Design of non-polarizing color splitting filters used for projection display system

Optical thin films used at oblique incidence exhibit inevitable polarization dependent properties. In reflective projection display systems, Philips prisms with color splitting filters are widely used. Generally, illuminating light at different polarization components passes the color splitting filters twice in such Philips prism. Color splitting filters operate as color separation for s-polarization and as color recombination for p-polarization, and thus performances of the color splitting filters for s- and p-polarization are equally important. In order to reduce stray light, it is necessary to design non-polarizing thin film edge filters for color separation and recombination system in projectors. The novel design method is based on a broad-band Fabry–Perot interference filter in which both sides of transmittance band can be used as initial designs for long-wave-pass filter or short-wave-pass filters, and through suitable refinement to reduce the transmittance ripples, it is possible to achieve zero separation between two polarization components.     

Face mask detection using YOLOv3 and faster R-CNN models: COVID-19 environment

There are many solutions to prevent the spread of the COVID-19 virus and one of the most effective solutions is wearing a face mask. Almost everyone is wearing face masks at all times in public places during the coronavirus pandemic. This encourages us to explore face mask detection technology to monitor people wearing masks in public places. Most recent and advanced face mask detection approaches are designed using deep learning. In this article, two state-of-the-art object detection models, namely, YOLOv3 and faster R-CNN are used to achieve this task. The authors have trained both the models on a dataset that consists of images of people of two categories that are with and without face masks. This work proposes a technique that will draw bounding boxes (red or green) around the faces of people, based on whether a person is wearing a mask or not, and keeps the record of the ratio of people wearing face masks on the daily basis. The authors have also compared the performance of both the models i.e., their precision rate and inference time.

     

Applications of algebraic moments for edge detection for locally linear model

We describe a subpixel edge detection approach in images. The proposed approach is based on the algebraic moments of the brightness function of halftone images. For an ideal two-dimensional edge, we consider a model with the following four parameters: the edge orientation, the distance from the edge to the center of the mask, and the brightness values from both sides of the edge. To obtain all subpixel parameters of the edge, six algebraic moments are used. To compute the moments rapidly, masks are used. The specificity of the proposed approach is as follows: masks of almost all sizes can be used and they are computed by means of explicit relations provided in the present paper as well. Increasing mask sizes, one can increase the accuracy of the detection of subpixel edge parameters, which is especially important for high-definition images. We present experiments displaying the efficiency of the proposed approach.     

Dispersive refraction in ray tracing

Dispersive refraction is the property that gives gemstones their fire, and that makes prisms produce a spectrum from white light. Modeling disperison in a ray tracing environment requires solution of some new problems, but allows production of more exciting images. The mechanism of dispersive refraction is discussed, and its implementation is described. Pictures of a prism and of several diamonds are included. Images generated by this technique are realistic, but are computationally expensive.This work was supported in part by the National Science Foundation (DCR-8341796 and MCS-8121750), the Defense Advanced Research Projects Agency (DAAK11-84-K-0017), and the Office of Naval Research (N00014-82-K-0351). All opinions, findings, conclusions or recommendations expressed in this document are those of the author and do not necessarily reflect the views of the sponsoring agencies     

Structure quality in deep X-ray lithography applying commercial polyimide-based masks

The structure quality of deep X-ray lithography components strongly depends on the quality of the applied X-ray mask. In this article we compare the results obtained with two different mask types. Sophisticated working masks generated by e-beam lithography, soft X-ray lithography and electroplating of gold absorbers on a titanium mask membrane have been fabricated at the Institute for Microstructure Technology, Research Center, Karlsruhe (FZK/IMT), Germany. Prototype masks generated by e-beam lithography, optical lithography and electroplating of gold absorbers on a polyimide mask membrane have been fabricated by Optnics Precision, Japan, with the aim to offer commercially available low cost masks. Both mask types were applied to pattern PMMA resist layers of 300–750 μm thickness at the 2.5 GeV electron storage ring ANKA, Germany, using comparable process parameters. FZK/IMT masks provide microstructures with significantly better structure quality. The layout area, however, is currently limited to 12 cm², and the Ti mask membrane tends to lead to a slight resist surface attack, such as rounding of the resist edges. Optnics masks provide microstructures with reduced structure quality due to sidewall striations (sidewall roughness up to 2 μm) and thermal distortions (of up to 3–5 μm) which limit the potential scope of applications. They could nevertheless potentially be applied as low quality, low cost X-ray masks. High resolution and high accuracy applications, however, require more sophisticated but also more expensive masks, like the Ti-masks from FZK/IMT.     

Mask guided diverse face image synthesis

Recent studies have shown remarkable success in face image generation task. However, existing approaches have limited diversity, quality and controllability in generating results. To address these issues, we propose a novel end-to-end learning framework to generate diverse, realistic and controllable face images guided by face masks. The face mask provides a good geometric constraint for a face by specifying the size and location of different components of the face, such as eyes, nose and mouse. The framework consists of four components: style encoder, style decoder, generator and discriminator. The style encoder generates a style code which represents the style of the result face; the generator translate the input face mask into a real face based on the style code; the style decoder learns to reconstruct the style code from the generated face image; and the discriminator classifies an input face image as real or fake. With the style code, the proposed model can generate different face images matching the input face mask, and by manipulating the face mask, we can finely control the generated face image. We empirically demonstrate the effectiveness of our approach on mask guided face image synthesis task.     

Fabrication of HARM structures by deep-X-ray lithography using graphite mask technology

The cost-effective fabrication process for high-aspect-ratio microstructures using X-rays depends largely on the availability and quality of X-ray masks. The fabrication of X-ray masks using commercially available graphite sheet stock, as a mask membrane is one approach that is designed to reduce cost and turnaround time. Rigid graphite offers unique properties, such as moderate X-ray transmission, fairly low cost, electrical conductivity, and the ability to be used with either subtractive or additive processes [1, 2]. This paper will demonstrate the potential of a cost-effective, rapid prototyping of high-aspect-ratio microstructures (HARMs) using graphite masks. The graphite wafer accommodates both the intermediate mask and the working mask. In order to allow a direct comparison of the graphite mask quality with other X-ray masks, the primary pattern was derived from a Ti X-ray mask using soft X-ray lithography (XRL). Received: 7 July 1999 / Accepted: 29 September 1999     

A novel approach for multi-scale texture segmentation based on fractional differential

In this paper, we intend to implement multi-scale texture segmentation by fractional differential. We propose two fractional differential masks and present the structures and parameters of each mask, respectively, on eight directions. Moreover, by theoretical and experimental analysis, we find the better performance fractional differential mask. Finally, we further discuss the capability of fractional differential for multi-scale texture segmentation. Experiments show that, for rich-grained digital images, the capability for multi-scale texture segmentation by fractional differential-based approach appears efficient.     

A proposal for the modification of s‐CIELAB

The s‐CIELAB is a powerful tool in evaluating color reproduction errors in images. However, the formula is not yet completed, and a few refinements to the formula will enhance the accuracy of this tool. From a simple simulation, a black‐and‐white pattern causes unexpected false color components when using the s‐CIELAB formula. We show how these false color components are obtained with this formula. The main reason is a combination of components from different lowpass filters (LPFs). We show a method that improves this situation by introducing new psychological values and propose a modification to the formula employed by s‐CIELAB. The new formula is compatible with the psychological values L*u*v*, and a simulation with general images shows that the new method does not cause any false color components.     

一种新的基于MSRCR光照补偿算法

对质量较差的人脸图像进行光照补偿,多尺度Retinex算法是传统的算法中比较有效的一种,但是Retinex算法处理的人脸图像会产生"泛白、颜色失真、对比度低"现象,为了提高人脸识别率,为此提出了一种新的带色彩恢复的多尺度Retinex算法(MSRCR)对彩色图像进行光照补偿.在对MSRCR理论进行研究的基础上,对原有算法进行改进,使用了快速傅里叶变换,运行速度快于已有传统方法.经过实验证明,改进算法使图像的对比度,亮度,隐藏的细节等方面都有很大的增强.论述了该算法的原理和实现方法,同时通过实验将其与直方图均衡,Gamma变换等方法进行比较.实验结果表明:该算法对彩色图像光照补偿有很好的效果.     

基于黄金分割率的指纹图像方向滤波模板

设计一组方向滤波器,该滤波器包含8个方向的滤波器模板。将水平方向滤波模板中可能发生旋转溢出的位置赋零值,其位置参数值按照由中心向外围参数逐渐衰减的规律由一段基于黄金分割率的斐波那契数列段确定,其余7个方向的滤波模板由水平方向滤波模板旋转得到。在保证各个方向滤波器模板结构一致性的同时,既解决模板旋转溢出的问题,又使参数在对应方向上分布更具规律性。实验结果表明,该组方向滤波器模板对低质量指纹图像具有明显的增强效果,能更好地连接断裂脊线并分离粘连脊线。     

New fabrication techniques of SU-8 fiber holder with cantilever-type elastic microclips by inclined UV lithography in water using single Mylar mask

In contact UV lithography, a pair of cantilever beams fabricated by two inclined exposures at ±45° in SU-8 using a single mask will form a connected end on the top of SU-8 layer. These beams made of SU-8 with fixed-end have been used as optical fiber holders (Ling and Lian in Microsyst Technol 13(3–4):245–251, 2007). Recently, a two-mask, two-step process to fabricate free-end cantilever beams from SU-8 using inclined UV lithography has been developed (Ling et al. in Microsyst Technol 15(3):429–435, 2009), which has been successfully applied to fabricate SU-8 optical fiber holders with long free-end cantilever beams. In this process, two masks are needed in order to obtain free-end beams and the alignment between two exposures is always time consuming with limited accuracy. Two new techniques, inclined UV shadow mask lithography and inclined UV proximity lithography, have been illustrated here for fabricating free-end SU-8 cantilever beams, which eliminate the precise alignment step required in our previous work (Ling et al. in Microsyst Technol 15(3):429–435, 2009). In the inclined UV shadow mask lithography approach, the SU-8 cantilever beams without connected ends are formed by using one main mask and two shadow masks. Each shadow mask is used to selectively transfer one of the two separated patterns on main mask into SU-8 layer at +45° and −45°, respectively. In the inclined UV proximity lithography approach, a proper proximity gap between mask and SU-8 surface is obtained by using a 50 μm thick Mylar sheet, so that the exposing light paths that formed connected beam ends will fall inside the proximity layer instead of the SU-8. In this way, the desired open-end cantilever structures can be achieved. In this paper, the principles and the fabrication procedures of the proposed techniques are demonstrated and the preliminary results are discussed.     

Visual Enhancement of Underwater Images Using Transmission Estimation and Multi-Scale Fusion

The demand for the exploration of ocean resources is increasing exponentially. Underwater image data plays a significant role in many research areas. Despite this, the visual quality of underwater images is degraded because of two main factors namely, backscattering and attenuation. Therefore, visual enhancement has become an essential process to recover the required data from the images. Many algorithms had been proposed in a decade for improving the quality of images. This paper aims to propose a single image enhancement technique without the use of any external datasets. For that, the degraded images are subjected to two main processes namely, color correction and image fusion. Initially, veiling light and transmission light is estimated to find the color required for correction. Veiling light refers to unwanted light, whereas transmission light refers to the required light for color correction. These estimated outputs are applied in the scene recovery equation. The image obtained from color correction is subjected to a fusion process where the image is categorized into two versions and applied to white balance and contrast enhancement techniques. The resultants are divided into three weight maps namely, luminance, saliency, chromaticity and fused using the Laplacian pyramid. The results obtained are graphically compared with their input data using RGB Histogram plot. Finally, image quality is measured and tabulated using underwater image quality measures.     

Underwater image enhancement by maximum-likelihood based adaptive color correction and robust scattering removal

Underwater images often exhibit severe color deviations and degraded visibility, which limits many practical applications in ocean engineering. Although extensive research has been conducted into underwater image enhancement, little of which demonstrates the significant robustness and generalization for diverse real-world underwater scenes. In this paper, we propose an adaptive color correction algorithm based on the maximum likelihood estimation of Gaussian parameters, which effectively removes color casts of a variety of underwater images. A novel algorithm using weighted combination of gradient maps in HSV color space and absolute difference of intensity for accurate background light estimation is proposed, which circumvents the influence of white or bright regions that challenges existing physical model-based methods. To enhance contrast of resultant images, a piece-wise affine transform is applied to the transmission map estimated via background light differential. Finally, with the estimated background light and transmission map, the scene radiance is recovered by addressing an inverse problem of image formation model. Extensive experiments reveal that our results are characterized by natural appearance and genuine color, and our method achieves competitive performance with the state-of-the-art methods in terms of objective evaluation metrics, which further validates the better robustness and higher generalization ability of our enhancement model.     

Underdetermined Convolutive Blind Source Separation via Time–Frequency Masking

In this paper, we consider the problem of separation of unknown number of sources from their underdetermined convolutive mixtures via time-frequency (TF) masking. We propose two algorithms, one for the estimation of the masks which are to be applied to the mixture in the TF domain for the separation of signals in the frequency domain, and the other for solving the permutation problem. The algorithm for mask estimation is based on the concept of angles in complex vector space. Unlike the previously reported methods, the algorithm does not require any estimation of the mixing matrix or the source positions for mask estimation. The algorithm clusters the mixture samples in the TF domain based on the Hermitian angle between the sample vector and a reference vector using the well known k -means or fuzzy c -means clustering algorithms. The membership functions so obtained from the clustering algorithms are directly used as the masks. The algorithm for solving the permutation problem clusters the estimated masks by using k-means clustering of small groups of nearby masks with overlap. The effectiveness of the algorithm in separating the sources, including collinear sources, from their underdetermined convolutive mixtures obtained in a real room environment, is demonstrated.     

多尺度宽线检测方法

针对基于非线性滤波的宽线算子的不足,提出了一种多尺度宽线检测方法。基本宽线检测算子采用单个尺度模板检测图像中的宽线,导致仅能检测宽度小于模板半径的宽线特征,且在多条宽线交叉处检测效果较差;与之不同,多尺度宽线检测方法首先采用多个不同尺度的模板进行检测,然后在多个尺度归一化的检测结果中取最大响应值,再通过阈值分割、滤波处理等后处理步骤得到最终的检测结果。分别利用仿真图像和实际图像对多尺度宽线算子进行了性能测试,实验结果表明,多尺度宽线检测方法克服了基本宽线算子的不足,较好地检测出了图像中的宽线特征。     

Physical and statistical approaches for cloud identification using Meteosat Second Generation-Spinning Enhanced Visible and Infrared Imager Data

In this paper a cloud detection algorithm applied to the MSG-SEVIRI (Meteosat Second Generation-Spinning Enhanced Visible and Infrared Imager) data is described. In order to obtain a good performance in cloud detection, physical, statistical and temporal approaches have been used. In the statistical algorithm, the spectral and textural features of the MSG-SEVIRI images have been used as input, while, in the physical tests, a set of dynamic thresholds has been used. The physical algorithm does not use real time ancillary data— such as sea surface temperature map and NWP temperature and humidity profiles. A further test is applied to that pixels having low confidence to be clear or cloudy. This test takes advantage of the best MSG-SEVIRI temporal resolution and it applies the K-Nearest Neighbour classifier to the spectral and textural features calculated in “temporal” boxes 3 × 3 pixels, defined “temporal” because their elements belong to three subsequent MSG-SEVIRI images. The MACSP (cloud MAsk Coupling of Statistical and Physical methods) algorithm has been validated against the MODIS cloud mask and compared with CPR (Cloud Profiling Radar) and SAFNWC cloud masks. The outcomes show that the MACSP detects 91.8% of the total number of the pixels used for validation against MODIS cloud mask correctly, while the SAFNWC cloud mask detects 89.2% of them correctly. In particular, the MACSP classifies as cloudy 8.8% of the pixels classified by the MODIS cloud mask as clear, while the SAFNWC cloud mask classifies as cloudy 12.1% of them. The MACSP detects 91.2% of the cloudy CPR pixels and 90.8% of the cloud-free CPR pixels, considered for comparison, correctly. On the other hand, the SAFNWC and CPR cloud masks agree in the detection of 90.7% of the cloudy pixels and of 90.2% of the cloud-free pixels.     

Full‐color AMOLED with RGBW pixel pattern

Abstract— A full‐color AMOLED display with an RGBW color filter pattern has been fabricated. Displays with this format require about one‐half the power of analogous RGB displays. RGBW and RGB 2.16‐in.‐diagonal displays with average power consumptions of 180 and 340 mW, respectively, were characterized for a set of standard digital still camera images at a luminance of 100 cd/m². In both cases, a white‐emitting AMOLED was used as the light source, and standard LCD filters were used to provide the R, G, and B emission. The color gamuts of these displays were identical and the higher overall efficiency of the RGBW format results from two factors. First, a large fraction of a typical image is near neutral in color and can be reproduced using the white sub‐pixel. Second, the white sub‐pixel in an RGBW AMOLED display is highly efficient because of the absence of any color filter. The efficiency of these displays can be further enhanced by choosing a white emitter optimized to the target display white point (in this case D65). A two‐emission layer configuration based upon separate yellow and blue‐emitting regions is shown to be well suited for both the RGBW and RGB formats.     

A monolithic segmented functional light guide for 2‐D dimming LCD backlight

Abstract— An edge‐lit backlight with a thin structure and 2‐D dimming function is a highlighted requirement. To achieve a thin backlight unit for 2‐D dimmable displays, a monolithic functional light‐guide plate (LGP) was segmented by using a recessed U‐groove with graded height as semi‐partitions. The height of the U‐groove controls the cross‐talk between the segments. A single segment was characterized with an array of louver‐shaped micro‐prisms that function as unilateral reflectors for light distributing, directing, and extracting. Arrays of rounded micro‐prisms, and lenticular prisms for in‐ and out‐coupling, are designed on the light injection surface and front surface of the LGP for light‐cone shaping on the BLU. The light guide has a length of 73.0 mm, a width of 40.7 mm, and a thickness of 0.7 mm. The LGP was segmented into 16 segments where the width and graded height of the recessed U‐prism between the segments is 0.020 mm and 0.10–0.50 mm, respectively. By using the monolithic light‐guide plate, the cross‐talk is suppressed to 20% and 4% at the center of first and second neighboring segments, respectively.     

一种用于单CCD图像传感器的图像插值算法

由于物理结构的限制,单CCD图像传感器在每个像素位置上只能采集一个颜色分量,其余两个颜色分量只能通过插值的办法得到。提出一种在色差空间进行插值的算法,利用具有比例线性关系的局部颜色特性和局部协方差求得最小均方误差意义下的最优插值系数。所获取的该插值系数具有边缘细节保持性,同时色差空间的插值又考虑了不同颜色分量间的耦合性,因而有效地抑制了图像边缘的模糊和颜色失真。实验结果表明,该算法可获得高质量的插值图像。