Single display gamut size metric

To measure the relative gamut sizes of wide‐gamut displays, it is herein proposed that the CIE 1931 xy chromaticity diagram be used rather than the nominally perceptually uniform CIE 1976 u′v′ chromaticity diagram. High correlations were found between the area‐coverage ratios in the xy diagram and the volume‐coverage ratios in the CIE 1976 L^*a^*b^* color space for major standard wide‐gamut color spaces. It is also demonstrated herein that performing planimetry in the uniform u′v′ diagram does not yield accurate relative display gamut sizes, even though the large sizes obtained using the u′v′ diagram are often reported regardless of the fact that its uniformity is valid only when the luminance factor is constant. The single display gamut size metric using the xy diagram will facilitate the unbiased development of wide‐gamut displays.     

Measuring the color capability of modern display systems

Historically displays used three colorants in an additive system. During that time, the CIE chromaticity diagram adequately illustrated color capability. Modern displays are not constrained by this additive architecture, and the diagram can fail in its purpose. This is demonstrated by analysis and a large number of display measurements. A device‐independent methodology using CIE 1976 L*a*b* color gamut volume is described that provides a robust means to determine the size of the color gamut. This methodology is then extended to the ‘gamut rings’ diagram as a solution for visualizing color capability that directly correlates to color gamut volume. It is further shown how the methodology can be applied to determine the intersection between two gamut volume boundaries.     

Ultrawide color gamut LCD display with CdSe/CdS nanoplatelets

We present a liquid‐crystal display (LCD) backlight made of nanoplatelets (NPLs) for the first time. Owing to the narrow emission linewidth of NPLs (8‐12 nm) and quantum dots (QDs), the spectrum exhibits a wide color gamut display with a 139.9% color gamut of National Television System Committee (NTSC) 1953 standard and 104.5% Rec.2020 (ITU‐R Recommendation BT.2020), realizing a truly ultrawide color gamut LCD display.     

Detection and correction of purple fringing using color desaturation in the xy chromaticity diagram and the gradient information

This paper proposes a method to detect and correct purple fringing, which is one of color artifacts due to characteristics of charge coupled device sensors in a digital camera. The proposed method consists of two steps: detection and correction of purple fringing. In the first step, we detect the purple fringed regions that satisfy specific properties: image regions with large gradient magnitudes and with the chromaticity values within the purple color range set in the CIE xy chromaticity diagram. In the second step, color of the purple fringed regions is corrected in the CIE xy chromaticity diagram by color desaturation of the detected pixels. The proposed method is able to detect purple fringe artifacts more precisely and correct them more naturally than existing methods. It can be used as a post processing in a digital camera.     

Effects of display properties on perceived color‐gamut volume and preference

Abstract— The effect of varying the color gamut of an extended‐gamut LCD on color appearance and preference was measured psychometrically in two experiments at each of two separate laboratories over a representative set of 10 images each. The first experiment measured the effect of color gamut on appearance, and the effect on the appearance attribute colorfulness was shown to be relatively strong compared with other attributes as the volume of display color gamut is varied. Overall, colorfulness monotonically increased at constant sensitivity as the gamut area in xy chromaticities increased while tending to become less and less sensitive to increasing the gamut volumes in CIELAB and CIECAM02. In the second experiment, the overall preference indicated an optimal color gamut for the display gamut volume even though the results were shown to be highly scene dependent.     

High‐accuracy system for spectral measurement of small‐area‐contrast and low‐light‐level display screens

Abstract— A double‐monochromator spectroradiometer with a photon‐counting detector will be described. The system captures spectroradiometric data with near‐perfect linearity over six decades of intensity and with wavelength uncertainties of under 0.05 nm. It enables accurate measurement of spectral radiance data and small‐area contrast with an uncertainty less than 0.002 in chromaticity (x,y) and 2% in luminance for a typical CRT spectrum.     

White LEDs using the sharp β‐sialon: Eu phosphor and Mn‐doped red phosphor for wide‐color gamut display applications

The sharp β‐sialon (Si_6‐zAl_zO_zN_8‐z : 0 < z < 0.1):Eu green phosphor, combining with a blue LED and CaAlSiN₃:Eu red phosphor, is suitable for the wide‐color gamut white LEDs backlighting system, because of its sharp and asymmetric emission spectrum shape. However, the color gamut and the brightness of the aforementioned display is restricted because of the wide emission band of the CaAlSiN₃:Eu red phosphor. In this work, we used K₂SiF₆:Mn as an alternate red phosphor, which has a sharp emission spectrum. The display with the white LED using sharp β‐sialon:Eu and K₂SiF₆:Mn shows a wide‐color gamut, which covers the hole NTSC triangle. The use of K₂SiF₆:Mn enables to realize not only a wider color gamut but also a higher brightness of displays, compared with the use of CaAlSiN₃:Eu. Furthermore, it is confirmed that the white LED using sharp β‐sialon:Eu and K₂SiF₆:Mn is stable against temperature and also durable under the accelerated drive conditions.     

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.     

Spatially uniform colors for projectors and tiled displays

Abstract— A major issue when setting up multi‐projector tiled displays is the spatial non‐uniformity of the color throughout the display's area. Indeed, the chromatic properties do not only vary between two different projectors, but also between different spatial locations inside the displaying area of one single projector. A new method for calibrating the colors of a tiled display is presented. An iterative algorithm to construct a correction table which makes the luminance uniform over the projected area of one single projector is presented first. This so‐called intra‐projector calibration uses a standard camera as a luminance measuring device and can be processed in parallel for all projectors. Once the color inside each projector is spatially uniform, the set of displayable colors — the color gamut — of each projector is measured. On the basis of these measurements, the goal of the inter‐projector calibration is to find an optimal gamut shared by all the projectors. Finding the optimal color gamut displayable by n projectors in time O(n) is shown, and the color conversion from one specific color gamut to the common global gamut is derived. The method of testing it on a tiled display consisting of 48 projectors with large chrominance shifts was experimentally validated.     

Physical‐based photon mapping for an LED backlight lighting simulator

Abstract— Liquid‐crystal displays (LCDs) have become increasingly popular due to their lower price and larger sizes. In particular, backlights having an RGB LED source have recently attracted attention, because they have a wider color gamut, higher luminance, and lower power consumption. However, even when the backlight area is uniformly covered with light modules based on arrays of individual LEDs, this does not ensure a uniform chromaticity and luminance over the backlight panel, thereby stressing the need for lighting simulation of the backlight. Accordingly, this paper proposes an effective lighting simulator to predict the chromaticity and luminance distribution of an LED backlight panel for an LCD. First, the spectrum‐based photons are all initially generated using a random function with a constraint satisfying the spectral power distribution of the actual LED light sources, while their emitting directions are determined based on a pre‐calculated probability using a random variable angle. The optical characteristics of the inner sheets in the LCD backlight structure are then modeled using the wavelength and incident angle to predict the next direction of each photon based on the reflection and transmittance at an intersection. All the photons that reach the unit area of the outward panel are gathered to shape their spectral power distribution, then converted to CIEXYZ values and multiplied with a color‐matching function. Finally, a realistic image visualization of these CIEXYZ values is achieved through standardized device characterization using the sRGB mode. Experiments confirm that the proposed spectrum‐based photon mapping can effectively predict the chromaticity and luminance distribution of an LED backlight panel, providing a good lighting simulation of an LED backlight before manufacturing the LCD.     

Dynamic adaptation model and equal‐whiteness CCT curves for the choice of display reference white

Abstract— A dynamic adaptation model (DAM), based on the variations in the luminance levels under the same chromaticity viewing conditions and equal‐whiteness correlated‐color‐temperature (CCT) curves (EWCCs) derived by using the proposed DAM, is proposed. The proposed model was obtained by the transformation of the test colors for high luminance into the corresponding colors for low luminance. In the proposed model, the optimal coefficients are obtained from the corresponding color data from Breneman's experiments. From the experimental results, it was confirmed that the chromaticity errors between the predicted colors by the proposed model and the corresponding colors of Breneman's experiments are 0.004 in u′v′ chromaticity coordinates. The prediction performance of the proposed model is excellent because this error is the threshold value that distinguishes two adjacent color patches. Equal‐whiteness CCT curves (EWCs) are also proposed using the proposed DAM. By using the proposed EWCCs, an analysis of the difference between the selected video‐display‐unit reference‐white CCT values can be made. Additionally, the proposed EWCCs can be used as the theoretical standard which determines the reference white of the color video display units.     

Heuristic approach to selecting a color appearance model for hue‐preserved wide‐color gamut mapping

With the advent of wide‐gamut system colorimetry for ultra‐high definition television, the development of a gamut mapping algorithm for wide to standard gamuts is greatly needed. Most gamut mapping techniques have been developed to retain the perceived hues of the source as predicted by a color appearance model. However, some color appearance models erroneously predict the saturated colors, generating a serious hue discontinuity in wide‐color gamut mapping onto the Rec. 709 gamut boundary. This paper presents a heuristic approach to determining whether a color appearance model may create such artifacts when used in hue‐preserved gamut mapping algorithms.     

High efficiency and ultra‐wide color gamut quantum dot LEDs for next generation displays

Colloidal quantum dot‐based hybrid light‐emitting diodes (QLEDs) have been demonstrated that exhibit quantum efficiencies (EQEs) >10% for all three fundamental colors red, green, and blue (21% EQE, 82 cd/A for green). This is the first report of a green QLED with EQE >20% and current efficiency >80 cd/A. The devices have the longest lifetimes reported in the literature (280k hrs) and extremely well‐tuned color fidelity. The narrow QLED emission spectra (full width at half maximum < 30 nm) and well‐controlled peak wavelengths generate a color gamut covering >170% of the National Television System Committee (NTSC) 1987 color space and ~90% of the Rec. 2020 color space. This color gamut is larger than that of OLED televisions in mass production and is the largest of all QLEDs reported. Additionally, these devices are completely fabricated using solution‐processing techniques. The extremely desirable properties of high efficiency, color tunability/fidelity, long lifetime, and low cost processing from solutions make QLED technology disruptive and will lead to next generation displays.     

A method for selecting display primaries to match a target color gamut

Abstract— A method for selecting primaries of a wide‐gamut display is proposed, in which display color gamut is designed to match a target color gamut in CIELAB color space. A standard deviation of the relative maximum chroma of display and target color gamuts is defined. The selection method optimizes display primaries for the minimum standard deviation so that display and target color gamuts are similar in shape. It is shown that the color gamut of a laser display designed by this method is similar in shape to the theoretical maximum, or optimal, color gamut of objects. It is also shown that the color gamut of an LED display can be designed to include 99.7% of the gamut of Pointer's real‐world surface colors. LED primaries are selected to minimize the standard deviation of the relative maximum chroma of effective display color gamut and a target color gamut which is defined to include Pointer's real‐world surface colors. For both the laser and LED displays, it is necessary to constrain the red‐primary wavelength to avoid excessive optical power for the red primary.     

Screen‐based color vision test for digital quantification of deutan color defects using a color‐calibrated monitor

Display technologies are used in various industries. However, few studies on color vision testing using self‐luminous displays are reported. In this study, a screen‐based color vision test, termed the digital color vision test (DCVT), is developed on a color‐calibrated monitor. A control bar is adjusted by the observer to build just noticeable chromatic difference ellipses in CIE u′v′ chromaticity diagram, which indicate the capabilities of subjects' color visions. Ten color‐normal observers and 13 deutan observers participated in the psychophysical experiments. The observers also performed the other two typical diagnostic tests (D‐15 and anomaloscope). Results from the experiment using the adjustment psychophysical method for digital quantification of deutan color vision defects are presented. It is found that the diagnosis accuracy of the DCVT is approximately equivalent to those of D‐15 and anomaloscope tests.     

Monochromatic LEDs based on perovskite quantum dots: Opportunities and challenges

Perovskite quantum dots (QDs) are emerging as one of the most promising candidates for the monochromatic light‐emitting diodes (LEDs) approaching the Rec. 2020 color gamut due to their extremely narrow emission bandwidth. Another important aspect are the high photoluminescence quantum yield (PLQY) values that can be obtained either in solution or thin films making these materials as promising candidates for optoelectronic applications such as LEDs or solar cells. Considerable research efforts in chemistry, chemical engineering, solid‐state physics, and material sciences have been made in the past years. The new opportunity in the field of semiconductor quantum dots is still in the beginning phase and is expected to remain active in the following years. Here, in this invited commentary, we briefly discuss and summarize the opportunities and challenges in both fundamental and technological aspects, based on our work and the recent work in this field.     

Achieving standard wide color gamut by tuning LED backlight and color filter spectrum in LCD

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.     

Generalized Gamut Mapping using Image Derivative Structures for Color Constancy

The gamut mapping algorithm is one of the most promising methods to achieve computational color constancy. However, so far, gamut mapping algorithms are restricted to the use of pixel values to estimate the illuminant. Therefore, in this paper, gamut mapping is extended to incorporate the statistical nature of images. It is analytically shown that the proposed gamut mapping framework is able to include any linear filter output. The main focus is on the local n-jet describing the derivative structure of an image. It is shown that derivatives have the advantage over pixel values to be invariant to disturbing effects (i.e. deviations of the diagonal model) such as saturated colors and diffuse light. Further, as the n-jet based gamut mapping has the ability to use more information than pixel values alone, the combination of these algorithms are more stable than the regular gamut mapping algorithm. Different methods of combining are proposed. Based on theoretical and experimental results conducted on large scale data sets of hyperspectral, laboratory and real-world scenes, it can be derived that (1) in case of deviations of the diagonal model, the derivative-based approach outperforms the pixel-based gamut mapping, (2) state-of-the-art algorithms are outperformed by the n-jet based gamut mapping, (3) the combination of the different n-jet based gamut mappings provide more stable solutions, and (4) the fusion strategy based on the intersection of feasible sets provides better color constancy results than the union of the feasible sets.     

Seventeen‐inch laser backlight in‐plane switching liquid crystal display with 8K, 120‐Hz driving,and BT.2020 color gamut

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.     

Special colour enhancement for three channels having similar radiances

A special enhancement algorithm is derived to colour separate ground-cover classes whose recorded wavelength distributions are similar but have significantly differing intensities. The special enhancement function is derived from considering the spectrum locus of a CIE 1931 (x,y) chromaticity diagram. By analogy with the relationship between the chromaticity co-ordinates and the channel radiance levels a function is derived that stretches the radiances to maximize the colour differences between such ground-cover classes. This Sinsusoidal Squeeze algorithm was applied to enhance the colour differentiation of Antarctic ice types as recorded by LANDSAT. A comparison between this special enhancement and the conventional colour composite results for Antarctic ice pack is presented. Field checks conducted during the 1980-81 Antarctic summer field season confirm our ability to delineate up to seven different types of ice by this technique. Additional applications of this special algorithm are believed to be forest class differentiation and bathymetric feature delineation.