Edge enhancement of phase objects through complex media by using transmission-matrix-based spiral phase contrast imaging

The wavefront shaping based technique has been introduced to detect the edges of amplitude objects through complex media, but the extraction of the boundary information of invisible phase objects through complex media has not been demonstrated yet. Here, we present a phase contrast imaging technique to overcome the scattering, aiming to achieve the edge detection of the phase object through the complex media. An operator based on the experimentally measured transmission matrix is obtained by numerically adding a spiral phase in the Fourier domain. With the inverse of the filtered transmission matrix, we can directly reconstruct the edge enhanced images for both amplitude object and phase object beyond scattering. Experimentally, both digital and real objects are imaged, and the results verify that isotropic edge detection can be achieved with our technique. Our work could benefit the detection of invisible phase objects through complex media.     

Optical rotation invariant corner detector

In this work we introduce a new approach for corner extraction with rotation invariance. The method is based on an optical processor where the filter in the frequency plane is composed by a spiral phase function and a binary amplitude. The output image of the optical setup presents intensity peaks in each square corner location. The performance of the proposed method was tested on synthetic scenes by numerical simulations and by optical measurements. The presented results show that the method allows the corner extraction, even with rotated scenes.     

Identifying the Symmetry of an Object Based on Orbital Angular Momentum through a Few-Mode Fiber

In recent years, orbital angular momentum(OAM), as a new usable degree of freedom of photons, has been widely applied in both classical optics and quantum optics. For example, digital spiral imaging uses the OAM spectrum of the output beam from the object to restore the symmetry information of the object. However,the related experiments have been carried out in free space so far. Due to the poor anti-noise performance,limited transmission distance and other reasons, the practicability is seriously restricted. Here, we have carried out a digital spiral imaging experiment through a few-mode fiber, to achieve the identification of the symmetry of object by measuring the OAM spectrum of the output beam. In experiment, we have demonstrated the identification of the symmetry of amplitude-only and phase-only objects with the two-, three-and four-fold rotational symmetries. We also give the understanding of the physics. We believe that our work has greatly improved the practical application of digital spiral imaging in remote sensing.     

编码孔径成像:一种全息逆转滤波处理

本文利用动态范围宽的全息逆转滤波器(HIF)对几种编码图像进行了解码.讨论了HIF的性能,给出光学模拟下非冗余列阵(NRA)对二维物体成像和对三维物体层析的一些结果.     

Shadow effects in spiral phase contrast microscopy

Recently it has been demonstrated that spatial filtering of images in microscopy with a spiral phase element in a Fourier plane of the optical path results in a strong edge enhancement of object structures. In principle the operation is isotropic, i.e., all phase edges of a sample object are highlighted simultaneously, independent of their local direction. However, here we demonstrate that the symmetry can be broken intentionally by controlling the phase of the central area of a spiral phase hologram, which is displayed at a computer controlled spatial light modulator. This produces an apparent shadow effect which can be rotated at video rate. The resulting relieflike impression of the sample topography with a longitudinal resolution in the subwavelength regime is demonstrated by imaging a standard low contrast test sample consisting of a human cheek cell.     

Edge directional 2D LMS filter for infrared small target detection

In this paper, we introduce an edge directional 2D least mean squares (LMSs) filter for small target detection in infrared (IR) images. Generally, the 2D LMS filter functions as a background prediction to apply to IR small target detection field. In order to accurately predict background objects as well as regions covered by small targets, the proposed 2D LMS filter take full advantage of edge information of prediction pixels corresponding to surrounding blocks around current filter window. And, to adjust adaptively its step size in the background and small target region, the adaptive region-dependent nonlinear step size is calculated by using the variance of the prediction pixels of the surrounding blocks. This prediction structure and adaptive step size of the proposed 2D LMS filter is applied to the background region including objects such as cloud edge and small target region differently. Through this way, the proposed 2D LMS filter predicts the background excluding small targets. Then, by subtracting the predicted background from the original IR image, small targets can be extracted. Experimental results show that the proposed 2D LMS filter has stronger target extraction and better background suppression ability compared to the existing 2D LMS filters.     

Semiderivative real filter for microoptical elements quality control

The article presents a proposal for a new method of automatic quality control of microlenses arrays, which is based on a semiderivative real filter. The use of the semiderivative filter for examining pure-phase objects involves modifying the spatial frequency. The basis of the proposed setup is a 4f correlator setup with coherent light. The phase object examined is placed in the input plane of the correlator. Next, the light passes through a filter located in the frequency plane, which gives an intensity signal. In the output plane a charge-coupled device (CCD) camera registers the light intensity, the range of which informs the shape of the phase object. The proposed method is shift invariant, so it allows for examination of single elements or a set of micro-optical elements simultaneously. Additionally, the same setup allows for measuring the phase of objects whose thickness is either considerably smaller or much bigger than 2π.     

基于液晶空间光调制器的空间滤波实验

空间滤波实验可以实现对输入物体的频谱分析及图像的边缘增强、噪声消除等各种图像处理。液晶空间光调制器可以作为衍射波面变换器件来使用。在空间滤波实验系统的滤波面上放置了液晶空间光调制器,并用CCD数码相机进行输出图像的观察和记录,分别给出了低通滤波、高通滤波、方向滤波等的仿真实验结果。该实验实现了输入数字物体的实时改变,并能够实时观察采用不同空间滤波器对输出像的影响。     

一种融合边缘信息的面向对象遥感图像分割方法

针对高分辨率遥感图像边缘突出、上下文信息丰富等特点,提出一种融合边缘特征的区域分割算法,基于面向对象图像分析方法,综合考虑遥感图像的光谱和空间特征。首先应用SUSAN算子对全色波段图像提取边缘信息,然后对融合后的彩色图像进行两阶段分割,第一阶段采用倒四叉树融合成初始图像对象,在第二阶段中通过在区域异质性判据中增加边界强度特征的方式融合已提取的边缘信息进行分级区域合并,形成图像分割结果。文中用三峡库区某区域QuickBird数据进行了实验,并与ENVI Zoom和Definiens下的分割结果进行了效果对比和定量评价,结果表明该方法可行、有效。     

Resolution-enhanced 3D image correlator using computationally reconstructed integral images

In this paper, a novel resolution-enhanced three-dimensional (3D) image correlator using the computationally reconstructed integral images is proposed in order to extract target object’s 3D location data in a scene. Elemental images of the reference and target objects are picked up by lenslet arrays and using these elemental images, reference and target plane images are reconstructed on the output plane by means of a modified computational integral imaging reconstruction technique. Then, through cross-correlations between the reconstructed reference and the target plane images, 3D location data of the target object can be extracted from the correlation outputs. With the purpose of showing the feasibility of the proposed method, some computational and optical experiments on the target objects in space are carried out and the results are presented.     

利用螺旋型波带片进行边缘增强成像

为了提高对等离子体内界面区域的诊断精度,研究了利用螺旋型波带片实现边缘增强成像的技术。制作了用于可见光波段的一阶螺旋型波带片,最外环宽度3μm。利用螺旋型波带片对振幅式物体进行了边缘增强成像,实验获得了成像物体内边界区域的清晰图像,界面区域的成像强度得到很大增强。通过实验测量发现,当物距在菲涅耳衍射区域内时,螺旋型波带片也能够获取较好的成像质量,表明螺旋型波带片具有较大的视场角,能够对大尺度物体进行边缘成像。基于螺旋型波带片的边缘增强成像可以弥补传统成像方式对界面区域成像的不足,提高对等离子体内界面区域的诊断能力。     

Two-dimensional temporal coherence coding for super resolved imaging

In this paper, we present an approach that can be used for transmission of 2D spatial information through space-limited systems capable of transmitting even only a single spatial pixel. The input 2D object is illuminated with temporally incoherent illumination. The axial coherence length is very short and it equals only a few microns. Attached to the input object spatial random phase mask generates different axial shift for every pixel of the input. The temporal delays of the encoding (axial shifts) of every pixel are longer than the coherence length of the illuminating source. Therefore no temporal correlation exists between the various pixels of the input. A lens combines all spatial pixels into one point at its focal plane. Although the various spatial pixels were mixed together, since the random mask provided axial delay which was larger than the coherence length of the light source, the orthogonality between the spatial content of every pixel is preserved. The decoding system includes a lens that is positioned at the output of the resolution reduction system and it converts the output light into a plane wave containing all the spatial information of the original image mixed together in all of its pixels. By interfering this plane wave with the same plane wave after passing through the same random spatial coding mask, the spatial information of every pixel of the input object is recovered.     

一种自动提取目标的主动轮廓法

提出一种新的广泛应用于数字图象分析和计算机视觉的主动轮廓(Snake)模型,引入作用方向可以自适应变化的外加强制力,使控制点能够不依赖于初始轮廓而快速地收敛到目标的真实轮廓;初始轮廓自动确定;控制点的数目可以自适应地改变;能够在背景比较复杂的图象中实现对目标轮廓的提取.用该模型对空中目标的红外图象进行的实验结果表明其具有很好的鲁棒性和实用性.     

Correlation with spherical wave illumination

In the classical Van der Lugt correlator the plane wave illumination beam has been replaced by a spherical wave to avoid overshining of the undiffracted light in the photographic emulsion when weakly modulated objects have to be correlated. So the object information will be spread over a larger hologram area and an additional spatial frequency filter may be introduced without lengthening the experimental arrangement.     

基于差分图像的运动目标跟踪与分割方法的应用研究

提出了一种基于差分图像运动检测和轮廓提取的跟踪与分割图像的方法。该方法首先从初始图像中提取目标的轮廓,然后利用相邻帧之间的差分图像初步确定目标在每帧图像中的粗略位置,最后把从上一帧图像中得到的目标轮廓置于该位置,并作为轮廓提取的初始值,由此可得到对目标的准确分割。     

输出环状光束的新型激光谐振腔

提出一种输出环状光束的新型激光谐振腔,即在稳定激光谐振腔中采用外环耦合方式得到环状光束的输出。利用For-Li数值迭代算法求解此类激光谐振腔的积分方程,通过计算机编程计算了平面一凹球面稳定谐振腔的输出端平面镜在不同半径的情况下,谐振腔镜面上和衍射耦合输出场基模的振幅和相位分布。计算结果预示了当输出端平面镜半径小于通常的稳定腔的基模半径时,衍射耦合输出场有稳定的环状光束输出。实验中TEA CO2激光器采用印刷电路板预电离结构,增益长度90cm,腔长5m,球面全反射镜曲率半径20m,输出端平面镜半径4．5mm,得到了内环半径为4．5mm、外环半径为5．5mm的基模环形光斑输出。从而在理论上和实验上证实了该方案产生环状光束的可行性。     

Holding characteristics of planar objects suspended by near-field acoustic levitation

The authors have found the acoustic levitation phenomenon where planar objects of 10 kg weight can be levitated near a vibration surface. This phenomenon has been studied for non-contact transportation. A circular planar object can be suspended without contacting a circular vibration plate. We have studied the holding force which acts horizontally on the levitated objects. The horizontal position of the object is stabilized by this force. In this paper, we discuss the effect of the radius of a levitated object, levitation distance, displacement amplitude of the vibration plate and the vibration mode on the suspending force.     

Optical tweezers for confocal microscopy

In confocal laser scanning microscopes (CLSMs), lasers can be used for image formation as well as tools for the manipulation of microscopic objects. In the latter case, in addition to the imaging lasers, the light of an extra laser has to be focused into the object plane of the CLSM, for example as optical tweezers. Imaging as well as trapping by optical tweezers can be done using the same objective lens. In this case, z-sectioning for 3D imaging shifts the optical tweezers with the focal plane of the objective along the optical axis, so that a trapped object remains positioned in the focal plane. Consequently, 3D imaging of trapped objects is impossible without further measures. We present an experimental set-up keeping the axial trapping position of the optical tweezers at its intended position whilst the focal plane can be axially shifted over a distance of about 15 μm. It is based on fast-moving correctional optics synchronized with the objective movement. First examples of application are the 3D imaging of chloroplasts of Elodea densa (Canadian waterweed) in a vigorous cytoplasmic streaming and the displacement of zymogen granules in pancreatic cancer cells (AR42 J). Received: 24 March 2000 / Revised version: 23 June 2000 / Published online: 11 October 2000     

Measurement of tilt of a diffuse object by double-exposure speckle photography using speckle fanning in a photorefractive BaTiO3 crystal

A technique has been proposed for the measurement of tilt of a diffuse object using speckle fanning in a photorefractive BaTiO₃ crystal. Free space geometry has been used for recording in which the axis of rotation of the object lies away in three-dimensional space. The method is based on recording of two exposures, one before- and another after the tilt, thus producing speckle correlation fringes due to overlapping of two speckle fans. We consider a generalized case of tilt, generating curved fringes with center shifted in the transverse direction. The axis of rotation lies perpendicular to the optical axis in three-dimensional space having the transverse and axial components of the shift in the center of rotation with respect to the diffuser plane. Fourier transform of the curved fringes produces correlation output. Measure of separation between the correlation peaks in transverse and axial directions provides information about the tilt angle, the direction of tilt, and the distance of rotation axis from the optical axis. Experimental results have been presented to validate the theoretical predictions.     

Selective edge enhancement in three-dimensional vortex imaging with incoherent light

We demonstrate a new imaging method enabling a selective edge contrast enhancement of three-dimensional amplitude objects with spatially incoherent light. The imaging process is achieved in a spiral modification of Fresnel incoherent correlation holography and uses a vortex impulse response function. The correlation recordings of the object are acquired in a one-way interferometer with the wavefront division carried out by a spatial light modulator. Two different methods based on applying a helical reference wave in the hologram recording and a digital spiral phase modulation in image reconstruction are proposed for edge enhancement of amplitude objects. Results of both isotropic and anisotropic spiral imaging are demonstrated in experiments using an LED as an incoherent source of light.