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.     

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.     

New display concept for realistic reproduction of high-luminance colors

A new display concept for reproduction of high-luminance colors based on a liquid crystal display has been developed using a brighter backlight unit and color mapping algorithms. The new concept is able to display brighter colors close to a peak luminance of a display white than conventional displays so that realistic scene of brighter colors is better reproduced. It may also be one of the future display solutions needed to extend the color gamut in the direction of brighter colors, which is a principal limitation in conventional displays even in high-dynamic range display systems. With the new concept, an xvYCC- (extended-video YCbCr) compatible display can be easily realized.     

打印机和图像色域提取算法

针对当前色彩管理研究缺乏提取图像色域算法及可视化技术支持的现状，提出了一种打印机色域提取算法。先确定打印机色域边界点，通过这些边界点利用几何方法快速构造色域外壳，对设备色域进行精确描述，并对色域及其剖面进行真彩色可视化。利用对色域的剖分操作，构造基于剖面的色域匹配模型。     

Color‐tuning projection system for adaptive combination of high brightness and wide color gamut

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.     

一种基于图像空间频率特征的色域匹配算法*

色域匹配是色彩管理的一项关键技术。通过对彩色图像的特征描述的分析,提出了一种与图像空间特征相关的自适应色域匹配算法。该算法通过将图像增强技术与传统的色域匹配算法相结合,克服了传统算法不能同时保持明度对比度对比度和彩度的缺点,有效地提高了图像的再现效果和精度。     

基于B样条色域描述的颜色匹配

目前的色域匹配算法大多在等色调平面上进行,设备的色域边界以三角形近似描述,难以实现颜色的准确再现。该文分析了设备色域剖面的形状,提出了用准均匀B样条曲线来描述色域边界,设计了基于该样条曲线描述的CUSP色域匹配算法。实验结果表明,基于B样条色域描述的颜色匹配明显提高了色彩的再现精度,可显著提高打印输出彩图的质量。     

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.     

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.     

Power‐saving primary design for displays enclosing a target color gamut

Abstract— Display primaries are optimized for the trade‐off between the total primary power and color gamut under the requirement that a target color gamut is enclosed by the color gamut of the display. LED displays and HDTV color gamut are taken as examples. Compared to the display using a set of typical commercial RGB LEDs, it was found that a total optical (electrical) power of 23.6% (15.6%) can be saved for the display using optimal RGB LEDs. Although the size of the display color gamut is sacrificed, the color gamut of the display using optimal RGB LEDs still encloses the HDTV color gamut. The combined effect of the LED luminous efficiency and white‐point condition on the determination of the optimal LED wavelengths and bandwidths is also studied.     

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.     

Preferred and maximally acceptable color gamut for reproducing natural image content

Abstract— With the development of wide‐gamut display technology, the need is clear for understanding the required size and shape of color gamut from the viewers' perspective. To that end, experiments were conducted to explore color‐gamut requirements based on viewers' preferred level of chroma enhancement of standard‐gamut images. Chroma preferences were measured for multiple hues using single‐hue images, and a corresponding hue‐dependent preferred chroma enhancement was successfully applied to natural, multi‐hue images. The multi‐hue images showed overall success, though viewers indicated that reds could be decreased even further in colorfulness, and yellows could be increased, which may argue in favor of multi‐primary displays. Viewer preferences do vary within the population, primarily in overall chroma level, and the differences can be largely accounted for with a single parameter for chroma‐level adjustment that includes the preferred hue dependence. Image content dependencies were also found, but they remain too complex to model. The hue‐dependent chroma preference results can be applied to display design and color‐enhancement algorithms.     

Design of relative primary luminances for four-primary displays

Multi-primary displays have the advantage of large color gamut. The relative primary luminances of a conventional three-primary display are uniquely determined by its white point. There are N−3 degrees of freedom for choosing the relative primary luminances of an N-primary display with a given white point. This paper presents the methods designing the relative primary luminances of four-primary displays. A four-primary LED display is taken as an example for showing the methods. The maximum display luminance and color gamut are, respectively, taken as an additional requirement for determining the relative primary luminances of the display. The requirement of the maximum display luminance is taken for a set of available primary luminances. The gamut volume in CIELAB color space is defined for maximizing the display gamut. In practice, the design of the relative primary luminances may be a compromised result of the two additional requirements.     

激光显示中颜色系统的校正

激光显示作为一种新的显示技术它日益受到人们的关注。但是现有的显示制式只支持现有的显示系统当中的颜色转换,不支持激光显示的颜色转化,为了发挥激光显示色纯度高、色饱和度好、亮度高等优点,需要重新建立了一套适合激光显示的颜色转换系统。本文采用多元回归法来实现从CRT显示器到激光显示色域的转变,主要研究了实验样本数目、检验样本数目对结果的影响,采用了DPS数学软件系统对实验数据进行分析处理,建立了二阶多元回归的数学模型,并分析了模型的误差。选用二阶多元回归来预测和校正激光显示的显示效果,预测效果良好,误差较小。     

LED‐backlight feedback control system with integrated amorphous‐silicon color sensor on an LCD panel

Abstract— Thin‐film‐transistor liquid‐crystal displays (TFT‐LCDs) have the largest market share of all digital flat‐panel displays. An LCD backlighting system employing a three‐color red‐green‐blue light‐emitting diode (RGB‐LED) array is very attractive, considering its wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the high‐intensity LED has problems with thermal stability and degradation of brightness over time. Color and white luminance levels are not stable over a wide range of temperature due to inherent long‐term aging characteristics. In order to minimize color point and brightness differences over time, optical feedback control is the key technology for any LED‐backlight system. In this paper, the feasibility of an optical color‐sensing feedback system for an LED backlight by integrating the amorphous‐silicon (a‐Si) color sensor onto the LCD panel will be presented. To minimize the photoconductivity degradation of a‐Si, a new laser exposure treatment has been applied. The integrated color‐sensor optical‐feedback‐controlled LED‐backlight system minimized the color variation to less than 0.008 Δu'v' (CIE1976) compared to 0.025 for an open‐loop system over the temperature range of 42–76°C.     

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.     

Fast full‐color reflective display via photoluminescent enhancement

Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments.     

Attribute‐preserving gamut mapping of measured BRDFs

Reproducing the appearance of real‐world materials using current printing technology is problematic. The reduced number of inks available define the printer's limited gamut, creating distortions in the printed appearance that are hard to control. Gamut mapping refers to the process of bringing an out‐of‐gamut material appearance into the printer's gamut, while minimizing such distortions as much as possible. We present a novel two‐step gamut mapping algorithm that allows users to specify which perceptual attribute of the original material they want to preserve (such as brightness, or roughness). In the first step, we work in the low‐dimensional intuitive appearance space recently proposed by Serrano et al. [ SGM*16 ], and adjust achromatic reflectance via an objective function that strives to preserve certain attributes. From such intermediate representation, we then perform an image‐based optimization including color information, to bring the BRDF into gamut. We show, both objectively and through a user study, how our method yields superior results compared to the state of the art, with the additional advantage that the user can specify which visual attributes need to be preserved. Moreover, we show how this approach can also be used for attribute‐preserving material editing.