Color Filter Research Articles

The Spectrum of Light Emitted by LED Using a CMOS Sensor-Based Digital Camera and Its Application.

We introduced a digital photo image analysis in color space to estimate the spectrum of fluor components dissolved in a liquid scintillator sample through the hue and wavelength relationship. Complementary metal oxide semiconductor (CMOS) image sensors with Bayer color filter array (CFA) technology in the digital camera were used to reconstruct and decode color images. Hue and wavelength are closely related. To date, no literature has reported the hue and wavelength relationship measurements, especially for blue or close to the UV region. The non-linear hue and wavelength relationship in the blue region was investigated using a light emitting diode source. We focused on this wavelength region, because the maximum quantum efficiency of the bi-alkali photomultiplier tube (PMT) is around 430 nm. It is necessary to have a good understanding of this wavelength region in PMT-based experiments. The CMOS Bayer CFA approach was sufficient to estimate the fluor emission spectrum in the liquid scintillator sample without using an expensive spectrophotometer.

Photosensitivity and filter efficacy in albinism✰

PurposeTo describe the prevalence and severity of photosensitivity in patients with albinism, and to compare with ocular features and how this correlated with use and choice of optical filters. MethodsCross-sectional study on 81 participants with ocular or oculocutaneous albinism. An ophthalmic evaluation including visual acuity, contrast sensitivity and evaluation of iris translucency and fundus hypopigmentation was performed. Participants were offered optical rehabilitation with testing of a wide panel of filters. The associations between ocular characteristics, subjective photosensitivity complaints, and filter choice were evaluated. ResultsPhotosensitivity was rated as “some” to “worst imaginable” in 77.8% of participants. Severity of photosensitivity correlated significantly with fundus hypopigmentation (p = 0.04) but not with iris translucency (p = 0.14) and it was worse in those with poor visual acuity but there was no association between photosensitivity and contrast vision. Seventy-four new pairs of spectacles were prescribed in the study. All outdoor spectacles contained a filter, whereas 26.5% of new indoor spectacles did not. Relatively neutral filter colors (gray, brown or a combination of gray and brown with other colors) and low transmission were preferred. DiscussionPhotosensitivity is common in albinism, but research targeting treatment is limited. Color and neutral filters with a low light transmission were preferred, with participants having a large number of spectacles, presumably to meet their needs in different situations.

Optical Rotation‐Based Tunable Color Filter Using Chiral Photonic Crystal

AbstractRecently, tunable color filters have been desirable for various applications such as tunable colored glasses, camouflage materials, smart labels, smart windows, and dynamic displays. An optical rotation‐based color tuning (ORCT) method is presented here, which is a cost‐effective and nondestructive way to provide a wide range of color tunability using a controlled cholesteric liquid crystal (CLC) as a chiral photonic crystal and two polarizers. Moreover, the color range of the ORCT can be manipulated by engineered optical rotation of the CLC film, which is verified by numerical calculations and experiments. As a proof of concept, tunable color filters are demonstrated to attenuate unexpected light sources and provide better visibility. We believe that our ORCT technology can be a cornerstone in potential color variation applications.

Spectral Reflectance Recovery from the Quadcolor Camera Signals Using the Interpolation and Weighted Principal Component Analysis Methods.

The recovery of surface spectral reflectance using the quadcolor camera was numerically studied. Assume that the RGB channels of the quadcolor camera are the same as the Nikon D5100 tricolor camera. The spectral sensitivity of the fourth signal channel was tailored using a color filter. Munsell color chips were used as reflective surfaces. When the interpolation method or the weighted principal component analysis (wPCA) method is used to reconstruct spectra, using the quadcolor camera can effectively reduce the mean spectral error of the test samples compared to using the tricolor camera. Except for computation time, the interpolation method outperforms the wPCA method in spectrum reconstruction. A long-pass optical filter can be applied to the fourth channel for reducing the mean spectral error. A short-pass optical filter can be applied to the fourth channel for reducing the mean color difference, but the mean spectral error will be larger. Due to the small color difference, the quadcolor camera using an optimized short-pass filter may be suitable as an imaging colorimeter. It was found that an empirical design rule to keep the color difference small is to reduce the error in fitting the color-matching functions using the camera spectral sensitivity functions.

White luminescent calcium molybdate phosphor synthesized at room temperature via the Co-precipitation method used in a LED flexible composite

To synthesize a white light-emitting phosphor, Dy3+, a rare earth ion, was added to synthesize crystalline CaMoO4 at room temperature by co-precipitation. In the synthesized powder, the main peak of the (112) plane was clearly observed in the x-ray diffraction pattern, and it was observed that the lattice constant was changed by the addition of the Dy3+ ions. The synthesized phosphor showed a strong absorption in the ultraviolet region and both blue light emission from the host and yellow light emission by the Dy3+ ions and cold white light emission. A flexible composite was prepared by mixing the synthesized phosphor powder with a PDMS polymer. It showed white light emission when placed on a UV-LED with an applied voltage, suggesting that it can be used as an LED color filter.

Bulk-Heterojunction Adjustment Enables a Self-filtering Organic Photodetector with a Narrowband Response.

Image-sensor technology is the foundation of many emerging applications, where the photodetector is designed to interact with incoming photons that have specific colors or wavelengths. A color filter is therefore crucial to enable the selective spectral response of the photodetector and to eliminate the crosstalk interference resulting from ambient lights. Unfortunately, a reduced detection sensitivity of the photodetector is inevitable due to an imperfect light filtering, which greatly limits the practical applications of selective-response photodetectors. Herein, we demonstrate a bulk-heterojunction (BHJ) organic composite featuring a self-filtering light responsive characteristic. Through a careful optimization of the BHJ film, the organic photodetector (OPD) demonstrates a high-selective spectral response to the infrared (IR) radiation without the need of applying a color filter. As a result, the self-filtering top-illuminated OPD exhibits a narrowband external quantum efficiency (EQE) of 53% with a narrow full width at half-maximum (fwhm) of 56 nm centering at 1080 nm. A high responsivity of 0.46 A W-1 is also achieved at 1080 nm wavelength due to the self-filtering characteristic.

Angle-invariant eye-friendly color filter capitalizing on a multi-layer nano-resonator integrated with highly reflective/absorbing media.

Color filter with a combination of excellent angle insensitivity and high near-infrared shielding absorption is essential to broaden its practical application of harsh environment. However, there are few attention on the near-infrared absorption of color filter, prominent to the protection of human eyes in some special application scenarios. Herein, we propose and develop a dual-function color filter composed of four-layer silicon/titanium planar nanostructure that integrates with both angle-invariance and near-infrared shielding. The proposed color filter enables the creation of three reflective color primaries of cyan, yellow, and magenta (CYM) employing a combination of Fabry-Perot resonance and anti-resonant effect with the tuning of silicon thickness. The created reflective colors are less sensitive over a wide angle of incidence up to 60°, where the center wavelength of optical spectra is shifted by below 1.8%. Besides the angle-invariant performance, the color filter can effectively shield near-infrared light with a 70% average absorption under normal incidence. Moreover, this filter's thermal stability at 500°C demonstrates its feasibility for extreme environments. The demonstrated color filter is suitable for architectural decorative coatings and outdoor protective coatings in some harsh environment with strong near-infrared radiation, such as glass smelting, steel forging, and long-term sunlight exposure.

Changes in structure and luminescence properties according to the Tb3+ doping concentration of crystalline BaMoO4 synthesized at room temperature and application in LED color filters

Changes in structure and luminescence properties according to the Tb3+ doping concentration of crystalline BaMoO4 synthesized at room temperature and application in LED color filters

All-dielectric metasurface with ultrahigh color filtering and polarization-independent/dependent characteristics

The all-dielectric metasurface-based color filter (CF) has attracted huge interest in many fields due to its excellent optical properties. We present four metasurface-based CFs with different shapes on quartz substrates to generate blue (B), green (G), and red (R) spectra with high color purity. CFs show the maximum reflection intensities of 99.6% (B), 99.7% (G), and 95.1% (R), and their spectra bandwidths are 14, 16, and 13 nm for RGB colors, respectively. These proposed metasurface-based CFs possess high color saturation and ultra-narrow bandwidths. In addition, CFs with different shapes show the tunability of color switching and polarization-dependent characteristics. These CF designs will potentially benefit reflective display technologies, and the ultrahigh color filtering characteristics of CF-1 and CF-2 are particularly useful for high-resolution color printing and micro-LED. Moreover, the polarization-dependent characteristics of CF-3 and CF-4 make it possible for them to be applied as polarization switches, tunable color switches, and so on.

All‐Recyclable Triboelectric Nanogenerator for Sustainable Ocean Monitoring Systems (Adv. Energy Mater. 30/2022)

Triboelectric Nanogenerators In article number 2201341, Jun-Ho Jeong, Il-Kwon Oh, Inkyu Park and co-workers develop an all-recyclable triboelectric nanogenerator (AR-TENG) that exhibits high power density and excellent mechanochemical stability. The recyclability is demonstrated through its disassembly and fabrication of a plasmonic color filter. An ocean energy harvesting system based on the AR-TENG is developed and used to power a buoy-type ocean monitoring system and intelligent life jacket.

Ultra-Thin and Lithography-Free Transmissive Color Filter Based on Doped Indium Gallium Zinc Oxide with High Performance.

A kind of ultra-thin transmissive color filter based on a metal-semiconductor-metal (MSM) structure is proposed. The displayed color can cover the entire visible range and switches after H2 treatment. An indium gallium zinc oxide (IGZO) semiconductor was employed, as the concentration of charge carriers can be controlled to adjust the refractive index and achieve certain colors. The color modulation in the designed structure was verified using the rigorous coupled wave analysis (RCWA) method. The angular independence of the relative transmission could reach up to 60°, and polarization-insensitive performance could also be maintained. Numerical results demonstrated that the thickness of IGZO was the key parameter to concentrate the incident light. The overall structure is planar and lithography-free and can be produced with simple preparation steps. The obtained results can also be extended to other similar resonators where a proper cavity allows dynamical functionality.

Design, synthesis and properties of zinc phthalocyanine dyes for color photoresist

<p indent="0mm">The color photoresist is one of the important parts of color filter, and it is an important material for realizing the color display of TFT-LCD. To overcome low color purity and dimness of color properties, dyes can be attractive alternatives for the pigment. However, it is hard to accomplish in industrial production owing to the poor thermal stability of dyes-based color filters. In order to investigate the effects of different substituents on dye solubility and thermal stability, a series of zinc phthalocyanine dyes were designed and synthesized in this study. The results indicated that sulfone was modified in chloro-zinc phthalocyanine dyes showing better solubility and thermal stability, which is of great importance for the design of zinc phthalocyanine molecular-dyes for color photoresists.

Optical barcoding using polarisation sensitive plasmonic biosensors for the detection of self-assembled monolayers

Periodic subwavelength apertures have the ability to passively detect variations in the dielectric properties of the local sample environment through modification of the plasmon resonances associated with these structures. The resulting resonance peak can effectively provide a ‘fingerprint’ indicative of the dielectric properties of the medium within the near-surface region. Here we report on the use of bimodal silver-based plasmonic colour filters for molecular sensing. Firstly, by exploring the optical output of these devices as a function of the incident polarisation for a range of different analytes of known refractive index, we were able to both maximise and quantify their sensitivity. We then apply this concept to the real-time monitoring of the formation of self-assembled monolayers based on detection of the optical output using a spectrometer. This highlights the potential for bimodal plasmonic devices to be able to dynamically monitor variations in the local environment down to the level of single molecules without the need for specific functionalisation or labelling. Advantages of using this technique include the ability for these devices to be miniaturised and to dynamically tailor their optical output permitting the analysis of very small sample volumes and maximise their dynamic range for a specific analyte.

Discussion of Novel Filters and Models for Color Space Conversion

In the era of artificial intelligence perceptual algorithms used in state-of-the-art Advanced Driver Assistance Systems (ADAS), algorithm validation is not an easy task. To ensure the highest possible safety level of the solution, the performance of the algorithm must be evaluated under a variety of challenging conditions. To test the algorithms, simulators are used to emulate the virtual environment around the car taking into account road traffic, infrastructure and vehicles dynamics. Sensor models are necessary for virtual testing to provide required data to ADAS algorithms. This article introduces the issue of modeling the color filter spaces that are used in the automotive industry. The images generated by the simulator usually have RGB color. In contrast, the automotive industry uses filters such as RCCC and RYYCy. In this paper, the methods for transforming color space from RGB to RYYCy are discussed. Three novel approaches are introduced to solve this problem: analytical, polynomial, and based on a neural network. Moreover, comparative discussion of the presented solutions is shown and with the set of experiments the conversion accuracy and execution time of each algorithm are compared. In addition, introduced solution were compared with modified models that are presented in the literature.

Electrochromic soft contact lenses with built-in non-interfering, high-efficient dual-band wireless power transfer system

Color contact lenses attracts considerable attention for vision management and cosmetic applications nowadays. However, they require a wired power supply system because positive and negative voltages need to be applied for color modulation of electrochromic coating on the lens. This study demonstrates a wireless-powered electrochromic soft contact lens that modulates color using a dual-band wireless power transfer (WPT) system. The stretchable and conductive electrochromic film is the result of fabrication by spin-coating a mixed solution comprising PEDOT:PSS for the electrical conductor, polyurethane for the stretchable supportive layer, ethylene glycol, and dodecylbenzene sulfonic acid as conductivity enhancers. The dual-band system for negative voltage at 13.56 MHz and positive voltage at 28.4 MHz consists of two resonators using semi-loop antennas connected in parallel with capacitors. The dual-band resonators and electrochromic films are electrochemically bonded onto a commercially available soft contact lens. The proposed lens is capable of reversibly and wirelessly modulating the color from transparent to dark blue for several tens of seconds and usable as wireless color filters and Morse code transmitters.

Volumetric Lagrangian Particle Velocity And Temperature Measurements In Large Aspect Ratio Rayleigh-Bénard Convection

Rayleigh-Bénard convection (RBC) is a well-known model experiment for temperature-driven flows. Even though RBC has been studied for decades, many open questions remain. Temporally and spatially resolved temperature and velocity data are crucial for a better understanding of the underlying physics. This paper proposes a new approach that combines Lagrangian Particle Tracking (LPT) with Particle Image Thermometry (PIT). The combined measurement techniques should be utilized to investigate the flow inside a large aspect ratio RBC cell with a lateral size of w = 700 mm and a height h = 28 mm, which corresponds to an aspect ratio of 25. Due to the large aspect ratio, the cameras observe the flow through the transparent cooling plate. We show that LPT of thermal convection flows within the setup can be performed successfully. Subsequently, we describe the temperature measurement technique PIT based on Thermochromic Liquid Crystals (TLCs) and discuss and quantify the additional challenge arising from color imaging of small particles. Namely, the sparse color sampling of a color filter array (CFA) camera and chromatic dispersion resulting from the oblique viewing angle of the color camera. To circumvent the sparse sampling of the CFA camera, we use a three-chip camera that resolves each color (red, green, blue) at full sensor resolution. We quantify the influence of the chromatic dispersion by cross-correlating the color channels. We then apply the resulting disparity maps in a correcting step to reduce the disparities by shifting the red and blue towards the green channel. The visual comparison of the corrected and uncorrected images shows a reduction in the color dispersion. Beyond that, the remaining disparities between the colors of the corrected images are minimal. This indicates that the correction step is useful to increase the quality of the particle images for temperature estimation.

Stabilization of spherical videos based on feature uncertainty

Nowadays the trend is to acquire and share information in an immersive and natural way with new technologies such as Virtual Reality (VR) and 360^{circ } video. However, the use of 360^{circ } video, even more the use of VR head-mounted display, can generate general discomfort (“cybersickness”) and one factor is the video shaking. In this work, we developed a method to make the viewing of 360^{circ } video smoother and more comfortable to watch. First, the rotations are obtained with an innovative technique using a Particle Swarm Optimization algorithm considering the uncertainty estimation among features. In addition, a modified Chauvenet criterion is used to find and suppress outliers features from the algorithm. Afterward, a time-weighted color filter is applied to each frame in order to handle also videos with small translational jitter, rolling shutter wobble, parallax, and lens deformation. Thanks to our complete offline stabilization process, we achieved good-quality results in terms of video stabilization. Achieving better robustness compared to other works. The method was validated using virtual and real 360^{circ } video data of a mine environment acquired by a drone. Finally, a user study based on a subjective and standard Simulator Sickness Questionnaire was submitted to quantify simulator sickness before and after the stabilization process. The questionnaire underlined alleviation of cybersickness using stabilized videos with our approach

Machine learning-assisted design of polarization-controlled dynamically switchable full-color metasurfaces.

Dynamic color tuning has significant application prospects in the fields of color display, steganography, and information encryption. However, most methods for color switching require external stimuli, which increases the structural complexity and hinders the applicability of front-end dynamic display technology. In this study, we propose polarization-controlled hybrid metal-dielectric metasurfaces to realize full-color display and dynamic color tuning by altering the polarization angle of incident light without changing the structure and properties of the material. A bidirectional neural network is trained to predict the colors of mixed metasurfaces and inversely design the geometric parameters for the desired colors, which is less dependent on design experience and reduces the computational cost. According to the color recognition ability of human eyes, the accuracy of color prediction realized in our study is 93.18% and that of inverse parameter design is 92.37%. This study presents a simple method for dynamic structural color tuning and accelerating the design of full-color metasurfaces, which can offer further insight into the design of color filters and promote photonics research.

High performance of transmissive color filter with hybrid Tamm plasmon-cavity

High performance of transmissive color filter with hybrid Tamm plasmon-cavity

Coloured filters can simulate colour deficiency in normal vision but cannot compensate for congenital colour vision deficiency

Red-green colour vision deficiency (CVD) affects ~ 4% of Caucasians. Notch filters exist to simulate CVD when worn by colour vision normal (CVN) observers (simulation tools), or to improve colour discrimination when worn by CVD observers (compensation tools). The current study assesses effects of simulation (Variantor) and compensation (EnChroma) filters on performance in a variety of tasks. Experiments were conducted on 20 CVN and 16 CVD participants under no-filter and filter conditions (5 CVN used Variantor; 15 CVN and 16 CVD used EnChroma). Participants were tested on Ishihara and Farnsworth-Munsell 100 hue tests, CVA-UMinho colour discrimination and colour naming tasks and a board-game colour-sorting task. Repeated-measures ANOVAs found Variantor filters to significantly worsen CVN performance, mimicking protanopia. Mixed-model and repeated-measures ANOVAs demonstrate that EnChroma filters do not significantly enhance performance in CVD observers. Key EnChroma results were replicated in 8 CVD children (Ishihara test) and a sub-sample of 6 CVD adults (CVA-UMinho colour discrimination and colour naming tasks) for a smaller stimulus size. Pattern similarity exists across hue for discrimination thresholds and naming errors. Variantor filters are effective at mimicking congenital colour vision defects in CVN observers for all tasks, however EnChroma filters do not significantly compensate for CVD in any.