常用光线下立体落影的画法研究

指出了传统的求立体,尤其是曲面立体的落影方法的困难,提出了一种新的求立体落影的方法.充分利用AutoCAD的二维图形编辑功能以及与AutoLISP语言的接口功能,并在数学分析的基础上与程序设计有机地结合起来,将简单平面立体落影的拉伸画法引伸到圆的落影画法,从而实现了对复杂回转曲面体落影的作图.该方法简单,易于掌握.     

Shadow removal from image of stained glass windows

Shadows may be formed on stained glass windows by structural bars supporting the leaded panels, or by external protective wire grilles, or by masonry, such as mullions or buttresses, or external objects, such as trees. The eye tends to “discount” such shadow formations when viewing the actual windows even though in the photographic images they are very clearly visible. This article introduces a method to remove shadow effects on stained‐glass windows; the observed image, as captured by the camera, may be modeled mathematically as a combination of a “true stained glass image” and a “grille/bar image.” A mixture model is derived, based on a theoretical model of image formation, leading to a conjectured relationship between “shadow” pixels and the neighboring “nonshadow” pixels. The resulting mixture model assumes a multiplicative relationship. If this mixture can be separated into its original components, then it should be possible to remove the unwanted shadow component from the captured image to produce the desired image of the stained glass without the shadows. The digital modeling techniques enable the shadows to be characterized and removed with a reasonable degree of success. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 223–226, 2010.     

Overlapping Shadow Rendering for Outdoor Augmented Reality

Realism rendering methods of outdoor augmented reality (AR) is an interesting topic. Realism items in outdoor AR need advanced impacts like shadows, sunshine, and relations between unreal items. A few realistic rendering approaches were built to overcome this issue. Several of these approaches are not dealt with real-time rendering. However, the issue remains an active research topic, especially in outdoor rendering. This paper introduces a new approach to accomplish reality real-time outdoor rendering by considering the relation between items in AR regarding shadows in any place during daylight. The proposed method includes three principal stages that cover various outdoor AR rendering challenges. First, real shadow recognition was generated considering the sun’s location and the intensity of the shadow. The second step involves real shadow protection. Finally, we introduced a shadow production algorithm technique and shades through its impacts on unreal items in the AR. The selected approach’s target is providing a fast shadow recognition technique without affecting the system’s accuracy. It achieved an average accuracy of 95.1% and an area under the curve (AUC) of 92.5%. The outputs demonstrated that the proposed approach had enhanced the reality of outside AR rendering. The results of the proposed method outperformed other state-of-the-art rendering shadow techniques’ outcomes.     

Mach bands and airplane shadows cast on dry terrain

Luminous rings are often seen surrounding the shadow of a high-flying airplane. Some of these phenomena are due to water droplets (glories, the Heiligenschein), but a different sort of explanation is required when a luminous ring (sometimes simply a bright spot) is seen while the plane is flying over dry terrain. Demonstrations involving distances and shadows manyfold smaller than those of an airliner's shadow show that Mach bands can produce illusory luminance phenomena that greatly resemble those associated with a plane's shadow over dry terrain. Luminance rings have recently also been observed over dry, sparsely vegetated terrain, around the shadow of an adjacent airplane (i.e., far from the observer's antisolar point), thereby excluding all previous alternative interpretations; Mach bands are thus a likely explanation for at least some instances of dry-terrain luminous rings around airplane shadows.     

一种新的多特性联合阴影检测方法

针对运动阴影检测时单一阴影特征难以完全将前景和阴影正确分离,提出一种多特征联合运动阴影检测方法.考虑运动阴影的光照、色度、纹理和区域统计特性,提出采用小邻域光照的对数比值不变性来判定阴影,接着联合阴影HSV颜色空间特性和梯度方向小块合并的阴影区域统计特性来实现多特征联合运动阴影检测.为了客观评价方法性能,采用一种改进的量化方法,对不同光照和环境条件下的视频序列进行测试.实验结果表明,该方法效果好,前景检测率和阴影检测率高,可应用于智能视频监控的目标检测.     

Shadow Detection and Removal From Photo-Realistic Synthetic Urban Image Using Deep Learning

Recently, virtual reality technology that can interact with various data is used for urban design and analysis. Reality, one of the most important elements in virtual reality technology, means visual expression so that a person can experience threedimensional space like reality. To obtain this realism, real-world data are used in the various fields. For example, in order to increase the realism of 3D modeled building textures real aerial images are utilized in 3D modelling. However, the aerial image captured during the day can be shadowed by the sun and it can cause the distortion or deterioration of image. To resolve this problem, researches on detecting and removing shadows have been conducted, but the detecting and removing shadow is still considered as a challenging problem. In this paper, we propose a novel method for detecting and removing shadows using deep learning. For this work, we first a build a new dataset of photo-realistic synthetic urban data based on the virtual environment using 3D spatial information provided by VWORLD. For detecting and removing shadow from the dataset, firstly, the 1-channel shadow mask image is inferred from the 3-channel shadow image through the CNN. Then, to generate a shadow-free image, a 3-channel shadow image and a detected 1-channel shadow mask into the GAN is executed. From the experiments, we can prove that the proposed method outperforms the existing methods in detecting and removing shadow.     

Extinction of light in Brewster polarizers: a shadowlike phenomenon

A Brewster polarizer in this study is any dielectric plane reflecting surface reflecting light at or near the Brewster angle of incidence. In this paper, we consider an interesting phenomenon observed when we use an extended source of light or a cone of light with its axis incident on the plane surface at the Brewster angle. The resulting reflected light is viewed (a) through an ordinary sheet polarizer and (b) after reflection from another Brewster polarizer. The extinction pattern of light by such a system is in the form of an elongated black shadow in (a) and a nearly circular shadow in (b), respectively. These shadows are explained on the basis and use of the familiar Fresnel equations at a plane interface between two dielectric media. Photographs of the shadows are also presented.     

Micro 3D measurement method using SEM

Three diamensional (3D) measurement method by Scanning Electron Microscope (SEM) has already been proposed by using the principle of shadow moiré. In the method, the image of original grid in shadow moiré image must be clearly removed in fringe analysis process in order to perform high resolution analysis. A new method based on the principle of projection moiré is proposed to solve the trouble concerning the grid. In this paper, the mechanism of producing some shadows of grid on the surface of the object by back scattering electron beam in the new method is discussed. Fringe image as shadow of grid is analyzed by Wavelet transform. The precise 3D measurement is realized by using the phenomenon of shadows of grid. Furthermore, a 3D micro structure on the head of a hard disk is measured. From the comparison of results obtained by Atomic Force Microscope (AFM), it is confirmed that the proposed method has high-resolution power(about 20nm).     

Instantaneous velocity displacement and contour measurement by use of shadow moiré and temporal wavelet analysis

A temporal wavelet analysis method is proposed for velocity, displacement, and three-dimensional surface-profile measurement of a continuously deforming object by use of the shadow moiré technique. A grating is placed close to a deforming object, and its shadow is observed through the grating. The moiré fringe patterns, generated by the interference of the grating lines and their shadows, are captured by a high-speed CCD camera with a telecentric gauging lens. Instantaneous frequency of gray-value variation is evaluated point by point with the continuous wavelet transform. From the instantaneous frequency of each point on the object, the velocity, displacement, and high-quality surface profile at different instants can be retrieved. In this application, two specimens are tested to demonstrate the validity of the proposed method: One is a small coin with a rigid body motion, and the other is a simply supported beam subjected to a central point load. The results are compared with those obtained from temporal Fourier-transform and mechanical stylus methods.     

Blue shadows: physical, physiological, and psychological causes

The apparent blueness of outdoor shadows has two main causes: the illumination of the shadows by blue skylight and the enhancement of the perception of blue by simultaneous color contrast. Other physiological mechanisms, such as brightness contrast and afterimages, can also affect the perception of a shadow's blueness. Preferential scattering by the cornea does not seem to make a major contribution. Despite these effects, color constancy causes most people to observe an empirically blue shadow as colorless.     

A framework for moving object segmentation using dynamic background modelling and shadow suppression in complex wavelet domain

In this paper, a framework for dynamic background modelling and shadow suppression under rapidly changing illumination conditions for moving object segmentation in complex wavelet domain is proposed which deals with the problems of ghosts, object shadows, noise, object distortion in dynamic background changes. The proposed method consists of eight steps applied on given video frames which include: wavelet de-composition of frame using complex wavelet transform; use of change detection on detail coefficients; use of dynamic background modelling on approximate co-efficient; cast shadow suppression; use of soft thresholding for noise removal; strong edge detection; inverse wavelet transformation for reconstruction and finally using closing morphology operator. A comparative analysis of the proposed method is presented both qualitatively and quantitatively with other standard methods available in the literature for four datasets in terms of various performance measures. Experimental results demonstrate the efficacy of the proposed method is better in terms of relative foreground area measure, misclassification penalty, relative position based measure, normalised cross-correlation, normalised absolute error, peak signal-to-noise ratio and pixel classification based measure as compared to other standard methods.     

Improved Multileader Optimization with Shadow Encryption for Medical Images in IoT Environment

Nowadays, security plays an important role in Internet of Things (IoT) environment especially in medical services’ domains like disease prediction and medical data storage. In healthcare sector, huge volumes of data are generated on a daily basis, owing to the involvement of advanced health care devices. In general terms, health care images are highly sensitive to alterations due to which any modifications in its content can result in faulty diagnosis. At the same time, it is also significant to maintain the delicate contents of health care images during reconstruction stage. Therefore, an encryption system is required in order to raise the privacy and security of healthcare data by not leaking any sensitive data. The current study introduces Improved Multileader Optimization with Shadow Image Encryption for Medical Image Security (IMLOSIE-MIS) technique for IoT environment. The aim of the proposed IMLOSIE-MIS model is to accomplish security by generating shadows and encrypting them effectively. To do so, the presented IMLOSIE-MIS model initially generates a set of shadows for every input medical image. Besides, shadow image encryption process takes place with the help of Multileader Optimization (MLO) with Homomorphic Encryption (IMLO-HE) technique, where the optimal keys are generated with the help of MLO algorithm. On the receiver side, decryption process is initially carried out and shadow image reconstruction process is conducted. The experimentation analysis was carried out on medical images and the results inferred that the proposed IMLOSIE-MIS model is an excellent performer compared to other models. The comparison study outcomes demonstrate that IMLOSIE-MIS model is robust and offers high security in IoT-enabled healthcare environment.     

What shadows reveal about object structure

In a scene observed from a fixed viewpoint, the set of shadow boundaries in an image changes as a point light source (nearby or at infinity) assumes different locations. We show that for any finite set of point light sources illuminating an object viewed under either orthographic or perspective projection, there is an equivalence class of object shapes having the same set of shadows. Members of this equivalence class differ by a four-parameter family of projective transformations, and the shadows of a transformed object are identical when the same transformation is applied to the light source locations. Under orthographic projection, this family is the generalized bas-relief (GBR) transformation, and we show that the GBR transformation is the only family of transformations of an object's shape for which the complete set of imaged shadows is identical. Finally, we show that given multiple images under differing and unknown light source directions, it is possible to reconstruct both an object's surface and the light source locations up to this family of transformations from the shadows alone.     

一种基于能量最小化的运动阴影检测方法

针对传统方法经常将运动阴影也检测为前景的问题,本文将检测问题表示为能量函数,通过最小化能量函数来检测运动阴影.这种方法先用传统的背景对消方法分别得到静态背景和含有真实前景和运动阴影的运动目标,然后在运动目标中,利用阴影的颜色不变性和纹理不变性,以及阴影和前景的时空一致性,构造出能量函数,最后通过最小化能量函数,将真实前景从运动目标中准确地分割出来,从而达到消除运动阴影的目的.我们在包含运动阴影的视频中,对本文方法进行测试,并和其它方法比较.实验结果表明,本文的方法无论在室内场景,还是在室外场景都可以很好地分割前景和阴影.     

基于纹理的运动阴影检测方法

针对在视频对象分割时,运动阴影常被误分为视频对象,给出一种新的运动阴影检测方法.首先,进行基于自适应高斯混合模型的背景提取,获得包含运动阴影的前景分割,然后根据灰度图像中阴影区域和已获取背景相应位置的纹理相似性,进行阴影检测.纹理采用局部二元图(Local Binary Patterns,LBP)统一模式的直方图表征.实验表明,方法检测效果好,速度快,可应用于运动目标检测分割及跟踪等领域.     

Spatio-temporal motion-based foreground segmentation and shadow suppression

A relevant problem in computer vision is how to detect and track moving objects from video sequences efficiently. Some algorithms require manual calibration in terms of specification of parameters or some hypotheses. A novel method is developed to extract moving objects through multi-scale wavelet transform across background subtraction. The optimal selection of threshold is automatically determined which does not require any complex supervised training or manual calibration. The proposed approach is efficient in detecting moving objects with low contrast against the background and the detection is less affected by the presence of moving objects in the scene. The developed method combines region connectivity with chromatic consistency to overcome the aperture problem. Ghosts are removed by the proposed background update function, which efficiently prevents undesired corruption of background model and does not consider adaptation coefficient. The mentioned approach is scene-independent and the capacity to extract moving object and suppress cast shadow is high. The developed algorithm is flexible and computationally cost-effective. Experiments show that the proposed approach is robust and efficient in segmenting foreground and suppressing shadow by comparison.     

一种新的模板匹配算法及其在三维形貌测量中的应用

投影光栅法是进行三维形貌测量的有效手段，但当被测物体陡峭度较大或存在高度突变时会出现阴影问题。为此本提出一种基于互相关函数差值的模板匹配算法，该算法可以有效地解决这一问题，同时该算法也可用于大尺度物体三维形貌测量的拼接技术，中给出了算法的详细描述及实例计算，计算结果证明了该算法的正确性。     

Separating reflections from images by use of independent component analysis.

The image of an object can vary dramatically, depending on lighting, specularities, reflections, and shadows. It is often advantageous to separate these incidental variations from the intrinsic aspects of an image. We describe a method for photographing objects behind glass and digitally removing the reflections from the surface of the glass, leaving the image of the objects behind the glass intact. We describe the details of this method, which employs simple optical techniques and independent component analysis and show its efficacy with several examples.     

Cryptanalysis of Chen et al.’s multi-secret visual cryptography scheme

Abstract

In a (k, n) visual cryptographic scheme (VCS), a secret image is encrypted into n shadow images in such way that any k or more shadows can be superimposed to visually decode the secret, and less than k shadows cannot obtain any information on the secret image. Most VCSs only share one secret image. A (k, n, s) multi-secret VCS (MVCS) is a (k, n)-VCS, which can share s secret images. Recently, Chen et al. introduced a novel (2, 2, 4)-MVCS. However, their scheme is insecure. The threshold property of Chen et al.’s (2, 2, 4)-MVCS is compromised. In this paper, we show how an attacker retrieves the secret information of Chen et al.’s (2, 2, 4)-MVCS from one shadow image.     

Ultrasonic edge shadowing around cylindrical cavities with and without walls

In B-mode ultrasound images, the speckle distal to the edges of cavities of contrasting speed of sound (SOS) can be imprinted with a pattern characteristic of the cavity. This pattern, termed edge shadowing, is likely to involve alteration of both the speckle amplitude and its correlation length. Using the acoustic field calculated from the exact solution to the wave equation, we have simulated the ensemble-averaged speckle amplitude in B-mode images of cylindrical cavities both with and without walls, and compared the results to a simpler ray-based model. The simulations show that edge shadowing is caused predominantly by contrasts of the SOS, rather than of the density. The shadows on both walled and wall-less cylinders, for a focused incident beam, grow darker as the magnitude of the SOS contrast increases over a range up to +/- 10%. Extra shadows, caused by the inner wall boundary, appear on images of walled cylinders. The ray-based model agrees well with the wave model except in the shadow regions, within which the complexity of the phenomena seems to require the wave model.