LC Panel Research Articles

78‐3: A Tristimulus Electro‐optical Model Describing Interactions of a RGB Backlight Unit and an LC Panel

Describing the behavior of an RGB backlight is complex but crucial in applications as local dimming with a variable backlight color. A color model to describe the interaction of the spectral backlight composition and the LC panel is the scope of this paper. The output of the model extends the commonly used one‐dimensional luminance to three‐dimensional tristimulus. Such a model requires that the physical characteristics of the RGB BLU as well as the LC‐panel are considered. The input variables include beyond the RGB subpixel gray values also the three duty ratios for the RGB‐LEDs. The calculation of the XYZ coordinates of an LC pixel, while an RGB backlight is varied, may get feasible. Also, a method for parameter extraction will be shown.

CNN-based image splitting algorithm for dual-layer display

Dual-layer displays (DLDs) can achieve high dynamic range by reducing light leakage via bonding two LC panels. However, the physical distance between the two LC panels introduces a parallax error when the display is viewed off-axis. This paper proposes a convolutional neural network-based image splitting algorithm for improving the display quality of a DLD. In order to improve processing speed, the network structure is designed relatively simply. The training dataset is established mainly based on TV signals. Different from the common image evaluation metrics based on PSNR and SSIM, the paper proposes to apply learned perceptual image patch similarity (LPIPS) to define the loss function for DLDs. The simulation and experiment results show that compared with the existing method, the proposed method has better performance in reducing parallax error and improving image details. The processing time can be shortened by 2.7 times. The proposed CNN-based method can greatly reduce the processing time while maintaining high display quality, which presents high practicability.

P‐8.2: CNN for Dual‐layer LCDs

Low contrast ratio (CR) is one big drawback for LCD, which is caused by light leakage of LC cell. Light leakage can be greatly reduced by bonding two LC panels to form a dual‐layer LCD. However, with the certain distance between the two LC panels, the ghost may appear when viewing off‐axis. This paper proposes a convolutional neural network‐based method to improve the display quality of a dual‐layer LCD. The network consists of 8 convolution layers, in which the kernel of the layer 4 and layer 8 is 1×1 to eliminate the redundant features and accelerate the processing speed. The kernel of the other layers is 3×3. Concat1 and Concat2 are included to fuse the features from the convolution layer 1‐3 and 5‐7. The loss function is especially defined with the consideration of the total differences between the reconstructed images at the different viewing angles and the input image. The simulation results show that compared with the existing methods, the proposed method has the merits of higher display quality and shorter processing time, which presents high practicability.

Investigating the effect of gravity on the optical performance of large-sized liquid crystal displays

This paper proposes a method to investigate the effect of gravity on optical performance of large-sized liquid crystal displays (LCDs). Combined with the finite element analysis and the LCD optical simulation, the change in optical performance of large-sized LCDs under the influence of gravity is analyzed. Compared with the condition without tilt angle, the Δu'v' is 0.025 in the bottom area of the 100-in LCD with the substrate thickness of 0.3 mm at a tilt angle of 1.5°, leading to a noticeable color shift. With the decrease of tilt angle or the increase of substrate thickness, the change in optical performance becomes unnoticeable and thus avoids the occurrence of visible display defect. Utilizing the proposed method, the assembly precision of large-sized LC panels can be calculated and the display defect caused by gravity can be effectively prevented.

P‐3.1: Convolutional Neural Network based Image Segmentation Algorithm for Dual‐Layer LCDs

Dual-layer LCDs have the advantage of high contrast ratio, but due to the physical distance between the two LC panels, parallax error may appear when viewed off-axis, affecting the display quality. In this paper, we propose a convolutional neural network-based algorithm to mitigate parallax error and improve the display quality. First, a suitable training data set is selected and the input image is processed by a convolutional neural network to output a front image and a rear image. These two images are staggered and multiplied to obtain reproduced images at different angles. The reproduced image is compared with the original image by means of a loss function, and the parameters in the convolution are continuously updated to achieve the best display quality. The algorithm proposed in this paper can effectively mitigate the parallax error phenomenon of a dual-layer LCD and improve the display quality, and the computational efficiency is also higher than the traditional algorithms.

46‐4: High Frame Rate Scanning Backlight System For Gaming PC Display with IGZO‐TFT Technology

The rapid expansion of the gaming PC market in recent years has increased the demand for high frame rate display modules. Especially for laptops, the demand for thinner profiles and narrower borders also continues to be strong. We have developed an LCD module with a combination of a high frame rate LC panel based on IGZO‐TFT technology and a scanning backlight that enables high moving picture quality in a thin profile with narrow borders on three sides. The scanning backlight has fewer segmented areas. Nevertheless, our LCD achieves higher moving picture quality by using a fast response LC.

Analyzing the effect of temperature on optical performance of dual‐layer liquid crystal displays

AbstractThe effect of temperature on optical performance of a dual‐layer liquid crystal display (LCD) is investigated by considering LC material parameter and structural deformation of LC panels simultaneously. First, the optical anisotropy of LC material under the influence of temperature is calculated theoretically. Then, the thermal deformations of the dual‐layer LC panels caused by temperature are simulated. Combined with the two factors, the change in optical performance of a dual‐layer LCD under the influence of temperature can be analyzed. In white state, the color in the central area of a dual‐layer LCD is shifted towards blue, and a yellowish border in the edge area may appear. In gray or black state, there may be a light leakage in the edge area of a dual‐layer LCD under the influence of temperature.

Programmable Liquid Crystal Apertures and Filters for Photographic Lenses

LCDs (Liquid Crystal Displays) have become the ubiquitous low-cost display technology, with full color displays offering good resolution costing less than $10. Although LCD modules generally include either a backlight or a reflective backing, the LC panel itself merely modulates light by altering polarization. Thus, it is possible to use a transmissive LC panel as a programmable optical filter, or LCLV (Liquid Crystal Light Valve). This paper explores a variety of potential uses of commodity LC panels, including color panels, to implement programmable apertures and filters for camera lenses.

Integrating Backlight With Color-Filter-Free Panel for Enhancing Performance of LCD

In this study, we proposed an innovative concept of integrating a polarized color-separating backlight with a color-filter-free LC panel for enhancing performance of the curved LCD system. We design a two-level folded backlight to exploit the light sources LEDs with color enhancement by quantum-dot technology to produce color beams emerging at separate angles with a linearly polarizing state. The integrated LC panel focuses the separating color beams onto the corresponding subpixels with no need of the color filter; redirects the color beams at respective angles into the normal and reforms their angular shapes to be identical for attaining good color uniformity in the viewing cone. We established a system model for simulation to evaluate its performance. According to the simulation results, it performs the high optical efficiency of 33.75% that is about four times the traditional LCD, and displays color gamut of 94.1% NTSC (CIE 1931). It also provides the illuminance uniformity of 90% above and good color uniformity in both the spatial space and angular space of the viewing cone with horizontal and vertical angular widths of 100o and 75o, respectively. Furthermore, the simulation results demonstrate that the design can apply to a 55-inch curved LCD and further extend the maximum diagonal size up to 88 inches while keeping slim volume with a minimal thickness of 6.5 mm.

Liquid Crystal Displays with Variable Viewing Angles Using Electric-Field-Driven Liquid Crystal Lenses as Diffusers

We propose a novel method for appropriately controlling the luminance distribution of liquid crystal displays (LCDs) for different usage environments by using electric-field-driven liquid crystal (ELC) lenses. The LCD systems are composed of quasi-collimated backlights (QCBLs), LC panels, and ELC lenses that are used as diffusers. To achieve a wide viewing angle, light is diffused with the ELC lenses by controlling its retardation with the voltage applied to the electrodes. For private use, a narrow viewing angle is achieved by turning the ELC lenses off so that the collimated light from the QCBLs passes directly through the liquid-crystal layer of the ELC lens and travels without diffusion. To validate the proposed method, we simulated the luminance distributions of the wide-view and narrow-view modes by using a finite difference method (FDM) and Taguchi’s design of experiments method. The simulation results show that the light distribution of the wide-view mode was 84.3% similar to the ideal Lambertian distribution and was wider than that of IPS-LCDs with wide viewing angle characteristics. In addition, the light distribution of the narrow-view mode had a full width at half maximum of 7°. The luminance of the exiting light at viewing angles of 20° and above was calculated to be close to 0.

P‐152: Analysis and Comparison of Display Defects of Rugged LCDs in high temperature environment

To guarantee the display quality in harsh environment, a LCD in military application has to be ruggedized via bonding an ITO glass to reduce electromagnetic interference and reflection. However, with the same bonding process, the rugged LCDs using the LC panels from some manufacturers become more easier to display Mura than the panels from other manufacturers. The paper proposes an experiment‐and‐simulation‐combined method to analyze the display defects of the rugged LCDs. 2 kinds of the common LCDs and the rugged LCDs were tested and simulated. It is found that one kind of the common LCD and the rugged LCD is more sensitive to the external force and temperature, leading to higher possibility to display Mura. It would be helpful to perform some tests on common LCDs before ruggedization to choose one that is no sensitive to harsh environment.

Paper] Design of VA-LCD System with Microstructure Film for Wide Viewing

We have developed a wide viewing VA-LCD system with the microstructure film. This film is attached on LC panel and scatters incident lights from LC panel by reflection at internal air cavities to improve the viewing angle characteristics. In this system, we have optimized LC alignment directions and BL distribution as well as the scattering profile of the film. LC panel has two-domain LC aligned pixel (each LC director is antiparallel in vertical direction) and wide viewing angle in horizontal direction. Backlight distribution is collimated to horizontal direction. To distribute lights in horizontal direction to vertical direction, we designed and fabricated the microstructure film which had rhombus shaped air cavities. This display system indicated smaller color shift and higher CR at oblique angles than the conventional VA-LCD; the color shift from the normal direction (Δu'v') at θ= 60° was reduced by 60% and the CR was over 100:1 at all directions.

59-1:Invited Paper: Modeling and Suppressing of Color Breakup

Field-sequential color displays are used as an alternative to the standard displays where energy consumption can be reduced or peak luminance can be increased. Its spatial resolution is potentially three times higher compared to a conventional color filter LCD. The concept of field sequential color displays shows the problem of color breakup artifact. This paper reviews the cause and the factors for the perception of color breakup, discusses the approaches for the reduction of color breakup. It is suggested that, with field-sequential color algorithm, 180Hz or 240Hz LC panel could have potential market in the high luminance and high resolution display applications.

Planar apparatus for uniformly emitting light with angular color-separation.

This study proposes a slim planar apparatus that can function as a color-separation backlight for the color-filter-free liquid-crystal display (LCD) system. It has a two-level folded configuration comprising a composite light-guide plate (LGP) and light-emitting diode (LED) couplers. The LED couplers generate the highly collimated beams of the three primaries (R, G, and B) that enter the composite LGP at their separate angles; then the three primaries were uniformly extracted out of the top surface of the LGP at their respective angles differing in the longitudinal direction. In the simulation, a lenticular lens array was used to focus the three primaries onto their respective subpixels; each pixel of the LC panel comprised three subpixels, identical to the traditional layout. The proposed apparatus can be applied in backlight modules with a maximal diagonal dimension of 39 inches and a thickness of 15.5 mm. The simulation results indicated that the spatial uniformities of the three primaries ranged between 84% and 87%, the area of the color gamut of the LCD system was 99.5% of that defined by the National Television System Committee, and the total optical efficiency was 41%, as the double of a traditional LCD system. Thus, the proposed apparatus improved the total optical efficiency markedly and provided the LCD system with a wide color gamut.

Fast-Response Blue-Phase Liquid Crystal for Color-Sequential Projection Displays

Color sequential projection display using a vertical field switching (VFS) polymer-stabilized blue phase liquid crystal (BPLC) is proposed. The VFS-BPLC exhibits submillisecond response time which is useful for suppressing color breakup. The proposed projector also has a small throw ratio. With phase compensation, the distortion from oblique LC panel could be corrected.

P‐163: Three‐terminal Dye‐doped LC Device Switchable between Reflective and Transmissive Modes

AbstractWe propose a three‐terminal dye‐doped LC device that is switchable between reflective and transmissive modes without image inversion. An additional LC panel or optical components are not needed for the proposed device, differently from conventional mode‐switchable LCDs. Compared to the previous dual panel structure consisting of two vertically‐aligned LC layers, an enhancement of the transmittance by more than 4% was obtained because there is no increase in the light absorption by an additional LC panel.

P‐117: Viewing Angle Switchable LCD Based on Kerr Effect

AbstractWe propose viewing angle switchable liquid crystal displays (LCDs) with optically isotropic liquid crystal mixture such as polymer‐stabilized blue phase (PSBP) LC and nano‐structured LC. The devices are featured by two concepts: (1) using one panel, a pixel is divided into two parts; main pixel being in charge of displaying main images and sub pixel for controlling viewing angle, (2) using two panels; one panel is nematic LC panel which displays main images and the other is PSBP LC panel which controls viewing angle. In both devices, main information is interrupted at off‐normal direction by light leakage and luminance control, respectively. By controlling the applied voltages in sub pixel and PSBP LC panel, wide viewing angle can be switched to narrow viewing angle.

78.3: Dual Mode Projection Display System for Mobile Devices

AbstractWith removing the LC panel from a conventional portable device, we proposed an innovative dual‐mode projection display system combining pico projector technology and rear display technologies, including a wedge display feature and a reflective air chamber feature, to provide switchable display modes for front, rear or front‐rear projection operations in one portable device.

Dual Layer LC Panels for Polarization Control to Display Invisible 2D Code

The authors have researched a support system of the reminiscence and life review activity. This support system consists of an interactive tabletop display and interface system. An invisible code is one of the useful technologies. The invisible codes provide us with an operating environment using a pen-like device. However, this technology is applied to the only paper media. The authors think we want to realize an interaction using the invisible code on an electrical media. We propose a method to display invisible codes using LCD panels and to detect a polarized symbol image with a conventional CCD camera.

Color Breakup Reduction by 180 Hz Stencil-FSC Method in Large-Sized Color Filter-Less LCDs

Field-sequential color (FSC) is a high optical throughput technique for future green liquid crystal displays (LCDs). However, the FSC-LCD faces a lethal issue, color breakup (CBU) which degrades image clarity and prevents high level LCD-TV productions. We proposed the 180 Hz Stencil Field-Sequential-Color method to redistribute intensities of the three primary color field-images to suppress CBU. By applying local color-backlight-dimming technology to FSC-LCDs, a low resolution colorful backlight panel combined with a high resolution color filter-less LC panel generated a green-based multi-color field-image which showed the most image luminance in the first field. Therefore, residual red and blue field-image intensities were reduced and effectively suppressed CBU when compared to field-rate increasing methods. In addition, to further implement hardware, the number of backlight divisions of 32×24 and a proper Gaussian point spread function profile were optimized via simulations while considering CBU reduction and image fidelity. Using optimized hardware parameters, the CBU phenomenon was suppressed by 50% of traditional RGB driving in simulation and was demonstrated on a 120 Hz 46-inch MVA LCD-TV.