Viewing direction measurements on flat and curved flexible E‐paper displays

The viewing direction characterization of reflective displays is more demanding than for emissive displays because defined illumination–detection geometries must be maintained for each viewing direction. In addition, the geometry should mimic the behavior of viewers who tend to exclude the reflection of light sources from a handheld reflective display. Viewing direction data was extracted from measured Bidirectional Reflectance Distribution Functions, showing that a source inclination of 45° sufficiently excludes the specular and haze components of source reflection from the measurement. Applying this so‐called 45/θ geometry to curved flexible displays is not straightforward since viewing direction, display curvature, and alignment each affect the measured reflectance. The viewing direction geometry proposed for convex cylindrical displays uses a ring light to deliver viewing‐direction independent illuminance, and maps the range of viewing directions onto the pixels of an image sensor. The illumination can also be applied to flat displays, allowing direct comparisons of flat and cylindrical display states. First results on e‐paper show good agreement with Bidirectional Reflectance Distribution Function data.     

Novel front‐light system using fine‐pitch patterned OLED

Abstract— A novel front‐light system that uses an organic light‐emitting‐diode (OLED) light source patterned with a fine pitch has been developed. The front‐light system has the following characteristics: (1) excellent uniformity within the light‐emitting area; (2) emittance that is consistent at all viewing angles; (3) no light leakage at any viewing angle from the side of the observer. This system can be adopted for reflective LCDs, electrophoretic displays (EPDs), microelectromechanical systems (MEMS), and other applications.     

Simulation and analysis of edge ghosting for microcapsule e-paper based on particle dynamics and light scattering model

Electronic paper (e-paper) is a reflective display technology with unique advantages, such as bistability, low-power consumption, and high ambient contrast ratio. These features make e-paper a promising candidate for future Internet of Things applications. Among different technologies of e-paper, electrophoretic display (EPD) is the most successful one for commercialization. However, the edge ghosting (also known as the fringing effect) still limits the performance of EPD. Herein, we established a model of particle dynamics of electrophoresis, simulated the edge ghosting of microcapsule EPD, analyzed the edge ghosting effect, and revealed the relationship between thicknesses, dielectric constants of the back binder layer, and the edge ghosting. Two EPD panels with different thicknesses of back binder layer were demonstrated, which verifies the accuracy of this simulation model. With the proposed model, many device mechanisms and product issues can be analyzed and illustrated, which is supposed to guide the researchers in optimizing the device structure design of EPD.     

Nanoparticle‐embedded polymer‐dispersed liquid crystal for paper‐like displays

Abstract— A polymer‐dispersed liquid‐crystal (PDLC) matrix template embedded with nano/microparticles can be backfilled/infiltrated with a dye‐doped liquid crystal for a paper‐like reflective display. In this way, a desirable degree of diffusion can be realized to reduce the viewing‐angle dependency of a gain reflector and metallic glare without changing other electro‐optical properties.     

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.     

Adapting softcopy color reproduction to ambient illumination

Abstract— The perceived colors of an image seen on a self‐luminous display are affected by ambient illumination. The ambient light reflected from the display faceplate is mixed with the image‐forming light emitted by the display. In addition to this direct physical effect of viewing flare, ambient illumination causes perceptual changes by affecting the adaptation state of the viewer's visual system. This paper first discusses these effects and how they can be compensated, outlining a display system able to adjust its output based on prevailing lighting conditions. The emphasis is on compensating for the perceptual effects of viewing conditions by means of color‐appearance modeling. The effects of varying the degree of chromatic adaptation parameter D and the surround compensation parameters c and N_c of the CIECAM97s color‐appearance model were studied in psychophysical experiments. In these memory‐based paired comparison experiments, the observers judged the appearance of images shown on an LCD under three different ambient‐illumination conditions. The dependence of the optimal parameter values on the level of ambient illumination was evident. The results of the final experiment, using a category scaling technique, showed the benefit of using the color‐appearance model with the optimized parameters in compensating for the perceptual changes caused by varying ambient illumination.     

Phosphors for plasma‐display panels: Demands and achieved performance

Almost two‐thirds of the discharge cells in plasma‐display panels (PDPs) are covered with phosphors. Beyond the efficient conversion of vacuum UV photons into visible light, the phosphor layer serves as a reflective mirror transporting light in the desired viewing direction. The quantum efficiency of state‐of‐the‐art PDP phosphors is, at its upper limit, 80–95%. Today's improved blue‐emitting BaMgAl₁₀O₁₇:Eu (BAM) phosphor still deteriorates during panel processing and operation, resulting in a loss of efficiency and color purity. A reduction in the phosphor particle size below 2 μm is suited to ease panel manufacturing and to improve light output.     

Stereo Light Probe

In this paper we present a practical, simple and robust method to acquire the spatially‐varying illumination of a real‐world scene. The basic idea of the proposed method is to acquire the radiance distribution of the scene using high‐dynamic range images of two reflective balls. The use of two light probes instead of a single one allows to estimate, not only the direction and intensity of the light sources, but also the actual position in space of the light sources. To robustly achieve this goal we first rectify the two input spherical images, then, using a region‐based stereo matching algorithm, we establish correspondences and compute the position of each light. The radiance distribution so obtained can be used for augmented reality applications, photo‐realistic rendering and accurate reflectance properties estimation. The accuracy and the effectiveness of the method have been tested by measuring the computed light position and rendering synthetic version of a real object in the same scene. The comparison with standard method that uses a simple spherical lighting environment is also shown.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

A high optical efficiency 3D/2D convertible integral imaging display

We propose a high optical efficiency three‐dimensional (3D)/two‐dimensional (2D) convertible integral imaging display by using a pinhole array on a reflective polarizer. The 3D mode is realized by adopting a pinhole array on a reflective polarizer to generate a point light source array. Three‐dimensional/2D convertible feature is realized by electrically controlling a polarization switcher. The reflective polarizer can reflect the light that has the orthogonal polarization direction with the reflective polarizer and transmit the light that has the same polarization direction with the reflective polarizer. The reflected light is recycled, so the optical efficiencies for both 3D and 2D modes are enhanced. In the practical experiments, the optical efficiencies of the proposed integral imaging display increase by 8.04 times and 1.65 times in 3D and 2D modes comparing with the conventional integral imaging display that has no light recycle, respectively.     

Viewing‐angle characterization of reflective‐type liquid‐crystal displays by using an ellipsoidal mirror and a two‐dimensional CCD camera

A new photometry to perform the viewing‐angle characterization for reflective‐type LCDs has been developed. The optics consists of a rotating ellipsoidal mirror and a 2‐D CCD camera. The information obtained by this photometry includes the viewing‐angle characteristics of reflectance, contrast ratio, and chromaticity coordinates, which are comparable to gonioscopic photometry in terms of accuracy. Both the illuminating polar angle and azimuth angle can be scanned. The measurement time for this method is as short as that for conoscopic photometry when using a 2‐D CCD camera. An instrument equipped with light‐polarizing devices is already available. If analytic software was available, viewing‐angle characterization could be determined by a polarization analysis.     

Measuring the effects of lighting on the readability of electronic devices

The aim of this study was to understand to what extent people can read e‐paper devices under various conditions of ambient illuminance that can occur indoors. In this study, 110 young to elderly subjects participated in an experiment to evaluate the effects of 14 different levels of ambient lighting on their reading from three different electronic devises and paper text. The participants were asked to undergo a timed read task and then to evaluate the readability of two eReader devices (a regular electronic display and one with a front light) in comparison with a backlit liquid crystal device and conventional paper text. The results indicated that backlit and front lit devices are easier to read at less than 200 lx and the reflective device is easier to read at levels above 500 lx.     

Novel concept for full‐color electronic paper

Abstract— Despite a steep increase in commercial devices comprising paper‐like displays, a much desired feature is still missing: bright full‐color electronic paper. A new reflective‐display technology has been developed to solve this issue. For the first time, the principles behind this in‐plane electrophoretic technology will be presented, which enables the realization of full‐color reflective displays with a higher brightness than presently available e‐paper technologies, without compromising paper‐like properties such as viewing angle and ultra‐low power consumption. An additional major advantage (e.g., for future low‐cost manufacturing) is that, besides direct‐drive and active‐matrix configurations, a passive‐matrix option with analog gray levels has been successfully developed.     

The Gyricon rotating ball display

Abstract— The Gyricon display consists of hemispherical black and white (bichromal) balls contained in individual liquid-filled cavities and disposed to orient in an electrical field. This bistable reflective light display currently has a diffuse reflectance of more than 18% and a contrast ratio of more than 6:1. The viewing angle approaches that of paper. A new method of fabricating the bichromal balls has enabled practical realization of large-area high-quality displays.     

Three‐dimensional pixel configurations for optical outcoupling of OLED displays—optical simulation

Because of considerations on image quality and fabrication/integration compatibility, current active‐matrix OLED displays (AMOLEDs) hardly adopt any effective light outcoupling techniques/structures, and it remains an unsolved critical technical issue. Recently, through optical simulation, we proposed a three‐dimensional (3D) pixel configuration as a potential and promising way to boost light outcoupling of OLED display pixels. By extending the bottom reflective electrode to bank slope of the pixel definition layer (PDL) and selectively filling the bank opening (concave area) with high‐index filler to form the optically reflective concave structure, it is possible to give several‐fold light extraction enhancement. In this paper, we further extend the simulation work by evaluating effects of more realistic graded bank slopes vs straight bank slope, less challenging nonpatterned (blanket) high‐index filler vs patterned filler, and real OLED layer stacks and properties. The optical simulation clearly reveals that light extraction enhancement can be mostly kept with more realistic graded bank profiles and even less ideal (but also less challenging) nonpatterned filler can provide substantial extraction enhancement. The graded bank structure also provides beneficial effects on viewing characteristics.     

Flexible hybrid substrates of roll‐to‐roll manufacturing for flexible display application

A flexible hybrid substrate was developed and demonstrated for roll‐to‐roll (R2R) manufacturing. Layer‐by‐layer misalignment can be well controlled within 5 µm. Top‐gate amorphous InGaZnO thin‐film transistor was fabricated on the flexible hybrid substrate by R2R process for the first time. A 4.3‐in. segment‐type reflective Electro‐Phoretic Display (EPD) display was also demonstrated to show the R2R capability of flexible substrates.     

Transfer printing for fabrication of flexible RGB color e‐paper

Electrophoretic display (EPD) has been a prevailing paper‐like display technology for years, owing to its advantages of flexibility, low‐power consumption, and good sunlight readability. However, it is regrettable that the black/white EPD still dominates the majority of the market while a commercially sold full‐color EPD is still unavailable. In this paper, we proposed a facile yet feasible method to fabricate a color EPD by a tape‐assisted transfer method, which is the first demonstration using transfer method to achieve color micro‐encapsulated EPD.     

High performance color‐converted micro‐LED displays

A full‐color micro‐LED display can be achieved by red, green, and blue (RGB) chips or by a blue/ultraviolet (UV) micro‐LED array to pump downconverters. The latter helps relieve the burden of epitaxial growth of tri‐color micro‐LED chips. However, such a color‐converted micro‐LED system usually suffers from color crosstalk and low efficiency due to limited optical density of color converters. With funnel‐tube array and reflective coating on its inner surface, the crosstalk is eliminated, and the optical efficiency can be improved by more than two times. In addition, the ambient contrast ratio is also improved because of higher light intensity. The color gamut of this device is approximately 92% of DCI‐P3 standard.     

Transflective IPS‐LCD with improved reflective contrast ratio

Abstract— In order to improve the reflective contrast ratio of transflective IPS‐LCDs, a novel pixel design for a normally white reflective IPS has been proposed. In this design, the large‐inter‐electrode‐spacing layout using a novel driving method and a double‐layered electrode have effectively reduced the light leakage. By applying these two technologies, a transflective IPS‐LCD has been successfully demonstrated with a high contrast ratio (15:1) in the reflective mode and a wide‐viewing‐angle characteristic in the transmissive mode.     

Using physically Based Rendering to Benchmark Structured Light Scanners

Structured light scanning is ubiquituous in 3D acquisition. It is capable of capturing high geometric detail at a low cost under a variety of challenging scene conditions. Recent methods have demonstrated robustness in the presence of artifacts due to global illumination, such as inter‐reflections and sub‐surface scattering, as well as imperfections caused by projector defocus. For comparing approaches, however, the quantitative evaluation of structured lighting schemes is hindered by the challenges in obtaining ground truth data, resulting in a poor understanding for these methods across a wide range of shapes, materials, and lighting configurations. In this paper, we present a benchmark to study the performance of structured lighting algorithms in the presence of errors caused due to the above properties of the scene. In order to do this, we construct a synthetic structured lighting scanner that uses advanced physically based rendering techniques to simulate the point cloud acquisition process. We show that, under conditions similar to that of a real scanner, our synthetic scanner replicates the same artifacts found in the output of a real scanner. Using this synthetic scanner, we perform a quantitative evaluation of four different structured lighting techniques – gray‐code patterns, micro‐phase shifting, ensemble codes, and unstructured light scanning. The evaluation, performed on a variety of scenes, demonstrate that no one method is capable of adequately handling all sources of error – each method is appropriate for addressing distinct sources of error.