Development of photonic crystal composites for display applications

Abstract— With an ever‐increasing demand for bigger, brighter, and more‐efficient displays, the research into new display technologies is consistently vibrant and groundbreaking. In this paper, a new type of display material based on the electrical actuation of photonic crystals is described. This material, called Photonic Ink, is capable of reflecting bright and narrow bands of color tunable throughout the entire visible spectrum as well as into the UV or NIR. P‐Ink devices are switched at low voltage and display electrical bistability, leading to very low power consumption. The characteristics of the P‐Ink material make it a viable option for color‐based reflective‐display devices.     

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.     

Optically adjustable display color gamut in time-sequential displays using LED/Laser light sources

Recently, various wide color gamut displays have been developed. Because of color gamut differences between wide gamut displays and the standard definitions, the color reproduction on such display system is not equal to original images. To overcome this, a color transformation such as gamut mapping algorithm is applied in conventional systems. But this manipulates only the video signal that would reduce the signal dynamic range and produces quantization error of video signal.In this paper, we propose a new optical Color Gamut Processing instead of an image data mapping. In the method, an individual color gamut of the standard definitions can be composed of an optical mixture of original primary colors. As a result, a perfect color match for the various standards can be realized within a display gamut without any signal artifacts.Moreover the same concept is applied to the video stream in order to elevate scene luminance. A scene-adaptive Dynamic Color Gamut Processing measures a color gamut for every video frame and adjusts a matched display color gamut so that it is able to increase display contrast in comparison to conventional display systems.     

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.     

Non‐metamerism of boundary colors in multi‐primary displays

Abstract— A control sequence gives the intensities of the primaries for a pixel of a display device. The display gamut, i.e., the set of all the colors that a display can produce, is a zonohedral subset of CIE XYZ space and contains both boundary and interior colors. Displays with four primaries or more exhibit metamerism, in which different control sequences produce colors that appear identical to an observer. This paper shows mathematically that, provided no three primaries are linearly dependent, metamerism can only occur for interior colors. When there are four or more primaries, metamers can always be found for interior colors. A color on the gamut boundary, by contrast, is only produced by a unique control sequence. The proof used for displays can be extended to object‐color solids, to show that optimal colors, which are on the boundary of an object‐color solid, have unique reflectance functions.     

Review Paper: Multi‐primary‐color displays: The latest technologies and their benefits

Abstract— Multi‐primary‐color (MPC) display technology is one of the fastest emerging research areas in recent years. Wide‐color‐gamut display devices have been required for visually sufficient and/or accurate color reproduction. It is well known that MPC displays can reproduce accurate colors with high efficiency. In addition, not only the image‐quality improvement but some other performance of display devices is also required for display devices. This paper reviews achievements in MPC display technologies and focuses on the benefits of MPC displays: power‐savings and high resolution.     

Optical characterization of autostereoscopic 3‐D displays

Abstract— Display‐measurement methods different from conventional 2‐D display measurements are needed for verifying the optical characteristics of autostereoscopic (3‐D) displays and for comparing different 3‐D display technologies. Industry is lacking standardized measurement methods, and the reported results can not always be compared. The selected set of characteristics discussed in this paper and partly defining the quality of the 3‐D experience are crosstalk, viewing freedom, and optimum viewing distance. Also, more conventional display characteristics such as luminance are discussed, since the definitions for these characteristics in 3‐D mode usually differ from those used for the 2D displays. We have investigated how these chosen 3‐D display characteristics can be objectively measured from transmissive two‐view and multiview 3‐D displays. The scope of this article is to generally define those basic characteristics as well as the different measurement methods. Most of the 3‐D characteristics can be derived from the luminance and colors versus the viewing angle. Either a conoscopic or a goniometric measurement system can be used, as long as the angular and stray‐light properties are suitable and known. The characteristics and methods are currently discussed in the display‐quality standardization forums.     

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.     

Diffractive backlight grating array for mobile displays

Abstract— The display backlight unit (BLU) is the most power‐consuming subunit in mobile liquid‐crystal displays. The state‐of‐the‐art BLUs utilize scattering, refractive, and reflective microstructures to generate a uniform distribution of white light through the display. More effective means of transmitting light through the display color filters could be obtained by using diffraction, but previously proposed diffractive backlights do not fully utilize all the possibilities to design gratings effectively for optimal color separation and outcoupling. This paper presents a new pixelated diffractive backlight grating array as an approach for overcoming these obstacles in BLU design. A model array was fabricated to couple out red, green, and blue primary colors from the respective subpixel locations. The results show that it is possible to manufacture such an array and that the light couples out as intended, giving a starting point to design mobile‐display modules with low light‐transmission losses.     

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.     

An observer‐metamerism sensitivity index for electronic displays

The effect of observer metamerism induced by electronic displays depends to a large extent on their primary spectra (red, green, and blue in the most common case). In particular, for narrow‐band primary spectra whose peak wavelength lies in the range of high variability of the observer's color‐matching function, some observers can experience very large differences between actual surface colors (e.g. in a light booth) and displayed colors if the monitor is optimized for the International Commission on Illumination (CIE) 1931 standard observer. However, because narrow‐band light‐emitting diodes lead to larger color gamuts, more and more monitors with very narrow band primaries are coming onto the market without manufacturers taking into account the associated problem of observer variations. Being able to measure these variations accurately and efficiently is therefore an important objective. In this paper, we propose a new approach to predict the extent of observer metamerism for a particular multiprimary display. Unlike existing dedicated models, ours does not depend on a reference illuminant and a set of reflectance spectra and is computationally more efficient.     

Optimal and acceptable color ranges of display primaries for mobile applications

Abstract— For many new display types, especially for mobile applications, the chromaticity coordinates of the primaries differ from those recommended by the EBU (European Broadcast Union). In order to identify optimal and acceptable ranges in which these primary colors may vary two studies were conducted: one related to the hue of the primaries [also reported in an earlier paper (Ref. 4)] and one related to their saturation. In the first part of the present study, observers set the saturation of one single primary (red, green, or blue) separately or of all three primaries simultaneously, to an optimum, for seven different (natural) images. In the second part, the same observers decreased the saturation until they perceived the image as “just acceptable” (defined as “having natural colors, given its content”). Both parts were conducted on an LCD monitor and repeated later with a different group of subjects on a CRT monitor. In this paper, the results of the current study are reported and they are combined with the results of the previous one. The results of the experiments show that for optimal image quality the saturation of the red and green primaries of a display must be at least 90% with respect to the EBU standard. For the blue primary it can be somewhat lower (at least about 70%). In the acceptance task, observers were the least tolerant in accepting a saturation reduction of the red primary (70%) and the green primary (60%) and they were almost twice as tolerant for the blue primary (35%). Ellipses were fitted to the results of the hue and saturation studies in 1976 CIE (u'v')color space such that display manufacturers can easily test whether the color reproduction of their displays is optimal, acceptable, or unacceptable with respect to reproducing natural colors.     

Brilliant cosmetic film for ambient displays,with cholesteric liquid crystal

We have successfully developed a cosmetic film with polymerized cholesteric material. The film features a variety of colors by helical pitch gradients, diffusive texture, and arbitrary color patterns. It hides the display when turned off, and transmits display images when turned on. We believe it could change the display in the OFF‐state from the conventional black wall to specially designed decorations. In addition, they can be applied to hidden sensors.     

Conventional vehicle display panels: the drivers' operative images and directions for their redesign

The proliferation of new displays in modern vehicles sets the challenge to revisit the design of the conventional display units, toward more simplified appearance. The present study aims to evaluate the usefulness of the information provided to the drivers by the conventional vehicle display units, in order to trace directions that would lead to a simplification of the future display panels. Based on the concept of operative images, two working hypotheses were formulated: (i) the experienced drivers have developed an operative image-reference (OI-R) for the display panel of their own vehicle(s), reflecting the relative importance they attribute to the information emitted by the various displays of the panel, and (ii) the experienced drivers' drawings of the display panel of their own vehicle will be guided by their OI-R for it - providing therefore traces of the content of their OI-R, while the less experienced drivers' drawings will be closer to the actual display panel of their own vehicle. The method of drawing from memory was used to obtain traces of the operative images of both experienced and less experienced non-professional drivers. The obtained 335 drawings were compared to the actual display panels, as to their overall resemblance and to specific features. The results of the data analysis are in accordance to our working hypotheses. Considering the main features of the experienced drivers' OI-R, directions for the simplification of the appearance of conventional display units are proposed.     

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.     

Visualizing color gamuts: a user interface for the effective use ofperceptual color spaces in data displays

The advantages of using perceptually uniform color spaces in data displays are described. It is shown how one-, two-, and three-dimensional representations of color gamuts can provide an understanding, at various visualization levels, of the colors that can be produced on display devices, of how they restrict color displays in practice, and of how they form an essential part of a user interface in the design of color displays     

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.     

Confined‐error‐diffusion algorithm for flat‐panel display

Abstract— The reduction of a structural pattern at specific gray levels caused by digital halftone methods is the subject of this paper. This problem is more severe in some flat‐panel displays because their black levels typically are brighter than other display blocks. A patented halftone algorithm, confined error diffusion (CED), that confines the error‐carry within the dither mask is described and extended. First, the CED algorithm that dynamically applies random error diffusion or the ordered‐dither method, depending upon image content, is described in detail. Finally, we propose an advanced CED algorithm for improving the gradation characteristics of the CED algorithm. The performance of the proposed algorithms is compared to the experimental results for natural test images. In order to verify the halftone quality, a structural similarity measure for color images by taking into account the interrelation between color channels is proposed, and the results based on the proposed method, the color similarity measure method, is given.     

A study of the relationship between color-concept association and occupational background for Chinese

BackgroundThe use of colors in visual displays can facilitate visual search and perception, but their use may not be effective without consideration of differences in the interpretation of their connoted meanings between individuals of different occupational backgrounds.ObjectiveThis study examined color-concept associations for Hong Kong Chinese students and white-collar workers, and then compared their associations with those of two other occupational groups to assess whether occupational background is related to color-concept associations.MethodA questionnaire survey was used to examine color-concept associations among 100 university students and 100 white-collar workers in Hong Kong. The participants were presented with 16 safety-related concepts and were asked to choose one of 10 colors that best represented each concept. The associations reported by four groups with different occupations (the two groups in this study and the groups of managerial staff and steel workers examined in our previous study) were compared. A chi-square test was applied to determine whether significant color association(s) existed for each concept.ResultsOur results revealed that each concept was significantly associated with at least one color (p < 0.01). The Hong Kong white-collar workers and managerial staff in mainland China both expressed the same color associations for 14 of the tested concepts, and differed only over which colors were associated with “strong,” and “radiation hazard.” These findings generally suggest that populations with similar occupations can have similar color perceptions. However, the students and the other three employee groups reported different color associations with the concepts “normal,” “off” and “potential hazard.”ConclusionsOccupational background is associated with how color is interpreted for its connoted meaning. One should consider occupational background carefully when choosing colors in product designs, especially for safety.     

Extensible multi‐primary control sequences

Abstract— In a display with more than three primaries (called a multi‐primary display), a color can be expressed as multiple combinations (called control sequences) of primaries. This paper presents an algorithm for assigning control sequences that preserves current assignments when further primaries are added. These control sequences are cal led extensible. It is shown that the gamut of any number of primaries is a zonohedron, which can be dissected into parallelepipeds. Control sequences are assigned within each parallelepiped. The current parallelepipeds remain when more primaries are added, so the current assignments are preserved. Multi‐primary displays can also cause unwanted metamerism and make continuous color scales appear discontinuous. The algorithm avoids these problems. When viewed through natural filters, such as yellowed ocular lenses, multi‐primary displays can sometimes make two different colors appear identical. If the primaries satisfy the Binet—Cauchy criterion, which is always the case when all primaries are monochromatic, then these spurious matches are avoided.