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ACQUISITION OF THE CURVES OF THE HUMAN CRYSTALLINE LENS FROM SLIT LAMP imageS - AN APPLICATION OF THE HOUGH TRANSFORM

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APPLIED OPTICS 1991年第16期30卷 2088-2099页

作者： COOK, CA KORETZ, JF []The authors are with Rensselaer Polytechnic Institute Center for Biophysics Troy New York 12180-3590.

To accurately model lens-based functions such as accommodation and image formation on the retina, it is essential to know anterior chamber depth, anterior segment length, lens thickness, and, most importantly, lens curvature both on the surfaces and internally. With the exception of lens curvatures, all these data can be obtained with a high of precision by one or more techniques (i.e., A-scan ultrasonography and pachymetry). Lens curvatures can be collected by Scheimpflug slit lamp photography, but the curvature data must be extracted from these images, a problem complicated by both linear and nonlinear image distortion. Previous approaches have involved significant magnification of the image combined with major subjective input and judgment. We present here a computer-based application of the Hough technique for measurement of curvature of lens surfaces observed in Scheimpflug slit lamp photography and related evaluation of (and solutions for) the associated image distortion. Minimal user input is required for successful application of this method, but the time required to obtain a fit for each surface is > 1 min. Results obtained by this technique on test images compare favorably with those obtained by independent methods.

关键词： Crystalline lens Digital image processing image metrics image processing algorithms Refractive anomalies Retina scanning

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VIEW ANGLE TRANSFORMATIONS

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PATTERN RECOGNITION LETTERS 1991年第5期12卷 273-278页

作者： KOMEN, ER Pattern Recognition Group Faculty of Applied Physics Delft University of Technology Lorentzweg 1 2628 CL Delft Netherlands

A novel object operation is proposed, where each point in a destination image contains the value of the 'view angle' with which it can see the object in the source image. Thesholding a view angle image at 180-... 详细信息

关键词： VIEW ANGLE TRANSFORMATION image processing algorithms

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Compensation method for projector calibration based on homography and bundle adjustments

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OSA CONTINUUM 2020年第11期3卷 3157-3175页

作者： Lin, Junyi Zhang, Xuefeng Wang, Yushu Wu, Lei Jiang, Kaiyong Huaqiao Univ Fujian Prov Key Lab Special Energy Mfg Xiamen Key Lab Digital Vis Measurement Xiamen 361021 Fujian Peoples R China

Projector calibration is one of the most essential steps for structured light systems. Some methods have high precision but require a complicated calibration procedure, such as the method based on phase-shifting. Other methods take advantage of simple implementation but cannot meet the accuracy requirement, for example, the method based on homography. In this paper, we proposed a compensation method for flexible and accurate projector calibration. To make the calibration procedure easy to operate, the homographic matrix between the projector and camera is established through feature points projected. Then, the 2D image points compensation method based on the re-projection error iteration algorithm was carried out, and a modified bundle adjustment (BA) algorithm is put forward to refine the calibration parameters of the system. Finally, the feature point reconstruction experiment is implemented to verify the high flexibility and accuracy performance of the proposed method. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： Calibration Digital image correlation image processing algorithms Stereo matching Structured light Virtual reality

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Detail enhancement for infrared images based on Relativity of Gaussian-Adaptive Bilateral Filter

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OSA CONTINUUM 2021年第10期4卷 2671-2686页

作者： Feng, Xiongwei Pan, Zhongliang South China Normal Univ Sch Phys & Telecommun Engn Guangzhou 510006 Peoples R China

Detail enhancement is the key to the display of infrared image. For the infrared image detail enhancement algorithms, it is very important to present a good visual effect for people effectively. A novel algorithm for detail enhancement of infrared images is proposed in this paper. The method is based on the relativity of Gaussian-adaptive bilateral Filter. The algorithm consists of three steps. The first step is to divide the input image into the base layer and the detail layer by the relativity of Gaussian-adaptive bilateral filter. In the second step, the detail layer is multiplied by the proposed weight coefficient, and the base layer is processed by histogram projection. The third step is to combine the detail layer and the base layer processed in the second step and output it to the 8-bit domain display. Compare with other methods, the new algorithm reduces the running time greatly. The experimental results showed that the proposed algorithm improves the contrast of infrared images effectively. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： image enhancement image fusion image processing algorithms image quality Imaging systems Thermal imaging

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Sub-pixel dimensional measurement algorithm based on intensity integration threshold

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OSA CONTINUUM 2020年第10期3卷 2912-2924页

作者： Chu, Menglin Huang, Wei Xu, Mingfei Jia, Shuqiang Zhang, Xiaofei Lu, Yongnan Chinese Acad Sci Changchun Inst Opt Fine Mech & Phys 3888 Dong Nanhu Rd Changchun 130033 Peoples R China Univ Chinese Acad Sci 19 A Yuquan Rd Beijing 100049 Peoples R China Changchun Univ Sci & Technol 7089 Weixing Rd Changchun 130022 Peoples R China Chinese Acad Sci Dalian Inst Chem Phys 457 Zhongshan Rd Dalian 116023 Peoples R China

In this paper, we proposed a sub-pixel measurement algorithm based on intensity integration threshold (IIT). The proposed method can localize the sub-pixel edges in an inexpensive way by calculating the integration of the intensity across the edge and finding the point where the integration reaches the threshold. Comparative tests show our method realized better efficiency and robustness in practical applications than other state-of-the-art algorithms. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

关键词： algorithms Edge detection image processing image processing algorithms Machine vision Wavelet transforms

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A LISP-BASED image-ANALYSIS SYSTEM WITH APPLICATIONS TO MICROSCOPY

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JOURNAL OF MICROSCOPY-OXFORD 1987年第1期148卷 51-87页

作者： BRIGHT, DS Chemistry A121 National Bureau of Standards Gaithersburg MD 20899 U.S.A.

SUMMARYLISPIX is an image processing and analysis system consisting of a sub‐system of image processing commands implemented in FORTRAN and a collection of analysis algorithms implemented in LISP. Examples are given of using the system for microanalysis applications. The processing commands are useful alone for simple tasks. For analysis applications, the LISP programming environment, for which the processing commands are designed, allows rapid development of algorithms and a convenient way to use them. Appendices contain definitions of the most useful commands as well as examples of the LISP algorithm

关键词： image analysis image analysis system image processing image processing algorithms LISP microanalysis

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Endoscopic image enhancement with noise suppression

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HEALTHCARE TECHNOLOGY LETTERS 2018年第5期5卷 154-157页

作者： Xia, Wenyao Chen, Elvis C. S. Peters, Terry Univ Western Ontario Med Biophys 1151 Richmond St London ON Canada Robarts Res Inst 1151 Richmond St North London ON Canada

Stereoscopic endoscopes have been used increasingly in minimally invasive surgery to visualise the organ surface and manipulate various surgical tools. However, insufficient and irregular light sources become major challenges for endoscopic surgery. Not only do these conditions hinder image processing algorithms, sometimes surgical tools are barely visible when operating within low-light regions. In addition, low-light regions have low signal-to-noise ratio and metrication artefacts due to quantisation errors. As a result, present image enhancement methods usually suffer from heavy noise amplification in low-light regions. In this Letter, the authors propose an effective method for endoscopic image enhancement by identifying different illumination regions and designing the enhancement design criteria for desired image quality. Compared with existing image enhancement methods, the proposed method is able to enhance the low-light region while preventing noise amplification during image enhancement process. The proposed method is tested with 200 images acquired by endoscopic surgeries. Computed results show that the proposed algorithm can outperform state-of-the-art algorithms for image enhancement, in terms of naturalness image quality evaluator and illumination index.

关键词： biomedical optical imaging desired image quality different illumination regions endoscopes endoscopic image enhancement endoscopic surgery enhancement design criteria existing image enhancement methods heavy noise amplification illumination index image enhancement image enhancement process image processing image processing algorithms insufficient light sources irregular light sources low signal-to-noise ratio low-light region medical image processing medical robotics minimally invasive surgery naturalness image quality evaluator noise suppression stereoscopic endoscopes surgery surgical tools

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PHASE-GRADIENT ALGORITHM AS AN OPTIMAL ESTIMATOR OF THE PHASE DERIVATIVE

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OPTICS LETTERS 1989年第20期14卷 1101-1103页

作者： EICHEL, PH JAKOWATZ, CV []Sandia National Laboratories Albuquerque New Mexico 87185

The phase-gradient algorithm represents a powerful new signal-processing technique with applications to aperture-synthesis imaging. These include, for example, synthetic-aperture-radar phase correction and stellar-image reconstruction. The algorithm combines redundant information present in the data to arrive at an estimate of the phase derivative. We show that the estimator is in fact a linear, minimum-variance estimator of the phase derivative.

关键词： algorithms image processing algorithms Point spread function Power spectra Speckle imaging Speckle noise

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CROSS-SPECTRUM ERROR CRITERION AS AN image QUALITY MEASURE

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APPLIED OPTICS 1974年第6期13卷 1460-1465页

作者： TESCHER, AG PARSONS, JR AEROSP CORP POB 95085LOS ANGELESCA 90045

Various criteria have been considered for image quality measure. Some of these involve subjective human visual evaluation, while others rely on statistical techniques. In this paper, a cross-spectrum error criterion is considered as a distortion measure for undersampled band-limited images. The effect of undersampling, aliasing on the perfect image, is demonstrated by manipulation in the frequency domain. Subjective comparison of the digital simulation results and the appropriate calculated spectral error indicate that the latter is a useful quantity for the analysis of distortion present in undersampled images. Relevance of our analysis to spatial filtering experiments and the mean square error is also discussed.

关键词： Digital image processing Fast Fourier transforms image metrics image processing algorithms image quality Spatial filtering

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Measuring the refractive index of scintillation crystal with a Mach-Zehnder interferometer

OPTICS CONTINUUM

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OPTICS CONTINUUM 2022年第4期1卷 909-918页

作者： Liu, Xinyue Long, Jiale Ding, Yi Hu, Yi Du, Zihao Xu, Bin Deng, Dingnan Wuyi Univ Dept Intelligent Mfg Jiangmen 529020 Guangdong Peoples R China Jiaying Univ Sch Phys & Elect Engn Meizhou 514015 Guangdong Peoples R China

The refractive index of the scintillation crystal is a key parameter in the design of Positron Emission Tomography (PET) devices. However, existing methods to measure the refractive index always suffer from problems such as the complexity of optical path adjustment, long time cost, or high equipment consumption. To overcome these problems, we propose a method that can obtain the refractive index of the scintillation crystal with high accuracy in real time. In this method, we employ the Mach-Zehnder interferometer to generate the interference pattern when one beam of light passes through the scintillation crystal, which encodes the value of refractive index into the width of pattern. To obtain the width of interference pattern, we calculate the width pixels of dark/bright stripes in pattern with threshold, respectively, and finally get the average number of pixels of the pattern;this strategy can eliminate the coherent interference signal and random noise effectively. The optical path need not adjust during the whole measurement. Thus, the refractive index of scintillation crystals can be measured with reliability and efficiency. To validate the effectiveness of the proposed method, we measure different batches of BGO crystal and Ce:LYSO crystal samples. The results show that the proposed method can measure refractive indices with high accuracy and high efficiency, providing a reliable crystal refractive index measurement procedure for the PET detector module design. The proposed method is also suitable for refractive index measurements of transparent materials in visible light bands.

关键词： Digital image processing image processing algorithms Index measurements Mach Zehnder interferometers Refractive index Visible light

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