Large Color Gamut Research Articles

Verification of the CAM15u colour appearance model and the QUGR glare model

A psychophysical experiment was carried out to evaluate the glare, brightness, whiteness and hue composition of a glare source made by a multiple-channel LED lighting system. About 80 stimuli were produced to cover a large colour gamut at two luminance levels, 280 and 2400 cd/m2, respectively. The results were used to verify the earlier CAM15u colour appearance model and the QUGR glare model. A revised model, CAM15uz, is refined from CAM15u by adding an effect of hue to the prediction of brightness caused by the Helmholtz–Kohlrausch effect. In addition, a new hue composition scale is established.

K_2SiF_6:Mn^4+ as a red phosphor for displays and warm-white LEDs: a review of properties and perspectives

Phosphor-converted white light-emitting diodes (pc-WLEDs) are energy efficient and environmentally friendly light sources with a long lifetime, applicable in both display backlights and general lighting. Adding red-emitting phosphors improves the color quality of white LEDs compared to the prototype combination of a blue LED and the yellow Y3Al5O12:Ce3+. Efficient narrow-band red-emitting phosphors like K2SiF6:Mn4+ can meet the market’s needs. This review recapitulates research since 2008 on K2SiF6:Mn4+ as the first and most discussed fluoride phosphor. The limited nephelauxetic effect, typical for fluorides, allows for the tuning of the Mn4+ emission in the red part of the spectrum below 650 nm. This is reflected in the spectroscopic parameters of the crystal field theory. Synthesis methods are described, showing the evolution from etching Si wafers to solution synthesis resulting in consistent luminescent and thermal properties. Though important for applications, long-term stability is often neglected, although (in)organic coatings improving stability emerge. This leads not only to warm-white LEDs with high efficacies and good color rendering, but also to efficient displays with a large color gamut.

PH-induced azo-keto and azo-enol tautomerism for 6-(3-methoxypropylamino)pyridin-2-one based thiophene azo dyes

The synthetic strategy of combining functional group transformation (FGT) and post-modification (PM) is proposed to prepare two new types of 2-amino-3-cyano-4-chloro-5-formylthiophene based heterocyclic azo dyes with mono and double 3-methoxypropan-1-amine substituted pyridine components, where the terminal aldehyde radical of the 2-formylthiophene moiety is extended into imine, acetal or α,β-unsaturated cyanoacetic ester group. The evaluation of pH stability of the mono FGT products indicates that the basic stability is depended upon the π-conjugated system of the diazo components by comparing our synthesized thiophene and azobenzene based dyes, in which better electron delocalization may facilitate the proton transfer within molecule resulting in poor stability towards base. Furthermore, the intra-ring azo-keto ⇌ azo-enol tautomerism in the coupling components is suggested to explain the appearance of five isoabsorptive points in their pH-titration experiments. In contrast, all the N2,N6-bis(3-methoxypropyl)pyridine-2,6-diamine based azo dyes exhibit extremely high pH stability no matter what diazo components are used, because no proton accepting sites are present after the double FGT. It is also found that the synthesized thiophene heterocyclic dyes exhibit a large color gamut after PM. For example, the maximum absorption wavelength (λmax) is significantly red-shifted from 496 nm in the acetal compound to 590 nm in the cyanoacetic ester terminated dye.

Geometric and Photometric Consistency in a Mixed Video and Galvanoscopic Scanning Laser Projection Mapping System.

We present a geometric calibration method to accurately register a galvanoscopic scanning laser projection system (GLP) based on 2D vector input data onto an arbitrarily complex 3D-shaped projection surface. This method allows for accurate merging of 3D vertex data displayed on the laser projector with geometrically calibrated standard rasterization-based video projectors that are registered to the same geometry. Because laser projectors send out a laser light beam via galvanoscopic mirrors, a standard pinhole model calibration procedure that is normally used for pixel raster displays projecting structured light patterns, such as Gray codes, cannot be carried out directly with sufficient accuracy as the rays do not converge into a single point. To overcome the complications of accurately registering the GLP while still enabling a treatment equivalent to a standard pinhole device, an adapted version is applied to enable straightforward content generation. Besides the geometrical calibration, we also present a photometric calibration to unify the color appearance of GLPs and standard video projectors maximizing the advantages of the large color gamut of the GLP and optimizing its color appearance to smoothly fade into the significantly smaller gamut of the video projector. The proposed algorithms were evaluated on a prototypical mixed video projector and GLP projection mapping setup.

55‐3: Invited Paper: Delivering Content for HDR

In 2016, every major manufacturer revealed High Dynamic Range (HDR)‐compatible TVs. The technology promises a major improvement of the quality of images delivered to consumers. The goal of HDR technology is not to simply increase the contrast of existing images but to display more tonal details in the shadows and highlights. In combination with higher brightness levels and a larger color gamut, more realistic and captivating images are created.Current industry standards demand a contrast of 20000:1 or better for HDR displays opposed to about 1000:1 for traditional displays. This raises the requirements for the dynamic range of cameras used to produce HDR content. The ARRI ALEXA camera, released in 2010, is based on a sensor that has a dynamic range (ratio of full‐well capacity to read‐out noise) of approx. 30000:1. This very high range is achieved by a combination of a dual‐gain pixel architecture and an elaborate sensor calibration procedure. Without effective correction of nonuniformities, the usable dynamic range of the complete sensor may be less than the dynamic range of its single pixels. While existing workflows in motion‐picture and digital video are suitable to produce HDR content there are no well‐established procedures for the evaluation of the performance of digital cameras. An outline of such a procedure is proposed.

Going beyond the limit of an LCD\u2019s color gamut

In this study, we analyze how a backlight’s peak wavelength, full-width at half-maximum (FWHM), and color filters affect the color gamut of a liquid crystal display (LCD) device and establish a theoretical limit, even if the FWHM approaches 1 nm. To overcome this limit, we propose a new backlight system incorporating a functional reflective polarizer and a patterned half-wave plate to decouple the polarization states of the blue light and the green/red lights. As a result, the crosstalk between three primary colors is greatly suppressed, and the color gamut is significantly widened. In the experiment, we prepare a white-light source using a blue light-emitting diode (LED) to pump green perovskite polymer film and red quantum dots and demonstrate an exceedingly large color gamut (95.8% Rec. 2020 in Commission internationale de l'éclairage (CIE) 1931 color space and 97.3% Rec. 2020 in CIE 1976 color space) with commercial high-efficiency color filters. These results are beyond the color gamut limit achievable by a conventional LCD. Our design works equally well for other light sources, such as a 2-phosphor-converted white LED.

Highly efficient omnidirectional structural color tuning method based on dielectric-metal-dielectric structure.

A novel and convenient scheme is proposed to achieve angle insensitive color filtering across a large color gamut by simply altering the thickness of the dielectric layer of a dielectric-metal-dielectric grating structure. The plasmonic filter presents a great feature of angle resolved spectrum response up to 60° and is independent of the azimuthal angle and the polarization state as well so as to construct an omnidirectional filter for practical applications. The color tuning feature of the proposed filter with varied dielectric thickness is attributed to the modulation of the condition for the localized surface plasmon resonance, which bears responsibility for the omnidirectional property of this plasmonic filter. This color-tuning method with a single mold size required can have wide applications in fields of display, colorful decoration, printing, and so forth.

Consequences of ET and MMCT on Luminescence of Ce(3+)-, Eu(3+)-, and Tb(3+)-doped LiYSiO4.

Ce(3+), Eu(3+), and Tb(3+) singly doped, Ce(3+)-Tb(3+), Tb(3+)-Eu(3+), and Ce(3+)-Eu(3+) doubly doped, as well as Ce(3+)-Tb(3+)-Eu(3+) triply doped LiYSiO4 phosphors were prepared by a high-temperature solid-state reaction technique. Rietveld refinement was performed to determine the structure of host compound. The cross-relaxation (CR) of Tb(3+) is quantitatively analyzed with the Inokuti-Hirayama model of energy transfer (ET), and the site occupancy is confirmed by emission spectra of Eu(3+). ET and metal-metal charge transfer (MMCT) are systematically investigated in Ce(3+)-Tb(3+), Tb(3+)-Eu(3+), and Ce(3+)-Eu(3+) doubly doped systems. The combined effects of ET and MMCT on luminescence and emission color of Ce(3+)-Tb(3+)-Eu(3+) triply doped samples are discussed in detail, showing that the photoluminescence emission is tunable in a large color gamut.

Subtractive Color Filters Based on a Silicon-Aluminum Hybrid-Nanodisk Metasurface Enabling Enhanced Color Purity.

Highly efficient subtractive tri-color filters of cyan, magenta, and yellow with enhanced color purity and robustness have been proposed and realized, by exploiting a silicon-aluminum (Si-Al) hybrid-nanodisk (ND) metasurface atop a Si substrate. The aspect ratio of the Si-Al hybrid ND is much lower than that of the conventional Si nanowire, which is disadvantageous due to its fragility and low color purity. In response to incident light impinging upon the metasurface, the hybrid-NDs individually play the role in exciting a magnetic dipole (MD) resonance through the mediation of Mie-scattering between the hybrid ND and air. The light stored in the resonance is coupled to the substrate, giving rise to a suppressed reflection. By virtue of the top Al ND, the excited MD resonance is strongly confined by the Si ND. As a consequence, a near-zero resonant dip that exhibits high off-resonance reflection and narrow bandwidth is produced for embodying highly efficient tri-color filters with enhanced color purity. The spectral position can be tuned by a simple adjustment of the hybrid-ND diameter. A full-color palette was successfully created with a high color purity and large color gamut. The proposed devices may be applied for photorealistic high-resolution color printing and holographic displays.

Large color gamut displays with diffraction gratings.

The ability to display a broad variety of colors has great benefits not only in the context of entertainment but also as a means to streamline design in prototyping and manufacturing processes. Displays that use RGB filters or backlights cannot span all colors that occur in nature. To improve the accuracy of color reproduction, there have been attempts to include additional color primaries in displays. Existing solutions, however, have an impact on cost, scalability, and spatial resolution and are predominantly applicable to projection systems. We propose an approach based on combining diffraction grating extractors and the HANS imaging pipeline initially developed for printing. This combination offers unprecedented potential to attain large color gamuts with the same backlights commercially used today.

Characterising user preference for white LED light sources with CIE colour rendering index combined with a relative gamut area index

The CIE general colour rendering index ( Ra) is still the only widely used and accepted colour fidelity index for characterising white light sources. However, user preference for light sources is not determined by fidelity alone but also by colour saturation. Here, we investigate the impact of fidelity and gamut area on the preference for white light sources in three application areas: fresh food, packaged food and skin tones. Thirty-four participants evaluated the attractiveness of object appearance for seven light sources with Ra values ranging between 70 and 100 and relative gamut area index ( Ga) ranging between 90 and 120. Results show that object appearance was rated as more attractive for light sources with a larger colour gamut, which have Ra values of 80 and lower. In general, light sources with relatively high spectral power in the long wavelength range, enhancing red objects, received the highest preference. We conclude that, next to fidelity, colour saturation makes a significant contribution to the appreciation of a light source. We therefore propose using Ra in conjunction with Ga and a colour rendering graphic for providing a more detailed description of the colour quality of white LED light sources.

Eu2+ → Tb3+ → Eu3+ energy transfer in Ca6La2Na2(PO4)6F2:Eu, Tb phosphors

Eu2+ → Tb3+ → Eu3+ energy transfer exist in CLPF host, and tunable emission with a large color gamut can be obtained under n-UV light excitation.

Highly efficient narrow-band green and red phosphors enabling wider color-gamut LED backlight for more brilliant displays.

In this contribution, we propose to combine both narrow-band green (β-sialon:Eu(2+)) and red (K(2)SiF(6):Mn(4+)) phosphors with a blue InGaN chip to achieve white light-emitting diodes (wLEDs) with a large color gamut and a high efficiency for use as the liquid crystal display (LCD) backlighting. β-sialon:Eu(2+), prepared by a gas-pressure sinteing technique, has a peak emission at 535 nm, a full width at half maximum (FWHM) of 54 nm, and an external quantum efficiency of 54.0% under the 450 nm excitation. K(2)SiF(6):Mn(4+) was synthesized by a twe-step co-precipitation methods, and exhibits a sharp line emission spectrum with the most intensified peak at 631 nm, a FWHM of ~3 nm, and an external quantum efficiency of 54.5%. The prepared three-band wLEDs have a high color temperature of 11,184 - 13,769 K (i.e., 7,828 - 8,611 K for LCD displays), and a luminous efficacy of 91 - 96 lm/W, measured under an applied current of 120 mA. The color gamut defined in the CIE 1931 and CIE 1976 color spaces are 85.5 - 85.9% and 94.3 - 96.2% of the NTSC stanadard, respectively. These optical properties are better than those phosphor-cpnverted wLED backlights using wide-band green or red phosphoprs, suggesting that the two narrow-band phosphors investigated are the most suitable luminescent materials for achieving more bright and vivid displays.

Quantum dots: The ultimate down‐conversion material for LCD displays

AbstractAssuming that large color gamut and therefore better color reproducibility will be a highly desired feature of all displays as we look to the near future, we make the case in this paper that quantum dots (QDs) are currently the down‐conversion technology of choice that will allow liquid crystal display makers to cost‐effectively reach and exceed 100% of the NTSC (National Television Standard Committee) and Adobe RGB color standards while achieving maximum system efficiency. We will discuss in detail the numerous fundamental advantages of QDs over phosphors, along with their scientific origins, and make the case that QDs are the ultimate light generating material for next‐generation displays.

Optimal yarn colour combination for full‐colour fabric design and mixed‐colour chromaticity coordinates based on CIE chromaticity diagram analysis

It is challenging for textile designers to achieve full‐colour effects in woven fabric using a limited set of coloured yarns. The common problems encountered during full‐colour fabric design include an insufficient number of colours and a failure to match the fabric colour with the desired colour. Using the theories of primary colours and optical colour mixing, we examine the mixed‐colour distribution of primary colour yarns on the basis of the CIE 1976 chromaticity diagram (CIE u′v′). In our experiment, dope‐dyed polyester filament yarns were selected as raw materials. Eight kinds of gradually varied weave structures and four types of primary colour combination were adopted in order to make different types of full‐colour fabric colour chart. Spectrophotometer and DigiEye colour measurement systems were selected to measure the reflectance and colour value of the fabric samples. By comparing the colour distribution of mixed fabrics in the CIE u′v′ diagram, the relationship between the primary colour combinations and the colour distribution of mixed fabrics is discussed. Of RGB, CMY, NCS, and RGBCMY combinations, only RGBCMY resulted in a relatively complete and large colour gamut. Moreover, the colour positions of mixed fabrics in the CIE u′v′ diagram were almost all distributed on or near the connecting line of the primary colour coordinates. The specific colour position of mixed fabrics in the CIE u′v′ diagram were mainly determined by the proportion of primary colours on the fabric surface. In this way, a new method for computing colour position in the CIE u′v′ diagram is introduced.

Dichroic colored luster of laser-induced silver nanoparticle gratings buried in dense inorganic films

This paper deals with the colorimetric properties of silver nanoparticle gratings buried in a dense titania film that result from a continuous wave laser-induced self-organization process. The samples exhibit shining colors in the direction of the specular reflection, which are very sensitive to polarization. We show that a large color gamut and a tunable dichroism can be reached by varying the exposure conditions. We also discuss the physical meaning of the observed variations in the dichroism. This laser process produces a single pass marking with a micrometer resolution and could be useful for developing innovative solutions in fields like active color displays, security, polarization imaging, or design.

Physicochemical colourants effects on polymeric composites printing toner

Purpose– This paper aims to report on production of the colour digital printing toners cyan, magenta and yellow. Colour digital electrophotographic printing is currently in high demand. The provision of a large colour gamut depends on appropriate selection of precise colourants to produce toner capable of producing a thin layer on paper.Design/methodology/approach– Printing toners were synthesised by the emulsion aggregation method, and then evaluated for chemical constitution and effects of the colourant substituents.Findings– Results demonstrated that increasing the polarity of a pigment produced better dispersion and lower particle size with narrower distribution and even better colour reproduction. While, changing a pigment’s characteristics did not affect the toner shape or its thermal properties.Practical implications– The developed method provides a simple way to synthesise colour printing toner.Social implications– Emulsion aggregation toners provide less hazardous materials during printing.Originality/value– Evaluations of the influence of solid-state parameters and physicochemical properties of the pigments on printing toner characteristics were done for the first time.

Importance of Eco-Friendly OLED Lighting

The importance of artificial light has long been recognized as it extends the day. Copious corporations and academic institutions are investing cosmic treasures in tracking down the advanced artificial lighting applications with a vision towards energy efficient and eco-friendly solid state lighting. In this regard, organic light-emitting diodes (OLEDs) are going to change the human lifestyle, by offering a promising avenue to develop future energy saving solid-state lighting sources because of their intrinsic characteristics such as low driving voltage, high resolution, high brightness, large viewing angle, large color gamut, high contrast, less weight and size, efficiency etc., there by dictating their ability to reach the pinnacle in the field of flat panel displays and solid state lighting sources. With the goal towards future application, many design strategies like synthesis of novel materials, well judged anatomy of device configuration, development of refined and low cost fabrication techniques have been put forward to achieve high efficiency, good color stability and quality lighting. Practical applications, which enrich the ideas of the specialists in this field to develop new routes for future research development of OLEDs are enumerated and illustrated by specific examples. This chapter also integrates the novel approaches for energy efficient and eco-friendly solid state lighting as well as the limitations and global haphazards of currently used lighting systems. The current state of the art, ongoing challenges and future perspectives of this research frontier to reduce the driving voltage, minimization of degradation issues, enhance their life time are illustrated. Review on the status and future outlook of these OLEDs strongly reveals their emergence in the next few years.

19.1: Invited Paper: Illuminating the Value of Larger Color Gamuts for Quantum Dot Displays

AbstractQuantum dot technology offers the promise of efficient and relatively inexpensive liquid crystal displays (LCDs) with large color gamuts (∼115% NTSC u'v'). Now, for the first time, a variety of high color performance devices are on the immediate horizon for applications ranging from 3“ diagonal hand held smart phones to +85” diagonal TVs . While people clearly prefer color displays, the relative value of different color reproduction systems remains an open question. Here we review how quantum dots enable high color performance and some of the advantages of large color gamut displays.

12.1: Invited Paper: Quantum Dots: The Ultimate Down‐Conversion Material for LCD Displays

AbstractAssuming large color gamut and therefore better color reproducibility will be a highly desired feature of all displays as we look to the near future, we make the case in this paper that Quantum Dots (QDs) are currently the down‐conversion technology of choice that will allow liquid crystal display (LCD) makers to cost‐effectively reach and exceed 100% of the NTSC (National Television Standard Committee) standard while achieving maximum system efficiency. We will discuss in detail the numerous fundamental advantages of QDs over phosphors, along with their scientific origins, and make the case that QDs are the ultimate light generating material for next‐generation displays.