图像相减的一种新模型

借用光学滤波系统理论,对对称图像相减的数学模型进行推广,得出了傅里叶变换实现非对称放置两个图像相减的数学表达式,诠释了其物理意义,规范了其适用范围和使用条件。计算机模拟实验验证了结论的可靠性与可行性。该结论对信息处理、图像识别等具有实用价值。     

一种利用光栅编码实现实时光学图像相减的新方法

介绍一种利用光栅编码实现实时光学图像相减的新方法。仅使用一块一维透反光栅就可完成对待相减的两幅图像进行编码，再通过傅里叶滤波进行解码，即可实时完成光学图像的复振幅相减。文中给出了原理分析及其实验结果，最后作了简要的讨论。     

基于三维图像快速分层滤波的聚焦梯度模拟方法

基于透镜成像模型推导出模糊函数σ与物距及透镜焦距的关系．采用对深度三维图像自适应分层滤波方法，引入差异度函数，按差异度函数把深度图像分解成Ｋ个ｚ方向上不相交的子图像，通过对子图像的滤波合成，降低算法的复杂度，并使滤波后的误差控制在给定范围内，引入ａｌｐｈａ值、按层合成等手段解决滤波后的遮挡及边界问题．为计算机渲染（ｒｅｎｄｅｒ）算法提供了一种新的后期处理途径     

尺度估计和多特征融合的目标跟踪算法研究

针对核相关滤波器跟踪算法(Kernel Correlation Filter,KCF)在特征提取单一以及尺度估计不足而导致跟踪效果不佳的问题,本文提出了一种多特征融合的尺度自适应核相关滤波目标跟踪算法.首先,使用帧差法将相邻帧图像对应像素值相减得到差分图像;其次,提取差分图像的方向直方图特征,与目标的均一局部二值纹理特...     

采用小波变换和数学形态学的小目标检测

鉴于常用检测方法不能准确稳定地检测出复杂背景中小目标,结合小波变换和数学形态学,提出了一种小目标检测新方法.首先对图像进行单尺度小波变换,提取高频分量系数;其次,利用阈值算法将各个高频分量系数图像转化为二值图像后对其进行多结构元素形态学滤波,滤波结果与原二值图像相减后在差值图像上得到可能的小目标.将3个方向的高频系数的检测结果相关联获得单帧检测结果;最后将多个单帧检测结果进行流水线检测,得到最终的检测结果.仿真结果表明该方法能够准确稳定地检测出信噪比(SNR)大于2的弱小目标.     

红外背景抑制与点目标分割检测算法研究

针对红外点目标检测问题,采用图像灰度同本行均值相减方法抑制温度场的非线性影响;利用Top-Hat算子形态滤波,抑制背景和增强目标;通过比较预处理后的不同背景下红外图像直方图特点,确定分割阈值;最后进行目标二值化分割,得到包含较少虚警点的点目标分割图像.实验证明,该方法较好地解决了不同红外背景下低信噪比红外点目标的分割检测问题.     

海空背景下红外点目标检测算法

提出了一种基于灰度形态学的海空背景下的红外点目标检测算法。该算法三步：第一步,对原始序列图像进行了膨胀后累加,以提高信噪比（SNR）;第二步,对原始序列图像进行形态学滤波,去掉噪声和目标以提取出背景;第三步,前两步结果相减,自适应阈值后即可得到点目标,用实际摄取的图像进行实验,结果表明该算法能检测出信杂比（SCR0为1的红外图像。     

一种改进的中值滤波方法及其在自聚焦透镜端面图像特征提取中的应用

针对自聚焦透镜端面图像的特点,本文提出了一种改进型中值滤波方法,并应用该方法进行了图像缺陷特征的提取实验。文中详细介绍了改进中值滤波方法的基本原理,包括模板取值规则、位置设定及比较试验结果。另外,给出了实验装置的构成及原理,针对自聚焦透镜表面缺陷所进行的一系列的图像处理实验,包括阈值分割及缺陷形态学统计等,实验结果证明了该方法的有效性。     

基于边缘增强引导滤波的光场全聚焦图像融合

受光场相机微透镜几何标定精度的影响,4D光场在角度方向上的解码误差会造成积分后的重聚焦图像边缘信息损失,从而降低全聚焦图像融合的精度。该文提出一种基于边缘增强引导滤波的光场全聚焦图像融合算法,通过对光场数字重聚焦得到的多幅重聚焦图像进行多尺度分解、特征层决策图引导滤波优化来获得最终全聚焦图像。与传统融合算法相比,该方法对4D光场标定误差带来的边缘信息损失进行了补偿,在重聚焦图像多尺度分解过程中增加了边缘层的提取来实现图像高频信息增强,并建立多尺度图像评价模型实现边缘层引导滤波参数优化,可获得更高质量的光场全聚焦图像。实验结果表明,在不明显降低融合图像与原始图像相似性的前提下,该方法可有效提高全聚焦图像的边缘强度和感知清晰度。     

基于远心光学系统散焦图像的距离估计

基于远心光学系统散焦图像的距离估计的方法是用CCD摄取两幅散焦程度不同的图像,通过不同的散焦度,计算得到图像的距离信息.为减少放大率的变化对试验结果的影响,在距CCD透镜距离为焦距处加一个光阑构成一个远心透镜.这种方法的关键是求两幅图像的散焦值,本文采用最小二乘法来求散焦值.     

Flip visual cryptography (FVC) with perfect security,conditionally-optimal contrast,and no expansion

This paper proposes a flip visual cryptography (FVC) scheme with perfect security, conditionally optimal contrast, and no expansion of size. The proposed FVC scheme encodes two secret images into two dual-purpose transparencies. Stacking the two transparencies can reveal one secret image. Flipping one of the two transparencies and then stacking with the other transparency can reveal the second secret image. The proposed scheme is proved to have conditionally optimal contrast: its contrast is optimal if the double-secrets non-expanded FVC scheme is required to have perfect security. The perfect security is also proved.     

Halftone visual cryptography.

Visual cryptography encodes a secret binary image (SI) into n shares of random binary patterns. If the shares are xeroxed onto transparencies, the secret image can be visually decoded by superimposing a qualified subset of transparencies, but no secret information can be obtained from the superposition of a forbidden subset. The binary patterns of the n shares, however, have no visual meaning and hinder the objectives of visual cryptography. Extended visual cryptography [1] was proposed recently to construct meaningful binary images as shares using hypergraph colourings, but the visual quality is poor. In this paper, a novel technique named halftone visual cryptography is proposed to achieve visual cryptography via halftoning. Based on the blue-noise dithering principles, the proposed method utilizes the void and cluster algorithm [2] to encode a secret binary image into n halftone shares (images) carrying significant visual information. The simulation shows that the visual quality of the obtained halftone shares are observably better than that attained by any available visual cryptography method known to date.     

Cheating Prevention in Visual Cryptography

Visual cryptography (VC) is a method of encrypting a secret image into shares such that stacking a sufficient number of shares reveals the secret image. Shares are usually presented in transparencies. Each participant holds a transparency. Most of the previous research work on VC focuses on improving two parameters: pixel expansion and contrast. In this paper, we studied the cheating problem in VC and extended VC. We considered the attacks of malicious adversaries who may deviate from the scheme in any way. We presented three cheating methods and applied them on attacking existent VC or extended VC schemes. We improved one cheat-preventing scheme. We proposed a generic method that converts a VCS to another VCS that has the property of cheating prevention. The overhead of the conversion is near optimal in both contrast degression and pixel expansion     

Comment on "Cheating prevention in visual cryptography"

Visual cryptography (VC), proposed by Naor and Shamir, has numerous applications, including visual authentication and identification, steganography, and image encryption. In 2006, Horng showed that cheating is possible in VC, where some participants can deceive the remaining participants by forged transparencies. Since then, designing cheating-prevention visual secret-sharing (CPVSS) schemes has been studied by many researchers. In this paper, we cryptanalyze the Hu-Tzeng CPVSS scheme and show that it is not cheating immune. We also outline an improvement that helps to overcome the problem.     

Analysis of Multiple Orientations

Estimation of local orientations in multivariate signals is an important problem in image processing and computer vision. This general problem formulation also covers optical flow estimation, which can be regarded as orientation estimation in space-time-volumes. Modelling a signal using only a single orientation, however, is often too restrictive, since occlusions and transparencies occur frequently, thus necessitating the modelling and analysis of multiple orientations. We, therefore, develop a unifying mathematical model for multiple orientations: Beyond describing an arbitrary number of orientations in scalar- and vector-valued image data such as color image sequences, it allows the unified treatment of additively and occludingly superimposed oriented structures as well as of combinations of these. Based on this model, we describe estimation schemes for an arbitrary number of additively or occludingly superimposed orientations in images. We confirm the performance of our framework on both synthetic and real image data.     

9A5--Wide field active imaging

In this paper we report the results of some experiments in active imaging-image processing in which the pictorial information is placed within the laser cavity. By the use of an active medium which provides high gain over a wide aperture, in conjunction with a highly degenerate conjugate resonator, we have been able to obtain diffraction limited resolution with an information content orders of magnitude greater than previously reported. The resonator used is the Flat-Field Conjugate Resonator (FFCR), which can support as many as 10⁷modes of nearly equalQwhen properly designed lenses are used. As active medium we used the pulsed hollow cathode Hg⁺laser. In the present FFCR, two plane mirrors are imaged one upon the other by means of two achromatic doublets (focal lengths about 200 mm) located between the ends of the discharge tube and the mirrors. Active imaging is accomplished by masking one of the mirrors and observing the pattern resulting on the other mirror. Masks used include pinholes, wire meshes, and photographic transparencies as well as patterns etched in thin metallic films that were used directly as mirrors. With the doublets working nearf/10, the resolution over a 15mm diameter field was greater than 100 lines/mm, which corresponds quite well to the observed resolution of the passive system. The resonator was thus capable of actively imaging photographic transparencies having more than 10⁶bits. One characteristic of active imaging in this type of resonator is that all the modes have a large common active volume, and the suppression of some of the modes enhances the intensity of the others. Furthermore, the nonlinear behavior of a laser as an oscillator allows sharp discrimination between differing loss levels in the cavity. These effects have been observed, and their possible application to contrast enhancement and image dissection is discussed.     

遥操作系统透明性的量化分析

针对基于波变量法的遥操作系统,研究了其透明性的量化分析方法.利用Yokokohji透明性指数研究了系统在不同控制策略、时延和环境下的透明性,以确切数值的形式给出了系统透明性,并给出了系统透明性的量化分析对比结果.实验结果对于系统在不同状况下,控制方法和控制参数的选择有着一定的参考价值.     

On the Contrast in Visual Cryptography Schemes

A visual cryptography scheme is a method to encode a secret image SI into shadow images called shares such that certain qualified subsets of shares enable the ``visual' recovery of the secret image. The ``visual' recovery consists of xeroxing the shares onto transparencies, and then stacking them. The shares of a qualified set will reveal the secret image without any cryptographic computation. In this paper we analyze the contrast of the reconstructed image in k out of n visual cryptography schemes. (In such a scheme any k shares will reveal the image, but no set of k-1 shares gives any information about the image.) In the case of 2 out of n threshold schemes we give a complete characterization of schemes having optimal contrast and minimum pixel expansion in terms of certain balanced incomplete block designs. In the case of k out of n threshold schemes with we obtain upper and lower bounds on the optimal contrast. Received 27 September 1996 and revised 13 February 1998     

On Increasing the Switching Rate in a Single-Domain Magnetooptic Cell

A single-domain cell for magnetooptic controlled transparencies that improves their speed is suggested.