Color Filter Research Articles

P‐65: Strategic Realization of the Highest Possible Pixel Density for Quantum Dot Color Converter with Optimized Performance

The light extraction efficiency of QDCC (quantum dot color converter) is low when its aspect ratio (width to thickness ratio) of a subpixel is less than two, which causes the problem in their high‐resolution applications. Using QDPR (quantum dot photoresist) of high OD (optical density) values and PenTile subpixel arrangement, an apparent high‐resolution application is feasible, in which the QDCC film thickness is less than 2 μm. Further incorporation of yellow color filter film or color purified layer (CPL) on the QDCC film can optimize its optical performance. Theoretically, QDCC with pixel density over 3000 ppi is achievable when it is directly applied to the CMOS substrate. In a trial test QDCC is applied on a glass substrate, which results in pixel density of 2116 ppi and color gamut of NTSC 109.64%.

Machine Learning and Image-Processing-Based Method for the Detection of Archaeological Structures in Areas with Large Amounts of Vegetation Using Satellite Images

The detection of archaeological structures in satellite images is beneficial for archaeologists since it allows quick identification of structures across large areas of land. To date, some methods have been proposed to solve this task; however, these methods do not give good results in areas with large amounts of vegetation, such as those found in the southeast of Mexico and Guatemala. The method proposed in this paper works on satellite images obtained with SASPlanet. It uses two color spaces (RGB and HSL) and filters (Canny, Sobel, and Laplacian) jointly with supervised machine learning to improve the detection of archaeological structures in areas with a lot of vegetation. The method obtains an average performance of at least 93% on precision, recall, F1 score, and accuracy. Thus, our proposal is a very good option compared with traditional techniques for manual or semi-automatic detection of structures, identifying archaeological sites in a shorter time.

Joint demosaicking and denoising benefits from a two-stage training strategy

Image demosaicking and denoising are the first two key steps of the color image production pipeline. The classical processing sequence has for a long time consisted of applying denoising first, and then demosaicking. Applying the operations in this order leads to oversmoothing and checkerboard effects. Yet, it was difficult to change this order, because once the image is demosaicked, the statistical properties of the noise are dramatically changed and hard to handle by traditional denoising models. In this paper, we address this problem by a hybrid machine learning method. We invert the traditional color filter array (CFA) processing pipeline by first demosaicking and then denoising. Our demosaicking algorithm, trained on noiseless images, combines a traditional method and a residual convolutional neural network (CNN). This first stage retains all known information, which is the key point to obtain faithful final results. The noisy demosaicked image is then passed through a second CNN restoring a noiseless full-color image. This pipeline order completely avoids checkerboard effects and restores fine image detail. Although CNNs can be trained to solve jointly demosaicking–denoising end-to-end, we find that this two-stage training performs better and is less prone to failure. It is shown experimentally to improve on the state of the art, both quantitatively and in terms of visual quality.

Electrically Wavelength‐Controllable Color Filters with High Optical Transmittance Using Heterogeneous Chiral Liquid Crystals

AbstractOptical signals necessitate using filters that selectively transmit or reflect light with the desired wavelength information. In visual imaging‐related devices, a color filter acts as a wavelength selector to extract certain information from the incident light. To overcome the limitations of commercial pigmented color filters, structural color filters with controllable photonic bandgaps (PBGs) have recently attracted significant interest. Especially, chiral liquid crystal (CLC) has been widely investigated for tunable color filters owing to its selective reflection. However, most of the research has been limited to the control of conventional reflection rather than transmission wavelength. This study proposes an electrically wavelength‐tunable color filter with high optical transmittance using a heterogeneous CLC with extremely small voltages not exceeding 1.4 V. Electrothermal tuning of CLC is approached so that transmission wavelength of the device can be tuned among red, green, and blue. Moreover, analog pixel binning using CLC color filters is explored in a tetra‐layout beyond state‐of‐the‐art pixel binning with post‐capture digital image processing. Dynamic and direct binning can prevent the quality degradation of the images captured under low‐light illumination in image sensors. The wavelength‐tunable transmission color filter proposed in this study is expected to facilitate future electro‐optical dynamic color filter applications.

Media Affects in Dulac’s La Cigarette

With sensuality and innovation, French cinéaste Germaine Dulac illuminated the flaws in bourgeoise relationships. Her earliest extant film La Cigarette (1919) exposes the self-contempt that marriage breeds as it follows a husband’s suicidal mission. Fixated on living an “ideal,” patriarchal marriage, the husband falls into despair when his wife refuses to stay at home. His obsession reflects Sara Ahmed’s notion of happiness as a social obligation rather than a sincere feeling (The Promise of Happiness 2010). Beyond the diegesis, Dulac’s creative process and Marshall McLuhan’s analysis of the socio-technical climate’s influence on the psyche dovetail. Dulac aimed to transform the “unique ratios of sense perception” that McLuhan analyzes in The Medium is the Massage (41), and she succeeded by deploying all the technology at her disposal. In La Cigarette, color filters, iris lenses, and typographical variations collapse the happy marriage and wife-as-object norms. This disruption occurs most notably as the female body engages with music. Aurality along with visual-verbal texts exemplify what I am calling “media affects,” or the affective responses that emerge from Dulac optimizing her medium. This reading of La Cigarette synthesizes a media theory of perception (McLuhan), the affective object (Ahmed), and existing research on Dulac’s cinematography.

Longwave infrared multispectral image sensor system using aluminum-germanium plasmonic filter arrays

A multispectral camera records image data in various wavelengths across the electromagnetic spectrum to acquire additional information that a conventional camera fails to capture. With the advent of high-resolution image sensors and color filter technologies, multispectral imagers in the visible wavelengths have become popular with increasing commercial viability in the last decade. However, multispectral imaging in longwave infrared (LWIR, 8–14 μm) is still an emerging area due to the limited availability of optical materials, filter technologies, and high-resolution sensors. Images from LWIR multispectral cameras can capture emission spectra of objects to extract additional information that a human eye fails to capture and thus have important applications in precision agriculture, forestry, medicine, and object identification. In this work, we experimentally demonstrate an LWIR multispectral image sensor with three wavelength bands using optical elements made of an aluminum (Al)-based plasmonic filter array sandwiched in germanium (Ge). To realize the multispectral sensor, the filter arrays are then integrated into a three-dimensional (3D) printed wheel stacked on a low-resolution monochrome thermal sensor. Our prototype device is calibrated using a blackbody and its thermal output has been enhanced with computer vision methods. By applying a state-of-the-art deep learning method, we have also reconstructed multispectral images to a better spatial resolution. Scientifically, our work demonstrates a versatile spectral thermography technique for detecting target signatures in the LWIR range and other advanced spectral analyses.

A multi-channel approach for detecting tampering in colour filter images

Most devices capable of capturing photographs are provided with a Colour Filter Array (CFA). Images generated by these devices can be analysed to detect the so known CFA artefacts left by demosaicing methods. These artefacts are important in digital image forensics since they prove useful for determining the authenticity of an image. Previous works have focused exclusively on the analysis of the green band of the Bayer filter, neglecting the information in the remaining bands. In this work a process to estimate the pattern left by CFA artefacts regardless of their configuration is proposed, which can be used regardless of the size or colours used by the filter, or even in different colour spaces, obtaining in this way new sources of information for forensic analysis. A review and comparisons against state-of-the-art projects addressing the detection of manipulations using CFA artefacts are performed. The sensitivity of these proposals to post-processing methods such as compression and filtering will also be reviewed. We will also observe experimentally that the proposed technique can detect manipulations even in images affected by high levels of JPEG compression.

Plasmonic color filter with nanoring aperture array

The plasmonic color filter with sub-wavelength nanometal structure has the advantages that the traditional organic dye color filter cannot replace because of its unique characteristics. However, most plasmonic color filters have low selectivity and weak resonance. It limits their further applications and accuracy. We introduce a plasmonic color filter with a nanoring aperture array, which can exhibit high resonance intensity by fine-tuning the size of the outer aperture and the array period. Through COMSOL Multiphysics comprehensive verification, this may be potentially useful in micro- and nanodetection, optical imaging, optical filters, and other fields.

Deep learning-based real-time driving for 3-field sequential color displays with low color breakup and high fidelity.

Field sequential color liquid crystal displays (FSC-LCDs) are promising for applications needing high brightness and high resolution because removing color filters brings three times the light efficiency and spatial resolution. In particular, the emerging mini-LED backlight introduces compact volume and high contrast. However, the color breakup severely deteriorates FSC-LCDs. Concerning color breakup, various 4-field driving algorithms have been proposed at the cost of an additional field. In contrast, although 3-field driving is more desired due to fewer fields used, few 3-field methods that can balance image fidelity and color breakup for diverse image content have been proposed. To develop the desired 3-field algorithm, we first derive the backlight signal of one multi-color field using multi-objective optimization (MOO), which achieves a Pareto optimality between color breakup and distortion. Next, considering the slow MOO, the MOO-generated backlight data forms a training set to train a lightweight backlight generation neural network (LBGNN), which can produce a Pareto optimal backlight in real-time (2.3 ms on GeForce RTX 3060). As a result, objective evaluation demonstrates a reduction of 21% in color breakup compared with currently the best algorithm in color breakup suppression. Meantime, the proposed algorithm controls the distortion within the just noticeable difference (JND), successfully addressing the conventional dilemma between color breakup and distortion for 3-field driving. Finally, experiments with subjective evaluation further validate the proposed method by matching the objective evaluation.

Graphene/Cholesteric Liquid-Crystal-Based Electro-Driven Thermochromic Light Modulators toward Wide-Gamut Dynamic Light Color-Tuning-Related Applications.

Light filters are ubiquitous in projection and display techniques, illumination engineering, image sensing, photography, etc., while those enabling wide-gamut dynamic light color tuning are still lacking. Herein, by combining the electro-heating capability of graphene and unique optical properties (thermochromism and circular dichroism) of small-molecule-weight cholesteric liquid crystal (ChLC), a brand-new thermochromic light modulator is constructed as actively tunable color filter. Transparent graphene/glass hybrid with reasonably high conductivity serves both as a high-performance heater for actuating the thermochromism of temperature-responsive ChLC and as neutral light attenuator for brightness control. Thanks to the temperature- and polarization-dependent spectral properties of the ChLC, widely tunable hue and saturation properties of transmission light color are achieved, respectively. Several intriguing applications, e.g., color-variable smart windows for backlight color tuning and color-variable filters for photography, are also demonstrated. This work hereby provides new paradigms for promoting the applications of graphene/ChLC-based light modulators in next-generation light-management-related scenarios.

Preparation of Cholesteric Polymer Networks with Narrow-Bandwidth Reflection and Memory Effect

A polymer network with a memory effect based on a polymer-stabilized narrow-bandwidth cholesteric liquid crystal (CLC) was prepared using the washing-out/refill method. The effects of different polymerization conditions on the reflection properties of CLC films were investigated. Meanwhile, the selective reflection property and narrow-bandwidth reflection memory effect of the polymer network were proved, and the response mechanism was provided. Furthermore, different materials from liquid crystals, with an anisotropic refractive index, to toluene, with an isotropic refractive index, were refilled to polymer scaffolds with helical structures, which originated from the periodic arrangement of CLCs. It was confirmed that the reflection bandwidth of these films can be dramatically narrowed by the reduced birefringence (Δn) of the refilled materials. The narrowest bandwidth of 22.5 nm refilling toluene with an isotropic refractive index (Δn = 0) was obtained. These results may provide a novel idea for flexible reflective displays, color filters, printing, and colored cladding of a variety of objects.

Robust cascaded-parallel visual tracking using collaborative color and correlation filter models

Robust cascaded-parallel visual tracking using collaborative color and correlation filter models

Pixelated NIR–VIS Spectral Routers Based on 2D Mie‐Type Metagratings

AbstractThe out‐of‐band energy loss caused by in‐built color filters significantly degrades the signal‐to‐noise ratio and the dynamic range of conventional image sensors, which has restricted the attempt to develop ultrahigh‐density imaging devices by merely shrinking the pixel size. This issue will be more serious for security cameras, which need to collect both visible (VIS) and near‐infrared (NIR) light. The existing solutions mostly explore complex photonic nanostructures, which are often too complicated for production. In this work, a pixelated spectral router is demonstrated utilizing a 2D Si3N4 Mie‐type metagrating that can spatially divide NIR (850 nm) and VIS (400–700 nm) light to different pixels at high efficiencies. It has a minimum feature size larger than 360 nm, highly promising for massive production. Compared with the traditional filter design, this router can gain ≈42% and ≈30% signal enhancement for NIR and VIS bands, respectively. It is shown that it also has good polarization insensitivity and incident angle tolerance. The NIR–VIS simultaneous imaging is inspected without any complex reconstruction algorithm. Mode analysis indicates that the periodic interference of multipolar scattered fields caused by this metagrating provides the necessary degrees of freedom to spatially optimize the routing functions for broadband photons.

Design of non-Gaussian multispectral shortwave infrared filters assessed by surface spectral reflectances on the ECOSTRESS library.

This paper addresses the multispectral filter design problem for spectral ranges where a viewing subspace is not defined. The methodology of color filter design is extended to this case, which allows the optimization of custom filter transmittance that meets the physical constraints of available fabrication methods. Multispectral shortwave infrared filters are then designed for two scenarios: spectral reconstruction and false-color representation. The Monte Carlo method is used to verify the filter performance degradation due to deviations in fabrication. The results obtained indicate that the proposed method is useful for designing multispectral filters to be fabricated using generic processes without any additional constraints.

Proposed Extensions to the Third Edition of JPEG XS (ISO/IEC 21122) Standard

At its 94th meeting (17–21 January 2022), International Organization for Standardization (ISO)/IEC SC29WG1 (also known as JPEG Committee) decided to create a third edition of the JPEG XS standard (ISO/IEC 21122) for lightweight, low-latency image coding. While existing coding tools in the standard already support the compression of natural content and color filter array (CFA) RAW Bayer pattern data well, this third edition will extend the previous editions with coding tools that improve its performance on the compression of screen content and image sequences with static background. The first experiments demonstrate that the proposed coding tools can improve the average peak signal-to-noise ratio (PSNR) performance of JPEG XS on such sequences of more than 10 dB, and approximately 3 dB on computer-generated content. In this work, the authors will present the proposed coding tools and will evaluate their performance objectively by PSNR.

Design and development of Fabry–Perot etalon based color filter using ebeam GLAD technique: Simulation and experiment

The design of Spatial Variable Color Filter (SVCF), based on the principle of Fabry–Perot (FP) etalon, has been analyzed in detail considering Ag as reflecting metallic layer and TiO2 as cavity layer. The effect of different thickness ranges of cavity layer for different order of interference peaks and the effect of varying thickness of reflecting layer has been investigated through simulation. A SVCF has been designed in the broad visible wavelength range of 464 to 670 nm based on the 2nd order interference peak of FP etalon for optimized spectral performance and it has been experimentally demonstrated using ebeam evaporation technique. The reflecting Ag layer has been deposited at normal angle and the tapered cavity layer of TiO2 has been deposited at 86° glancing angle. The distribution of thickness and dispersion relationship at various locations of the glancing angle deposited (GLAD) TiO2 thin films has been analyzed by spectroscopic ellipsometry measurements. The effect of lateral variation of dispersion properties of cavity layer caused by GLAD, on the spectral performance of the developed SVCF, has been investigated by both simulation and through spectral transmittance measurement. Overall results demonstrate the potential of the axial glancing angle deposition technique for the first time for development of SVCF in visible wavelength with high peak transmittance (∼67%) and a peak wavelength tunability of ∼4 nm/mm.

Exploring the Arctic deep-sea by color filters


 
 
 
 
 
 
 
 Focus:
 To get to know some of the creatures in the deep-sea that use color and the lack of light to camouflage themselves.
 Learning objectives:
 With these TWO activities, we use vision to explore life forms in the deep sea which have adapted to extreme conditions. Through the activities, the pupils will also become familiar with some organisms well-hidden at the bottom of the ocean.
 Key words:
 Camouflage strategies, Deep sea ocean, Physical effects of light, Characteristics of sea lifeforms
 
 
 
 
 
 
 

Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures

Nanophotonics research has focused recently on the ability of nonlinear optical processes to mediate and transform optical signals in a myriad of novel devices, including optical modulators, transducers, color filters, photodetectors, photon sources, and ultrafast optical switches. The inherent weakness of optical nonlinearities at smaller scales has, however, hindered the realization of efficient miniaturized devices, and strategies for enhancing both device efficiencies and synthesis throughput via nanoengineering remain limited. Here, we demonstrate a novel mechanism by which second harmonic generation, a prototypical nonlinear optical phenomenon, from individual lithium niobate particles can be significantly enhanced through nonradiative coupling to the localized surface plasmon resonances of embedded gold nanoparticles. A joint experimental and theoretical investigation of single mesoporous lithium niobate particles coated with a dispersed layer of ~10 nm diameter gold nanoparticles shows that a ~32-fold enhancement of second harmonic generation can be achieved without introducing finely tailored radiative nanoantennas to mediate photon transfer to or from the nonlinear material. This work highlights the limitations of current strategies for enhancing nonlinear optical phenomena and proposes a route through which a new class of subwavelength nonlinear optical platforms can be designed to maximize nonlinear efficiencies through near-field energy exchange.

Grayscale-patterned integrated multilayer-metal-dielectric microcavities for on-chip multi/hyperspectral imaging in the extended visible bandwidth.

Pixelated filter arrays of Fabry-Perot (FP) cavities are widely integrated with photodetectors to achieve a WYSIWYG ("what you see is what you get") on-chip spectral measurements. However, FP-filter-based spectral sensors typically have a trade-off between their spectral resolution and working bandwidth due to design limitations of conventional metal or dielectric multilayer microcavities. Here, we propose a new idea of integrated color filter arrays (CFAs) consisting of multilayer metal-dielectric-mirror FP microcavities that, enable a hyperspectral resolution over an extended visible bandwidth (∼300 nm). By introducing another two dielectric layers on the metallic film, the broadband reflectance of the FP-cavity mirror was greatly enhanced, accompanied by as-flat-as-possible reflection-phase dispersion. This resulted in balanced spectral resolution (∼10 nm) and spectral bandwidth from 450 nm to 750 nm. In the experiment, we used a one-step rapid manufacturing process by using grayscale e-beam lithography. A 16-channel (4 × 4) CFA was fabricated and demonstrated on-chip spectral imaging with a CMOS sensor and an impressive identification capability. Our results provide an attractive method for developing high-performance spectral sensors and have potential commercial applications by extending the utility of low-cost manufacturing process.

Inverse design of dynamically tunable phase-change material based metamaterial absorber induced structural color

Structural colors using phase change material based metasurfaces/metamaterials have enabled high saturation, high resolution, and wide-gamut color printing. The wide color gamut with high resolution is achieved by changing the geometry of the metamaterials. However, finding the design parameter for desired color is computationally costly. Designing such parameters to precisely show the required color is therefore essential for producing metamaterials for use in real-world applications. In this work, we report a tunable reflective metamaterial using Ge2Sb2Te5 (GST) for the generation of structural colors. Exploiting the large contrast in refractive index of GST with the change in phase we can dynamically tune between two different colors. Further, we report an inverse design of tunable reflective metamaterial structure using deep neural network. The inverse design based on bidirectional artificial neural network can accurately predict the design parameter for a desired color. Our results show that tunable color filters using GST nanostructures can be designed accurately and efficiently using deep neural networks and could find potential applications in color printing and display technologies.