Performance evaluation of multi‐primary color‐matrix layouts for mobile displays

Abstract— Different subpixel layouts for multi‐primary displays will be presented and their spatial performance analyzed. The layouts studied include red, green, blue, yellow, and cyan subpixels, arranged in 5/5, 5/4, and 5/3 configurations. In the 5/5 configuration, five primaries are arranged on five subpixels forming a square pixel. In the 5/4 configuration, five primaries are arranged on two square units, each of which have four subpixels so that the cyan and yellow subpixels are missing in alternate pixels. In the 5/3 layout, the multi‐primary color matrix is placed on top of a standard RGB TFT backplane with a subpixel aspect ratio of 1:3, resulting in an increased period of the full color sequence. Different data‐rendering methods for the modified color sequences were studied and their implication on the spatial performance were analyzed, given in terms of reproduction accuracy, i.e., the average S‐CIELAB error between data reproduced on a reference display and that reproduced on the examined layout. The reproduction error as a function of the angular substance of a pixel is reported for different layouts and rendering methods and are compared to that of an RGB display. It will be shown that the modified multi‐primary layouts reduce power consumption and provide good image quality for mobile applications.     

The luminance resolution characteristics of multi‐primary‐color display

Abstract— In this paper, the resolution characteristics of multi‐primary‐color (MPC) display systems are analyzed. That four‐primary‐color (4PC) displays can increase the effective resolution for achromatic images in the luminance domain by a factor of two as compared to conventional RGB‐based displays with MPC‐specialized subpixel rendering, which is proposed in this paper, is demonstrated. Five‐ and six‐primary‐color (5PC and 6PC) display systems can reproduce denser luminance data than conventional RGB‐based display systems and solve a problem of MPC displays, viz. an increase of production costs and a decrease in the aperture ratio caused by increasing the number of subpixels in one pixel. This is an essential advantage of MPC display systems, which is related to the combination of the proposed color‐filter architecture and image processing. Thus, a completely new advantage of MPC display systems, in addition to their well‐known capabilities of color reproduction and power saving, is proposed.     

Active‐matrix organic light‐emitting displays employing two thin‐film‐transistor a‐Si:H pixels on flexible stainless‐steel foil

Abstract— An active‐matrix organic light‐emitting diode (AMOLED) display driven by hydrogenated amorphous‐silicon thin‐film transistors (a‐Si:H TFTs) on flexible, stainless‐steel foil was demonstrated. The 2‐TFT voltage‐programmed pixel circuits were fabricated using a standard a‐Si:H process at maximum temperature of 280°C in a bottom‐gate staggered source‐drain geometry. The 70‐ppi monochrome display consists of (48 × 4) × 48 subpixels of 92 ×369 μm each, with an aperture ratio of 48%. The a‐Si:H TFT pixel circuits drive top‐emitting green electrophosphorescent OLEDs to a peak luminance of 2000 cd/m².     

Active matrix monolithic micro‐LED full‐color micro‐display

An active matrix monolithic micro‐LED full‐color micro‐display with a pixel density of 317 ppi is demonstrated. Starting from large‐scale and low‐cost GaN‐on‐Si epilayers, monolithic 64 × 36 blue micro‐LED arrays are fabricated and further transformed to full‐color micro‐displays by applying a photo‐patternable color conversion layer. This full‐color fabrication scheme shows feasible manufacturability, suggesting a potential for volume production of micro‐LED full‐color micro‐display.     

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.     

High‐luminance 1.8‐mm‐pixel‐pitch CNT‐FED for ubiquitous color character displays

Abstract— A high‐luminance 1.8‐mm‐pixel‐pitch CNT‐FED for color character displays has been developed. The display panel has 32 × 256 color pixels, and the subpixel size is 0.6 × 1.8 mm. The display panel can provide good visibility when installed even in outdoor locations. The power consumption is low enough for the display to be battery driven. The practical application is the display of important messages regarding the evacuation from disaster areas, even under emergent no‐power conditions similar to the messages on vending machines.     

High‐quality direct‐view display combining multiple integral 3D images

This paper proposes a method for combining multiple integral three‐dimensional (3D) images using direct‐view displays to obtain high‐quality results. A multi‐image combining optical system (MICOS) is used to enlarge and combine multiple integral 3D images without gaps. An optical design with a simple lens configuration that does not require a diffuser plate prevents the deterioration in resolution resulting from lens arrangement errors and the diffuser plate. An experiment was performed to compare a previously developed method with the proposed method, and the latter showed a significant improvement in image quality. A method for expanding the effective viewing angle of the proposed optical design was also developed, and its effectiveness was confirmed experimentally. A prototype device of the proposed optical design was constructed using a high‐density organic light‐emitting diode (OLED) panel with 8K resolution and 1058 ppi pixel density to achieve 311 (H) × 175 (V) elemental images, a viewing angle of 20.6° in both the horizontal and vertical directions, and a display size of 9.1 in. In addition, the proposed optical design enabled making device considerably thinner, ie, with a thickness of only 47 mm.     

Subpixel image scaling for color‐matrix displays

Abstract— The perceived resolution of matrix displays increases when the relative position of the color subpixels is taken into account. “Subpixel‐rendering” algorithms are being used to convert an input image to subpixel‐corrected display images. This paper deals with the consequences of the subpixel structure and the theoretical background of the resolution gain. We will show that this theory allows a low‐cost implementation in an image scaler. This leads to high flexibility, allowing different subpixel arrangements and a simple control over the trade‐off between perceived resolution and color errors.     

Inverse display characterization: A two‐step parametric model for digital displays

Abstract— A simple additivity model is often used as a basic model for digital‐display characterization. However, such a simple model cannot satisfy the needs of demanding color‐management applications all the time. On the other hand, systematic sampling of the color space and 3‐D interpolation is an expensive method in terms of measurement and computation time when precision is needed. This paper presents an enhanced method to characterize the XYZ‐to‐RGB transform of a digital display. This parametric method exploits the independence between the luminance variation of the electro‐optic response and the colorimetric responses for certain display types. The model is generally applicable to digital displays, including 3‐DMD projectors, single DMDs, CRTs, LCDs, etc., if the independence condition is satisfied. While the problem to solve is a 3‐D‐to‐3‐D transformation (from XYZ to RGB), the proposed parametric model is the composition of a 2‐D transform followed by a 1‐D transform. The 2‐D transform manages the chromatic aspects and, in succession, the 1‐D transform manages the luminance variations. This parametric digital model is applicable in the field of color management, with the objective of characterizing digital displays and applying a reference look such as a film look.     

Fabrication of a 7.6‐in.‐diagonal prototype ballistic electron surface‐emitting display on a glass substrate

Abstract— A prototype ballistic electron surface‐emitting display (BSD) was fabricated on a TFT or PDP glass substrate by using a low‐temperature process. A 84 × 63‐pixel, 7.6‐in.‐diagonal full‐color BSD shows excellent performance, comparable to the previously reported 2.6‐in. model. This result demonstrates the strong possibility of large‐panel BSDs.     

Optical simulation for cross‐talk evaluation and improvement of autostereoscopic 3‐D displays with a projector array

Abstract— Multi‐view spatial‐multiplexed autostereoscopic 3‐D displays normally use a 2‐D image source and divide the pixels to generate perspective images. Due to the reduction in the resolution of each perspective image for a large view number, a super‐high‐resolution 2‐D image source is required to achieve 3‐D image quality close to the standard of natural vision. This paper proposes an approach by tiling multiple projection images with a low magnification ratio from a microdisplay to resolve the resolution issue. Placing a lenticular array in front of the tiled projection image can lead to an autostereoscopic display. Image distortion and cross‐talk issues resulting from the projection lens and pixel structure of the microdisplay have been addressed with proper selection of the active pixel and adequate pixel grouping and masking. Optical simulation has shown that a 37‐in. 12‐view autostereoscopic display with a full‐HD (1920 × 1080) resolution can be achieved with the proposed 3‐D architecture.     

Low‐Cost Subpixel Rendering for Diverse Displays

Subpixel rendering increases the apparent display resolution by taking into account the subpixel structure of a given display. In essence, each subpixel is addressed individually, allowing the underlying signal to be sampled more densely. Unfortunately, naïve subpixel sampling introduces colour aliasing, as each subpixel only displays a specific colour (usually R, G and B subpixels are used). As previous work has shown, chromatic aliasing can be reduced significantly by taking the sensitivity of the human visual system into account. In this work, we find optimal filters for subpixel rendering for a diverse set of 1D and 2D subpixel layout patterns. We demonstrate that these optimal filters can be approximated well with analytical functions. We incorporate our filters into GPU‐based multi‐sample anti‐aliasing to yield subpixel rendering at a very low cost (1–2 ms filtering time at HD resolution). We also show that texture filtering can be adapted to perform efficient subpixel rendering. Finally, we analyse the findings of a user study we performed, which underpins the increased visual fidelity that can be achieved for diverse display layouts, by using our optimal filters.     

Practical CNT‐FED structure for high‐luminance character displays

Abstract— A high‐luminance CNT‐FED character display using a simple line rib structure was constructed. The display panel had 48 × 480 dots and the subpixel pitch was 1 mm. The greatest benefit of a display using CNT technology is high luminance performance with low‐power consumption. The luminance of the green‐color dot wasca. 10,000 cd/m² under 1/1 6 duty‐cycle driving at a 6‐kV anode voltage. The high luminance of the display panel can provide good visibility when installed even in outdoor locations, and the power consumption was ca. 4 W at the character displaying module. This, a CNT‐FED for character displays also has potential multifunctionality, which could be battery driven. It should be useful for public displays even under emergency no‐power conditions. In this work, a practical structure and process technologies for making ribs with reasonable cost were developed. The newly introduced 2‐mm‐tall line ribs as spacers were formed by using innovative production processes; i.e., the rib paste was pushed out of a multi‐slit nozzle, and the rib shape was formed by UV‐light irradiation. The developed panel structure and manufacturing processes also had the advantages of size flexibility and high production yield.     

Projection‐type integral 3‐D display with distortion compensation

Abstract— Our research is aimed at developing a spatial‐imaging‐type integral three‐dimensional (3‐D) display based on an integral photography method using an extremely high‐resolution projector. One problem with the projection‐type integral 3‐D display is that geometrical distortion in projected elemental images causes spatial deformation of the displayed 3‐D image. In this study, a general relationship between the geometric distortion of elemental images and the spatial deformation of reconstructed 3‐D images were analyzed. A projection‐type integral 3‐D display with a distortion compensator which corrects the geometrical distortions of projected images in real‐time have been developed. The deformation of the displayed 3‐D images was significantly reduced by the distortion compensation, and the displayed 3‐D images had a resolution of 182 (H) × 140 (V) pixels and a viewing angle of 24.5°.     

A full‐color eyewear display using planar waveguides with reflection volume holograms

Abstract— A full‐color eyewear display with over 85% see‐through transmittance with a 16° horizontal field of view was developed. Very low color crosstalk, less than 0.008 Δu′v′ uniformity, and 120% NTSC color gamut were achieved. Waveguides with two in‐ and out‐coupling reflection volume hologram elements enabled a simple configuration that has an optical engine beside the user's temples. The reflection volume hologram elements used on the waveguides realized a small thickness of 1.4 mm for each waveguide, and an out‐coupling reflection volume hologram used as an optical combiner contributed a high see‐through transmittance of 85% due to its wavelength selectivity. However, there are technical challenges in achieving a reasonable screen size and quality color images with optics that utilize holographic waveguides because holograms have large chromatic dispersions compared to conventional optical elements such as lenses and mirrors. Approaches to overcome these issues are described.     

Invited Paper: Super Hi‐Vision projection display for next‐generation TV

Abstract— For future broadcasting, NHK is studying new video services offering very‐high‐picture quality achieved through Super Hi‐Vision. Toward that aim, a projection display that has a resolution equivalent to 7680 × 4320 pixels by using four 4096 × 2160 D‐ILA? panels has been developed. The display requires precise convergence adjustment because it consists of two projection units, so an automatic adjustment system was developed. Although the pixel number of the digital camera used is less than that of the display, a 0.2‐pixel accuracy was obtained. This report introduces theaters that use this display as an example of applying the Super Hi‐Vision video system.     

Simple pixel circuits for high resolution and high image quality organic light emitting diode‐on‐silicon microdisplays with wide data voltage range

Two simple pixel circuits are proposed for high resolution and high image quality organic light‐emitting diode‐on‐silicon microdisplays. The proposed pixel circuits achieve high resolution due to simple pixel structure comprising three n‐type MOSFETs and one storage capacitor, which are integrated into a unit subpixel area of 3 × 9 µm² using a 90 nm CMOS process. The proposed pixel circuits improve image quality by compensating for the threshold voltage variation of the driving transistors and extending the data voltage range. To verify the performance of the proposed pixel circuits, the emission currents of 24 pixel circuits are measured. The measured emission current deviation error of the proposed pixel circuits A and B ranges from ?2.59% to +2.78%, and from ?1.86% to +1.84%, respectively, which are improved from the emission current deviation error of the conventional current‐source type pixel circuit when the threshold voltage variation is not compensated for, which ranges from ?14.87% to +14.67%. In addition, the data voltage ranges of the proposed pixel circuits A and B are 1.193 V and 1.792 V, respectively, which are 2.38 and 3.57 times wider than the data voltage range of the conventional current‐source type pixel circuit of 0.501 V.     

Flexible AMOLED displays on stainless‐steel foil

Abstract— The world's thinnest flexible full‐color 5.6‐in. active‐matrix organic‐light‐emitting‐diode (AMOLED) display with a top‐emission mode on stainless‐steel foil was demonstrated. The stress in the stainless‐steel foil during the thermal process was investigated to minimize substrate bending. The p‐channel poly‐Si TFTs on stainless‐steel foil exhibited a field‐effectmobility of 71.2 cm²/N‐sec, threshold voltage of ?2.7 V, off current of 6.7 × 10¹³ A/μm, and a subthreshold slope of 0.63 V/dec. These TFT performances made it possible to integrate a scan driver circuit on the panel. A top‐emission EL structure was used as the display element, and thin‐film encapsulation was performed to realize a thin and flexible display. The full‐color flexible AMOLED display on stainless‐steel foil is promising for mobile applications because of its thin, light, rugged, and flexible properties.     

High‐resolution and high‐brightness full‐colour “Silicon Display” for augmented and mixed reality

High‐brightness micro‐LED display bonded onto silicon backplane has been successfully demonstrated. The 0.38‐inch full‐colour active matrix LED microdisplay system consists of 352 × 198 pixels. Each pixel is 24 μm square composed of red, green, and blue (RGB) subpixels corresponding to a pixel resolution of 1053 ppi. Quantum‐dot materials are formed on III‐nitride blue micro‐LED array to convert blue light into red and green for full‐colour operation. We have confirmed that this microdisplay, which we call “Silicon Display” has wide colour gamut exceeding 120% of sRGB. We describe the advantage of this colour‐converting approach for the full‐colour micro‐LEDs. Progress toward higher resolution is also described. Brightness of more than 30 000 cd/m² has been confirmed at a driving current density of 4 A/cm² for 3000 ppi blue monochrome micro‐LED prepared for full‐colour Silicon Display. We believe our “Silicon Display” is ideally suited for near‐to‐eye displays for augmented and mixed reality.     

Avoiding on‐screen metamerism in N‐primary displays

Abstract— The present paper describes a method for using more than three primaries in an additive‐primary display. The method ensures that each tristimulus specification can be produced in no more than one way, even if a non‐singular filter (i.e., one that does not reduce the dimensionality of color‐matching space) is interposed between the screen and the viewer. Starting with N primaries, the method uses only three at a time, but these may be composites — fixed linear combinations of the original N. As further insurance against on‐screen metamerism, a criterion on the primary spectra, based on the Binet‐Cauchy theorem, ensures that a triad of primaries keeps its right/left‐handed chromaticity ordering when a filter is interposed.