Adjustable active optical low-pass filter

This paper presents an active optical low-pass filter (AOLPF) capable of changing the resolution of an imaging system on demand in order to remove aliasing noise from a sampling image. This is advantageous over conventional optical low-pass filters, which are fixed image-blurring optical components that are built into the imaging system, in order to remove aliasing in the image. Furthermore, conventional filters smear images regardless of the presence or lack of high spatial frequency, which can exceed the Nyquist limit of the sensor. On the contrary, the proposed AOLPF can dynamically adjust the modulation transfer function of an imaging system to eliminate aliasing artifacts. In addition, this filter can be turned off in the absence of high spatial frequency to maximize resolution and prevent unnecessary blurring of the sampling image.     

基于变分贝叶斯多图像超分辨的平面复眼空间分辨率增强

平面复眼成像系统利用多个子孔径对场景进行成像,由于子孔径大小和图像传感器空间采样率的限制,各子孔径图像质量较差。如何融合多个子孔径图像来获得高分辨率图像是亟需解决的问题。多图像超分辨理论利用多幅具有互补信息的图像来重构高空间分辨率图像,然而现有理论通常采用过于简化的运动模型,这种简化的运动模型对平面复眼成像并不完全适用。若直接把现有多图像超分辨理论用于平面复眼分辨率增强,不准确的相对运动估计将降低图像分辨率增强性能。针对这些问题,本文在变分贝叶斯框架下改进了现有多图像超分辨理论中的运动模型,并把导出的联合估计算法用于平面复眼分辨率增强。仿真数据实验和真实复眼数据实验验证了推荐方法的正确性和有效性。     

Upscaling image resolution of compact imaging systems using wavefront coding and a property of the point-spread function

We propose an image-resolution upscaling method for compact imaging systems. The image resolution is calculated using the resolving power of the optics and the pixel size of a digital image sensor. The resolution limit of the compact imaging system comes from its size and the number of allowed lenses. To upscale the image resolution but maintain the small size, we apply wavefront coding and image restoration. Conventional image restoration could not enhance the image resolution of the sensor. Here, we use the upscaled image of a wavefront-coded optical system and apply an image-restoration algorithm using a more precisely calculated point-spread function (PSF) as the deconvolution filter. An example of a wavefront-coded optical system with a 5-megapixel image sensor is given. The final image had a resolution equivalent to that of a 10-megapixel image using only four plastic lenses. Moreover, image degradation caused by hand motion could also be reduced using the proposed method.     

动态波前相位的高分辨率测量

动态波前相位信息测量是大气光学，气动光学和激光技术等领域的重要实验手段。提出了一种具有高的时间和空间分辨率以及长的测量持续时间的动态波前相位测量方法。应用Ｈａｒｔｍａｎｎ－Ｓｈａｃｋ波前传感器获得高空间分辨率的相位信息，采用高帧频ＣＣＤ摄象机获得高时间分辨率图象数据。     

Random-phase-shift Fizeau interferometer

A new and potentially cost efficient kind of vibration-tolerant surface measurement interferometer based on the Fizeau-principle is demonstrated. The crucial novelty of this approach is the combination of two optoelectronic sensors: an image sensor with high spatial resolution and an arrangement of photodiodes with high temporal resolution. The photodiodes continuously measure the random-phase-shifts caused by environmental vibrations in three noncollinear points of the test surface. The high spatial resolution sensor takes several "frozen" images of the test surface by using short exposure times. Under the assumption of rigid body movement the continuously measured phase shifts of the three surface points enable the calculation of a virtual plane that is representative for the position and orientation of the whole test surface. For this purpose a new random-phase-shift algorithm had to be developed. The whole system was tested on an optical table without vibration isolation under the influence of random vibrations. The analysis of the root-mean-square (RMS) over ten different measurements shows a measurement repeatability of about 0.004 wave (approximately 2.5 nm for 632.8 nm laser wavelength).     

Coding for compressive focal tomography

We consider the capabilities and limits of strategies for single-aperture three-dimensional and extended depth of field optical imaging. We show that reduced spatial resolution is implicit in forward models for light field sampling and that reduced modulation transfer efficiency is intrinsic to pupil coding. We propose a novel strategy based on image space modulation and show that this strategy can be sensitive to high-resolution spatial features across an extended focal volume.     

Attenuated total reflection-Fourier transform infrared imaging of large areas using inverted prism crystals and combining imaging and mapping

Attenuated total reflection-Fourier transform infrared (ATR-FT-IR) imaging is a very useful tool for capturing chemical images of various materials due to the simple sample preparation and the ability to measure wet samples or samples in an aqueous environment. However, the size of the array detector used for image acquisition is often limited and there is usually a trade off between spatial resolution and the field of view (FOV). The combination of mapping and imaging can be used to acquire images with a larger FOV without sacrificing spatial resolution. Previous attempts have demonstrated this using an infrared microscope and a Germanium hemispherical ATR crystal to achieve images of up to 2.5 mm x 2.5 mm but with varying spatial resolution and depth of penetration across the imaged area. In this paper, we demonstrate a combination of mapping and imaging with a different approach using an external optics housing for large ATR accessories and inverted ATR prisms to achieve ATR-FT-IR images with a large FOV and reasonable spatial resolution. The results have shown that a FOV of 10 mm x 14 mm can be obtained with a spatial resolution of approximately 40-60 microm when using an accessory that gives no magnification. A FOV of 1.3 mm x 1.3 mm can be obtained with spatial resolution of approximately 15-20 microm when using a diamond ATR imaging accessory with 4x magnification. No significant change in image quality such as spatial resolution or depth of penetration has been observed across the whole FOV with this method and the measurement time was approximately 15 minutes for an image consisting of 16 image tiles.     

Determination of the optimum sampling frequency of noisy images by spatial statistics

In optical metrology the final experimental result is normally an image acquired with a CCD camera. Owing to the sampling at the image, an interpolation is usually required. For determining the error in the measured parameters with that image, knowledge of the uncertainty at the interpolation is essential. We analyze how kriging, an estimator used in spatial statistics, can generate convolution kernels for filtering noise in regularly sampled images. The convolution kernel obtained with kriging explicitly depends on the spatial correlation and also on metrological conditions, such as the random fluctuations of the measured quantity, and the resolution of the measuring devices. Kriging, in addition, allows us to determine the uncertainty of the interpolation, and we have analyzed it in terms of the sampling frequency and the random fluctuations of the image, comparing it with Nyquist criterion. By use of kriging, it is possible to determine the optimum-required sampling frequency for a noisy image so that the uncertainty at interpolation is below a threshold value.     

高分辨率便携式管道锈蚀检测仪

设计了一套高分辨率的便携式 X 射线管道锈蚀检测仪, 该检测仪成像空间分辨率为 3 lp/mm, 透度灵敏度为 1.6%. 在检测仪的设计过程中, 利用 CsI 转换屏将射线转换为可见光、利用微光慢扫描 CCD 相机成像, 在笔记本电脑的远程控制下, 由图像采集器获取射线数字图像并通过网络传输至笔记本电脑进行处理、显示和存盘等工作, 利用基于统计特性的自适应边缘增强次序滤波对管道锈蚀图像进行降噪增强处理, 取得了较好的效果. 实验结果表明, 该检测仪可清楚地显示管道内部结垢、堵塞、腐蚀等情况.     

ACTIVE-EYES: an adaptive pixel-by-pixel image-segmentation sensor architecture for high-dynamic-range hyperspectral imaging

The ACTIVE-EYES (adaptive control for thermal imagers via electro-optic elements to yield an enhanced sensor) architecture, an adaptive image-segmentation and processing architecture, based on digital micromirror (DMD) array technology, is described. The concept provides efficient front-end processing of multispectral image data by adaptively segmenting and routing portions of the scene data concurrently to an imager and a spectrometer. The goal is to provide a large reduction in the amount of data required to be sensed in a multispectral imager by means of preprocessing the data to extract the most useful spatial and spectral information during detection. The DMD array provides the flexibility to perform a wide range of spatial and spectral analyses on the scene data. The spatial and spectral processing for different portions of the input scene can be tailored in real time to achieve a variety of preprocessing functions. Since the detected intensity of individual pixels may be controlled, the spatial image can be analyzed with gain varied on a pixel-by-pixel basis to enhance dynamic range. Coarse or fine spectral resolution can be achieved in the spectrometer by use of dynamically controllable or addressable dispersion elements. An experimental prototype, which demonstrated the segmentation between an imager and a grating spectrometer, was demonstrated and shown to achieve programmable pixelated intensity control. An information theoretic analysis of the dynamic-range control aspect was conducted to predict the performance enhancements that might be achieved with this architecture. The results indicate that, with a properly configured algorithm, the concept achieves the greatest relative information recovery from a detected image when the scene is made up of a relatively large area of moderate-dynamic-range pixels and a relatively smaller area of strong pixels that would tend to saturate a conventional sensor.     

Tactile Sensing Using Force Sensing Resistors and a Super-Resolution Algorithm

This paper presents a tactile sensor consisting of an array of force sensing resistors (FSRs). The tactile sensing array can be seen as a coordinated system of touch sensors. The low spatial resolution measured with the FSRs compared to other force or pressure sensors required the use of a super-resolution algorithm. Super-resolution algorithms are often used in digital image processing to enhance the resolution of images. Multiple images taken from slightly different orientations are superimposed in such a way that a single higher-resolution image is obtained. Different touch sensors are briefly discussed and the use of FSRs is motivated. Image-registration techniques are discussed and the super-resolution algorithm developed for the application is presented. Some tests performed using the tactile sensor in a neck palpation device and the results of these tests are also presented.      

Planar reflection grating lens for compact spectroscopic imaging system

A compact spectroscopic imaging device consisting of a planar reflection grating lens, a probe fiber array, and a two-dimensional image sensor was proposed and discussed. Reflected or luminescent lights from a subject are coupled to the probe fibers, guided to fiber output ends, radiated into the air, diffracted by the grating lens with wavelength-dependent angle, and focused onto lines on the image sensor. Two-dimensional intensity distribution on the image sensor can give one-dimensional spectrum distribution along a specified direction. A grating lens was designed with a fiber array and a CCD image sensor for 100-nm wavelength range and 10-mm fiber array width. A spectral resolution of 5 nm and a spatial resolution of 0.25 mm were experimentally confirmed.     

Wavefront sensor based on the Talbot effect with the precorrected holographic grating

A holographic wavefront sensor based on the Talbot effect is proposed. Optical wavefronts are measured by sampling the light amplitude distribution with a two-dimensional (2D) precorrected holographic grating. The factors that allow changing an angular measurement range and a spatial resolution of the sensor are discussed. A comparative analysis with the Shack-Hartmann sensor is illustrated with some experimental results.     

50th Anniversary Article: Effect of Sensor Noise on the Resolution and Spatial Resolution of Displacement and Strain Maps Estimated with the Grid Method

This paper deals with noise propagation from camera sensor to displacement and strain maps when the grid method is employed to estimate these quantities. It is shown that closed‐form equations can be employed to predict the link between metrological characteristics such as resolution and spatial resolution in displacement and strain maps on the one hand and various quantities characterising grid images such as brightness, contrast and standard deviation of noise on the other hand. Various numerical simulations confirm first the relevance of this approach in the case of an idealised camera sensor impaired by a homoscedastic Gaussian white noise. Actual CCD or CMOS sensors exhibit, however, a heteroscedastic noise. A pre‐processing step is therefore proposed to first stabilise noise variance prior to employing the predictive equations, which provide the resolution in strain and displacement maps due to sensor noise. This step is based on both a modelling of sensor noise and the use of the generalised Anscombe transform to stabilise noise variance. Applying this procedure in the case of a translation test confirms that it is possible to model correctly noise propagation from sensor to displacement and strain maps, and thus also to predict the actual link between resolution, spatial resolution and standard deviation of noise in grid images.     

SRR在多线阵错位排列扫描系统中的实现

为了获得尽可能高的空间分辨率的图像,超分辨率重构技术(SRR)成为了红外扫描成像的研究热点.本文以红外多线阵错位排列扫描成像系统为研究平台,通过分析SRR实现过程及待重构图像获取的方式,分析了红外多线阵错位排列扫描成像系统中SRR有效的关键.实验表明:对于固定错位量的多排传感器扫描成像系统,影响重构图像质量的主要因素是各通道所获得的待重构图像同位像素灰度不一致引入的噪声.本文提出的基于序列逐像素比较滤波法,可以大大提高重构图像质量.     

Mass spectrometry "sensor" for in vivo acetylcholine monitoring

Developing sensors for in vivo chemical monitoring is a daunting challenge. An alternative approach is to couple sampling methods with online analytical techniques; however, such approaches are generally hampered by lower temporal resolution and slow analysis. In this work, microdialysis sampling was coupled with segmented flow electrospray ionization mass spectrometry (ESI-MS) to perform in vivo chemical monitoring. The use of segmented flow to prevent Taylor dispersion of collected zones and rapid analysis with direct ESI-MS allowed 5 s temporal resolution to be achieved. The MS "sensor" was applied to monitor acetylcholine in the brain of live rats. The detection limit of 5 nM was sufficient to monitor basal acetylcholine as well as dynamic changes elicited by microinjection of neostigmine, an inhibitor of acetycholinesterase, that evoked rapid increases in acetycholine and tetrodotoxin, a blocker of Na(+) channels, that lowered the acetylcholine concentration. The versatility of the sensor was demonstrated by simultaneously monitoring metabolites and infused drugs.     

Digital-holographic interferometry with an image-intensifier system

A method for recording digital holograms on an image intensifier coupled with a CCD sensor is presented. The advantage of the image intensifier is that it can be gated (electronic shutter action produced by controlling of the image intensifier's photocathode voltage). This allows us to record holograms with a short exposure time. Two holograms of an object submitted to dynamical displacements (e.g., vibrations) are recorded by two short exposures. The phase of the wave front recorded at different times is calculated from the recorded intensity by use of a digital Fourier-transform method. By comparison of the phases recorded it is possible to get the displacement of the object during a short interval. Experimental results are presented, and the problems related to the noise and to the spatial resolution are discussed.     

Ultrasound synthetic aperture imaging: monostatic approach

An ultrasound synthetic aperture imaging method based on a monostatic approach was studied experimentally. The proposed synthetic aperture method offers good dynamical resolution along with fast numerical reconstruction. In this study complex object data were recorded coherently in a two-dimensional hologram using a 3.5 MHz single transducer with a fairly wide-angle beam. Image reconstruction which applies the wavefront backward propagation method and the near-field curvature compensation was performed numerically in a microcomputer using the spatial frequency domain. This approach allows an efficient use of the FFT-algorithms. Because of the simple and fast scanning scheme and the efficient reconstruction algorithms the method can be made real-time. The image quality of the proposed method was studied by evaluating the spatial and dynamical resolution in a waterbath and in a typical tissue-mimicking phantom. The lateral as well as the range resolution (-6 dB) were approximately 1 mm in the depth range of 30-100 mm. The dynamical resolution could be improved considerably when the beam width was made narrower. Although it resulted in a slightly reduced spatial resolution this compromise has to be done for better resolution of low-contrast targets such as cysts. The study showed that cysts as small as 2 mm by diameter could be resolved     

Texture augmented analysis of high resolution satellite imagery in detecting invasive plant species

Abstract

During recent decades, a considerable number of alien species have been brought into Taiwan and have caused significant impacts to local ecosystems and biodiversity. High resolution satellite imagery can provide detailed spatial characteristics over a large area and has a great potential for accurate vegetation mapping. However, most traditional multispectral image classification techniques focus on spectral discrimination of ground objects and may overlook useful spatial information provided by high resolution images. To achieve the best result, analysis of high resolution imagery should also incorporate spatial variations of the data. Therefore, this paper has looked into using a texture augmented procedure to analyze a high resolution satellite (QuickBird) image in order to detect an invasive plant species (Leucaena leucocephala) in southern Taiwan. Samples of primary vegetation covers were selected from the image to determine suitable texture analysis parameters for extracting texture features helpful for classification. Validation with ground truth data showed that the analysis produced high accuracies in detecting the target plant species and overall classification for primary vegetation types within the study site.     

一种改进的遥感图像融合方法

针对传统的IHS变换和Mallat算法在融合多光谱图像和高空间分辨力图像时存在的不足,提出了一种将IHS变换和平稳小波变换相结合的遥感图像融合方法;另外,对多光谱图像和高空间分辨力图像因空间分辨力的不同而带来的融合图像中所存在的虚假轮廓问题,提出在融合过程中先定位虚假轮廓出现的位置,然后加以处理的方法.仿真结果表明,本文算法在光谱失真上小于IHS变换法,克服了Mallat算法存在的方块效应,同时较好的抑制了虚假轮廓.