KSF Phosphor: A Decade of Dominance for Wide Color Gamut Displays

Latest Advances in Narrow‐Band Phosphors and Their Role in Color Management

In recent years quantum dots (QDs) emerge as a powerful building block for liquid‐crystal display (LCD) technology, and they are successfully used in the form of color enhancement films. However, their transition toward efficient and wide color gamut LEDs for backlighting remain as an important challenge, which can decrease the required amount of QDs per TV for orders of magnitude. Herein, QD‐based white LEDs are reported that can simultaneously operate with a high external quantum efficiency (EQE) of 39.8% and a wide NTSC color gamut coverage of 133.3%. For red‐emitting spectral range, giant CdSe/CdS core/shell QDs are synthesized via hot injection method, and it is observed that 20 monolayers of CdS shell can lead to a near‐unity photoluminescence quantum yield (PLQY) of 98%. In addition, green‐emitting CdZnSeS/ZnS alloyed core/shell QDs show a PLQY of 97% with a narrow full width at half maximum (FWHM) of 20 nm. To maintain the optical properties of QDs in device architecture, QDs are injected in liquid matrix on blue LED chips and used as the backlighting source for LCD TV that lead to bright and vivid colored images. QD‐based white LEDs with high efficiency and wide color gamut have significant potential for next‐generation display technology.

Effect of silica encapsulation on the stability and photoluminescence emission of FAxCs1-xPbX3 quantum dots for white mini light emitting diodes

A dual-panel liquid crystal displays (LCD) that can switch between wide colour gamut (WCG) mode and high luminance (HL) mode is proposed. Expect the main panel for display, an additional sub-panel is used as the mode switch. In the WCG mode, the colour gamut of dual-panel LCD is 16%NTSC wider than the regular WCG LCD. In the HL mode, the luminance of dual-panel LCD is 21.6% higher than the regular WCG LCD. The other parameters, including driving voltage, response time and viewing angle are also investigated. This dual-panel LCD shows better colour and luminance performance than regular LCD.

A standard color gamut can be obtained with CMYK samples that are printed with an offset printing system according to the ISO 12647-2:2013. It is possible to enhance or widen the color gamut during the printing process by interfering with the density and dot gain characteristics. Printing with a wider color gamut provides a more vivid area and more depth in color. In this study, print trials were conducted at first with standard values (density, dot gain and such). Then another trial was conducted by changing the density values respectively during the trial. Ink density values for all colors were decreased from the standard value as -0.15D, -0.30D and then increased as +0.15D, +0.30D. Color gamuts of the trials were calculated and compared at the end. It is found that ink density values directly affect color gamut in offset printing. It is also found that the color gamut decreases equally when ink density values decrease and vice versa. However, some printing problems occurred with high density values even though it gave an expanded color.

The authors have developed two types of wide color gamut monitor and compared their characteristics. This paper provides an introduction to the color reproduction and standard color space of displays as well as an interpretation of the two types of typical wide color gamut displays that are currently under development. The CRT displays with a wide color gamut are rich in gray levels and viewing angle characteristics while the LCD displays with a LED backlight style have high brightness performance and a broad color gamut. Both types of display support the color gamut of Adobe RGB, enabling compatibility with the extended color space, now beginning to be disseminated, and they also provide a breakthrough for industries that need color management.

We have developed a 17‐inch laser backlight in‐plane switching liquid crystal display satisfying the main BT.2020 specifications, which are 8K, 120‐Hz driving, and a BT.2020 wide color gamut. The color gamut of the developed in‐plane switching liquid crystal display covers 98% of the BT.2020 wide color gamut, thanks to a laser backlight and appropriate color filters. The liquid crystal response time of 5 ms, which is sufficient for 120‐Hz driving, is achieved by adapting a faster in‐plane switching liquid crystal display, namely, the short‐range lurch control in‐plane switching liquid crystal display.

Abstract— The demand for projectors with high brightness and wide color gamut has been increasing; however, UHP lamp projectors cannot deliver those two qualities efficiently and simultaneously because of its color‐separation system. The newly developed projection system — “Color‐Tuning Projection System” — realizes the adaptive combination of high brightness and wide color gamut with one projector. This projector features a fourth liquid‐crystal panel — “Color Tuner” — with a 3LCD optical engine, which controls yellow light separately from the RGB light of a UHP lamp. This color‐tuner‐based optical engine — “Color‐Tuning Optical Engine” — and a new color‐conversion signal‐processing algorithm — “Adaptive Color Conversion Algorithm” — controls the yellow‐light volume and corrects color‐shifted pixels according to the brightness and chromaticity analysis of the input image, key technologies of the Color‐Tuning Projection System. This additional panel system enables the projector to ach ieve up to 115% higher brightness and 120% wider color gamut according to the input image. This paper presents an innovative design concept, a novel technology regarding brightness and a color‐gamut conversion projection system, and the characteristics of the prototype.

Organic light emitting diodes (OLEDs) are considered to be among the best flat panel display technologies owing to their wide viewing angles, high-speed response, high resolution, and simple structure. OLEDs exhibit a wide color gamut exceeding 100 % of the national television system committee (NTSC) sRGB gamut ratio. However, most movies and images are made to comply with standard specifications of the sRGB color gamut. If a sRGB image is displayed on a wide gamut display, the color tone will be distorted. In this paper, we propose a color gamut mapping system using the CIE-1931 XYZ color space for digital image processing. White point and RGB primaries correction provide color gamut correction for different measurement devices of the color gamut. An evaluation using images shows that the proposed system can convert a wide color gamut such as that of OLEDs to the color gamut of the user’s choice without color distortion.

In order to achieve the standard red, green, and blue (sRGB) standard color gamut in color liquid crystal display and improve the image quality, the impact of the backlight and color filter spectrum on module's chroma was simulated and analyzed. The color gamut was enhanced by adjusting and optimizing the two parts of spectrums of LED backlight and color filter and by using red and green phosphor LED backlight to match the new color filter with an appropriate thickness. Experimental results show that: When the thickness of color filter is 2.2 µm, National Television System Committee color gamut increases from 65.3% to 74.9%, and sRGB matching rate enhances from 83.2% to 100%, achieving a full coverage of the sRGB standard color gamut, the transmittance of white light reaches 28.1%. Also, it is verified that shifting the peak position of the backlight and color filter spectrum to purification direction, as well as narrowing its half‐width can upgrade the color gamut. Meanwhile, the thicker the thickness of color filter is, the wider color gamut it has, based on the same pigment material.

Recently, upconversion nanophosphor (UCNP)‐based displays have received increased attention, with emerging reports on transparent displays utilizing multicolor upconversion luminescence from single UCNPs. For these display devices, color reproducibility is one of the most essential properties and the multicolor‐emitting UCNPs are required to exhibit a wide color gamut (WCG) for enhanced color reproducibility. However, achieving both high brightness and WCG properties simultaneously remains challenging for multicolor‐emitting single UCNPs. Here, bright red/green/blue (RGB) orthogonal luminescent core@sextuple‐shell (C@6S) UCNPs showing a WCG under 800, 980, and 1532 nm near‐infrared (NIR) light is reported. Luminescent properties of various C@6S UCNPs with 6 distinct R‐G‐B configurations are investigated and a green‐emitting core coated with a red‐emitting inner shell and a blue‐emitting outer shell satisfied high brightness and WCG properties. The green‐emitting core‐based C@6S UCNPs showed multicolor tunability with high brightness and the widest color gamut value of 94.2% of the National Television System Committee color space among RGB‐emitting core@multishell UCNPs. Furthermore, potential full‐color displays utilizing the transparent C@6S UCNP‐polydimethylsiloxane composite and NIR light sources are demonstrated. These findings provide the criteria for synthesizing the RGB‐emitting single UCNPs exhibiting high brightness and a WCG and would be beneficial for the realization of true 3D full‐color displays.

We have investigated the image quality attribute due to the wide color gamut by comparing it with the conventional sRGB color gamut. The results from the comparison between the two displays showed that 93% of the selected images appeared to have more 'Sharpness' when displayed on the wide gamut display. Previous studies on wide gamut displays were mainly focused on how natural it looked with the color gamut covering the real object color gamut. However we found that the prior image quality attribute for wider color gamut is sharpness caused by chroma contrast. Therefore Sharpness is the main image quality attribute for wide color gamut displays and could be the main factor in image quality improvement.

The International Telecommunication Union Radiocommunication Sector (ITU-R) Recommendation BT.2020 was standardized for ultra-high definition television (UHDTV). The BT.2020 specifications are 8K resolutions, a wide color gamut, and 120-Hz driving. The BT.2020 color gamut is defined from the three primary monochrome colors. Therefore, changing the light source of the backlight from conventional light-emitting diodes (LEDs) to lasers is necessary. We succeeded in prototyping a 17-inch 8K liquid crystal display (LCD) that satisfies the BT.2020 specifications. The pixel density of the 17-inch 8K display is 510 ppi, and the color gamut covers 97% of BT.2020. The liquid crystal response time is 5 ms, which is sufficient for the 120-Hz driving. To achieve the above-mentioned specifications, we developed the following technologies. To expand the color gamut, an RGB laser backlight was used. A backlight with conventional LEDs as light sources only covered 52% of BT.2020. To reduce response time, we applied a faster in-plane switching LCD (IPS-LCD) named short-range lurch control (SLC) IPS-LCD. We succeeded in realizing a blur-free display using the SLC IPS.

One use case that the scalable extension (SHVC) of the state-of-the-art High Efficiency Video Coding (HEVC) standard aims for is to support Ultra High Definition (UHD) TV broadcast in a backwards compatible way with the existing High Definition (HD) TV broadcast. However, since UHD content typically has higher bit-depth and wider color gamut in addition to increased spatial resolution, the compression efficiency is highly affected by the inter-layer processing applied on the base layer picture. This paper proposes an improvement for the weighted prediction based color gamut scalability to have a better mapping between the color gamuts of the base and enhancement layers. The proposed method aims at capturing the nonlinear characteristics of the color gamut mapping using a piecewise linear model, whose parameters are signaled through weighted prediction mechanism and multiple inter-layer reference pictures. Compared to other existing methods for color gamut mapping in SHVC, such as the 3D Look Up Table (LUT) method, the proposed weighted prediction based approach is less complex, as it does not require any changes to the decoder. The simulation results show up to 3.8% Bjontegaard delta bitrate gain in luma for all intra and 3.0% for random access configurations compared to the existing weighted prediction based scalability method in SHVC.

Featuring high bandwidth and low latency, the fifth-generation (5G) network can handle Ultra-High Definition (UHD) video services including 4K and 8K with High Dynamic Range (HDR) and Wide Color Gamut (WCG). In order to ensure high quality for consumers, the parameters of UHD video contents such as resolution, bit depth, frame rate, color gamut and etc. are usually signaled during the whole workflow to keep quality consistency and interoperability. When the signaling is unavailable or unreliable, the end users are likely to obtain unpleasant quality. In this paper, we propose a novel framework for CNN based luminance and color characteristic detection to detect the actual UHD video parameters directly from pixels rather than signaled parameters, which consists of two image classification networks to capture high-level video feature representation. By utilizing Multi-Class Image Reference (MCIR) and Local Feature Extraction and Fusing (LFEF) sub-networks, our scheme performs well on color gamut and dynamic range detection. Experiments on practical video contents show that our system can achieve accuracy of 99.4% and 94.9% on color gamut and dynamic range classification separately.