Multi‐primary‐color LCD: Its characteristics and extended applications

Abstract— The development of multi‐primary‐color (MPC) display systems is one of the big paradigm shifts in recent display technologies and induces new potentials of display devices. The development of MPC display systems for different goals is briefly reviewed. Especially, by employing MPC systems, it is possible to reproduce the real material colors faithfully and efficiently. For signal processing, MPC systems have a big advantage in the so‐called color‐reproduction redundancy. A number of applications can be derived from this characteristic, such as improving the viewing‐angle dependency issue and power savings. On the other hand, MPC systems have a typical trade‐off versus RGB‐standardized input signals, especially for reproducing bright green. New algorithms to moderate this trade‐off on MPC systems by employing color‐reproduction redundancy are proposed. The goal of our algorithms is to maintain the compatibility with RGB‐based input signals though the initial display design so that the characteristics of MPC systems are not changed or lost. These algorithms indicate that MPC display systems are applicable not only for a specifically limited objective but also for other applications, e.g., TV broadcasting.     

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.     

Color‐breakup evaluation of spatio‐temporal color displays with two‐ and three‐color fields

Abstract— Spatio‐temporal color displays have higher transmission and resolution than conventional LCDs, but suffer from color breakup. In this paper, a 120‐Hz display with two‐color filters and two‐color fields is described and the amount of color breakup is compared with that of a 180‐Hz full‐color‐sequential display with no color filters and three‐color fields. The results indicate that color breakup in a color‐filterless display is annoying, whereas it is just visible in displays with two‐color filters even though the refresh rate is much lower.     

Color displays and flexible displays using quick‐response liquid‐powder technology for electronic paper

Abstract— Color displays and flexible displays that use electronic liquid powder have been developed. Novel types of color displays using either a colored powder or a color filter are discussed. We have also developed a flexible display with low‐cost substrate films with a high‐throughput roll‐to‐roll manufacturing method. These technologies enable a QR‐LPD to be widely used as an electronic‐paper display.     

Flexible active‐matrix OLED displays: Challenges and progress

Abstract— Organic light‐emitting‐device (OLED) devices are very promising candidates for flexible‐display applications because of their organic thin‐film configuration and excellent optical and video performance. Recent progress of flexible‐OLED technologies for high‐performance full‐color active‐matrix OLED (AMOLED) displays will be presented and future challenges will be discussed. Specific focus is placed on technology components, including high‐efficiency phosphorescent OLED technology, substrates and backplanes for flexible displays, transparent compound cathode technology, conformal packaging, and the flexibility testing of these devices. Finally, the latest prototype in collaboration with LG. Phillips LCD, a flexible 4‐in. QVGA full‐color AMOLED built on amorphous‐silicon backplane, will be described.     

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 new field‐sequential‐color LCD without moving‐object color break‐up

Abstract— A new display method for field‐sequential‐color liquid‐crystal displays (FS‐LCDs) that reduces the negative effects of color break‐up associated with moving objects has been developed. The method is called Adjustment of Color Element on the Eyes (ACE), and it relies on the position on the eyes of RGB color sub‐images. It was confirmed that color break‐up also does not occur for peripheral objects when using ACE.     

A fast‐switching OCB‐mode LCD for high‐quality display applications

Abstract— Optically compensated bend (OCB) mode is a promising technology, due to its wide range of viewing angles without gray‐scale inversion or color shift, fast response, high contrast ratio, and wide temperature range. This paper summarizes the fundamental characteristics of OCB mode and discusses the development of field‐sequential‐color displays and 3‐D displays for future high‐quality display applications.     

Color‐conversion method for a multi‐primary display to reduce power consumption and conversion time

Abstract— A color‐conversion method for a light‐emitting multi‐primary‐color display is proposed. While amulti‐primary‐color display uses four or more primary colors to reproduce a wide color gamut, multiple sets of primary‐color signals are needed to reproduce one color. Therefore, linear programming, which results in low power consumption, was adopted to uniquely determine the set of primary‐color signals. Although a highly accurate color conversion was achieved by using linear programming with low power consumption, it requires a very long time to convert colors of high‐resolution images. Therefore, by categorizing the color conversion of linear programming as a classification problem, colors are converted by using the decision‐tree method, which is a classification method. As a result, color conversion with high accuracy, low power consumption, and short conversion time was achieved.     

A novel spectrum‐sequential display design with a wide color gamut and reduced color breakup

Abstract— The advantage of RGB color‐sequential displays is that they have no color filters, but the disadvantage is that they need to run at high refresh rates (> >180 Hz) to prevent flicker and color breakup. An alternative color‐sequential display, which can operate at relatively low refresh rates (～ 100 Hz) without disturbing color breakup or flicker, has been developed. The display has two color filters per pixel (cyan and magenta) on the LCD panel and the backlight can generate two types of spectra (blue‐green and green‐red), which results in a wide gamut four‐primary display, effectively. One part of the paper describes the color reproduction, including color‐filter design, gamut mapping, and multi‐primary conversion. The other part deals with the reduced perception of color breakup on the novel spectrum‐sequential display compared to conventional color‐sequential displays.     

Analysis of color volume of multi‐chromatic displays using gamut rings

There are claims that multi‐chromatic displays can achieve a wider color gamut by the use of additional highly saturated secondary color channels. However, there are other claims that these displays lose lightness and/or color saturation at brighter levels. These apparently divergent views have led to some controversy in the display industry and at standard setting organizations. This study examines the color gamut volume for a variety of simulated and measured multi‐chromatic (sometimes incorrectly referred to as “multi‐primary”) displays using combinations of white and/or secondary color channels, such as cyan, magenta, and yellow. Furthermore, a two‐dimensional gamut representation, referred to as “gamut rings,” is introduced to illustrate that the addition of nonprimary optical color channels to a trichromatic (RGB) display can result in a significant decrease in the chroma at higher lightness levels. The additional saturated color channels can increase the gamut volume only around their hues at darker levels. The results also confirm the validity of comparing the color light output and white light output for revealing the design trade‐offs between the high‐peak white and the color‐image brightness for multi‐chromatic displays.     

A field‐sequential‐color display with a local‐primary‐desaturation backlight scheme

Abstract— Field‐sequential‐color technology eliminates the need for color filters in liquid‐crystal displays (LCDs) and results in significant power savings and higher resolution. But the LCD suffers from color breakup, which degrades image quality and limits practical applications. By controlling the backlight temporally and spatially, a so‐called local‐primary‐desaturation (LPD) backlight scheme was developed and implemented in a 180‐Hz optically compensated bend (OCB) mode LCD equipped with a backlight consisting of a matrix of light‐emitting diodes (LEDs). It restores image quality by suppressing color breakup and saves power because it has no color filter and uses local dimming. A perceptual experiment was implemented for verification, and the results showed that a field‐sequential‐color display with a local‐primary‐desaturation backlight reduced the color breakup from very annoying to not annoying and even invisible.     

High‐performance OCB‐mode field‐sequential‐color LCD

Abstract— Optically compensated bend (OCB) mode is a promising technology for future high‐quality display devices due to its wide viewing angle without gray‐scale inversion and color shift, fast response time, high contrast ratio, and wide temperature range. This paper summarizes the developments of the OCB mode and the optical performance of OCB‐mode field‐sequential‐color LCD.     

Efficient and simple methods for display tone‐response characterization

Abstract— Color characterization is an important step towards achieving accurate color on displays. The characterization process typically uses colorimetric or spectrophotometric instruments to measure displayed colors, and relates these to digital values driving the device. Such measurements can be impractical for consumer applications. This paper presents two techniques for characterizing a display's tone response with no colorimetric or spectrophotometric measurements. The first is a visual technique applicable to devices that exhibit a “gamma” response, such as the cathode‐ray tube. The novelty lies in the replacement of the standard luminance matching with gray‐balancing for the blue channel. This approach substantially reduces observer variation in the gamma estimates for the blue channel. The second technique is applicable for the more general case of devices that do not conform to the gamma response, such as LCDs. The visual task is augmented with a consumer digital camera used as a color‐capture device. The camera tone response is first characterized via a visual task. The characterized camera is then treated as a colorimeter and used to generate a tone‐response characterization for the display. Experiments conducted on projection displays demonstrate that satisfactory quality can be achieved while eliminating the need for costly and tedious measurement.     

Passive‐matrix‐driven field‐sequential‐color displays

Abstract— Passive‐matrix‐driven field‐sequential‐color (FSC) displays were successfully fabricated. It makes use of a new multiplex driving scheme that does not depend on voltage averaging. Instead, a transient response of the liquid crystal is employed. An addressing and response time of less than 70 μsec and 2.0 msec, respectively, are used. Scanning time compensation is also introduced to improve the brightness uniformity of the display.     

Large‐area FEDs with carbon‐nanotube field emitter

Abstract— Application of carbon nanotubes (CNTs) as field emitters for large‐area FED panels is described. In 1998, we presented the first experimental devices: light‐source tubes for outdoor large‐area displays and a diode‐type flat‐panel display, both with screen‐printed CNT cathodes. The fisrt practical high‐luminance color CNT‐FED panel was built in 1999. It employed the new triode‐structure panel was x‐y addressable. The CNT‐FED structure was further optimized for large‐area display panels by improving the luminous uniformity. This paper also describes the design and performance of a new, experimental, 40‐in.‐diagonal panel, which showed that the CNT‐FED technology is suitable for use in large‐area displays.     

Relationship between mode‐boundary from surface color to fluorescent appearance and preferred gamut on wide‐gamut displays

Abstract— Color‐gamut design is a major concern in wide‐gamut displays. To determine a preferred gamut for displaying object color in natural scenes on a wide‐gamut display, subjective evaluations were conducted to investigate the preferred color and acceptable limit. Then, simple synthesized images were used to determine the mode boundary between surface color and fluorescent color appearance. It was found that (1) observers perceived the colors with high saturation and high lightness as fluorescent colors and (2) the fluorescent appearance decreased preference. The color‐mode index (CMI) was defined as an evaluation index of the color‐appearance mode so that the boundary between surface color and fluorescent color appearance was defined as CMI 100. Additionally, it was found that the CMI 100 loci could be interpreted as an optimal color loci. Then, it was clarified that the mode boundary and the preferred gamut were closely related and that the acceptable limit for L* was 1.1 times L* for CMI 100.     

Color reproduction with a various number of sub‐pixels

Monochrome reflective‐type displays are widely used for portable reading applications such as electric papers because this type does not need a back light unit and can be used outdoors for a long time. Color reflective‐type displays without back light units are desired to expand the market further. The current color reproduction is based on three sub‐pixel red, green and blue (RGB) methods, and when used in reflective type, its luminance is reduced to a third of that of monochrome type. Adding a white sub‐pixel to the current method can improve the luminance, making the sub‐pixel number four. However, in the case of a high resolution display with a four‐sub‐pixel method, the pixel structure is complex, and the luminance improvement may be limited. Instead of increasing the sub‐pixel number, two sub‐pixel methods are investigated. These methods can improve luminance with limited color gamut. The performances are compared with those of other methods quantitatively.     

Advances towards high‐resolution pack‐and‐go displays: A survey

Abstract— Tiled displays provide high resolution and large scale simultaneously. Projectors can project on any available surface. Thus, it is possible to create a large high‐resolution display by simply tiling multiple projectors on any available regular surface. The tremendous advancement in projection technology has made projectors portable and affordable. One can envision displays made of multiple such projectors that can be packed in one's car trunk, carried from one location to another, deployed at each location easily to create a seamless high‐resolution display, and, finally, dismantled in minutes to be taken to the next location — essentially a pack‐and‐go display. Several challenges must be overcome in order to realize such pack‐and‐go displays. These include allowing for imperfect uncalibrated devices, uneven non‐diffused display surfaces, and a layman user via complete automation in deployment that requires no user invention. We described the advances we have made in addressing these challenges for the most common case of planar display surfaces. First, we present a technique to allow imperfect projectors. Next, we present a technique to allow a photometrically uncalibrated camera. Finally, we present a novel distributed architecture that renders critical display capabilities such as self‐calibration, scalability, and reconfigurability without any user intervention. These advances are important milestones towards the development of easy‐to‐use multi‐projector displays that can be deployed anywhere and by anyone.     

A4‐sized flexible ferroelectric liquid‐crystal displays with micro color filters

Abstract— We demonstrated an A4‐paper‐sized flexible ferroelectric liquid‐crystal (FLC) color displays fabricated by using a new plastic‐substrate‐based process which was developed for large‐sized devices. Finely patterned color filters and ITO electrodes were formed on a plastic substrate by a transfer method to avoid surface roughness and thermal distortion of the substrate, which induce disordering of the FLC molecular alignment. The thickness of an FLC/monomer solution sandwiched by two plastic‐film substrates was well controlled over a large area by using flexographic printing and lamination techniques. Molecular‐aligned polymer walls and fibers were formed in the FLC by a two‐step photopolymerization‐induced phase‐separation method using UV‐light irradiation. A fabricated A4‐sized flexible‐sheet display for color‐segment driving was able to exhibit color images even when it was bent.