CCD camera, a laser line projector fixed‐mounted below the camera is used for detecting the bottom shape of an object while an actively‐controlled upper laser line projector is utilized for 3D contour reconstruction. The mobile robot is driven to move around the object by a visual servoing and localization technique while the 3D contour of the object is being reconstructed based on the 2D image of the projected laser line. Asymptotical convergence of the closed‐loop system has been established. The proposed algorithm also has been used experimentally with a Dr Robot X80sv mobile robot upgraded with the low‐cost active laser‐vision system, thereby demonstrating effective real‐time performance. This seemingly novel laser‐vision robotic system can be applied further in unknown environments for obstacle avoidance and guidance control tasks. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society