摘要 :
The determination of numerical reconstruction distance is key to recover the wavefront at focal plane in digital holography. In this paper, we propose a new autofocus method based on angular spectrum method (ASM). The proposed met...
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The determination of numerical reconstruction distance is key to recover the wavefront at focal plane in digital holography. In this paper, we propose a new autofocus method based on angular spectrum method (ASM). The proposed method takes successive Fourier transform after 1st order spectrum selection, and then calculates the summation. It saves operations compared to classic autofocus functions. When an exhaustive z-axis search is performed, the proposed method obtains unimodality coincided with the results from four classic autofocus functions. Moreover, the proposed method is more time-effective, which is the optimal one for ASM.
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摘要 :
The determination of numerical reconstruction distance is key to recover the wavefront at focal plane in digital holography. In this paper, we propose a new autofocus method based on angular spectrum method (ASM). The proposed met...
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The determination of numerical reconstruction distance is key to recover the wavefront at focal plane in digital holography. In this paper, we propose a new autofocus method based on angular spectrum method (ASM). The proposed method takes successive Fourier transform after 1st order spectrum selection, and then calculates the summation. It saves operations compared to classic autofocus functions. When an exhaustive z-axis search is performed, the proposed method obtains unimodality coincided with the results from four classic autofocus functions. Moreover, the proposed method is more time-effective, which is the optimal one for ASM.
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摘要 :
In previous work, we have presented the maximum contrast autofocus algorithm for estimating unknown imaging parameters, e.g., for imaging through complicated surfaces using a flexible ultrasonic array. This paper details recent im...
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In previous work, we have presented the maximum contrast autofocus algorithm for estimating unknown imaging parameters, e.g., for imaging through complicated surfaces using a flexible ultrasonic array. This paper details recent improvements to the algorithm. The algorithm operates by maximizing the image contrast metric with respect to the imaging parameters. For a flexible array, the relative positions of the array elements are parameterized using a cubic spline function and the spline control points are estimated by iterative maximisation of the image contrast via simulated annealing. The resultant spline gives an estimate of the array geometry and the profile of the surface that it has conformed to, allowing the generation of a well-focused image. A pre-processing step is introduced to obtain an initial estimate of the array geometry, reducing the time taken for the algorithm to convergence. Experimental results are demonstrated using a flexible array prototype.
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This paper presents a relaxation-based autofocus (AUTORELAX) algorithm that can be used to compensate for the aperture errors in curvilinear synthetic aperture radar (CLSAR) and to extract threedimensional target features. The dat...
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This paper presents a relaxation-based autofocus (AUTORELAX) algorithm that can be used to compensate for the aperture errors in curvilinear synthetic aperture radar (CLSAR) and to extract threedimensional target features. The data model for the autofocus problem in CLSAR is presented. Experimental and simulation results show that AUTORELAX can be used to significantly improve the estimation accuracy of the target parameters.
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Autofocus is a methodology for estimating and correcting errors in the assumed parameters of an imaging algorithm. It provides improved image quality and, therefore, better defect detection and characterization capabilities. In th...
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Autofocus is a methodology for estimating and correcting errors in the assumed parameters of an imaging algorithm. It provides improved image quality and, therefore, better defect detection and characterization capabilities. In this paper, we present a new autofocus algorithm developed specifically for ultrasonic non-destructive testing and evaluation (NDE). We consider the estimation and correction of errors in the assumed element positions for a flexible ultrasonic array coupled to a specimen with an unknown surface profile. The algorithm performs a weighted least-squares minimization of the time-of-arrival errors in the echo data using assumed models for known features in the specimen. The algorithm is described for point and planar specimen features and demonstrated using experimental data from a flexible array prototype.
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To provide smooth viewing experience, the design of continuous autofocus of video cameras needs to take the scene dynamics into consideration in the algorithm development and testing cycles. However, this is often a time-consuming...
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To provide smooth viewing experience, the design of continuous autofocus of video cameras needs to take the scene dynamics into consideration in the algorithm development and testing cycles. However, this is often a time-consuming and tedious process because it requires a huge amount of tests on various real scenes. We propose in this paper a simulation method to simplify the digital autofocus design process. This design-by-simulation method significantly reduces the development and testing time of the search strategy for digital autofocus. Experimental results are shown to demonstrate the effectiveness of the proposed method.
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摘要 :
To provide smooth viewing experience, the design of continuous autofocus of video cameras needs to take the scene dynamics into consideration in the algorithm development and testing cycles. However, this is often a time-consuming...
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To provide smooth viewing experience, the design of continuous autofocus of video cameras needs to take the scene dynamics into consideration in the algorithm development and testing cycles. However, this is often a time-consuming and tedious process because it requires a huge amount of tests on various real scenes. We propose in this paper a simulation method to simplify the digital autofocus design process. This design-by-simulation method significantly reduces the development and testing time of the search strategy for digital autofocus. Experimental results are shown to demonstrate the effectiveness of the proposed method.
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摘要 :
Based on the theory of phase gradient autofocus on airborne SAR, an improved algorithm for reducing the phase gradient autofocus computation is provided in this paper. According to the image contrast criterion, some isolated stron...
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Based on the theory of phase gradient autofocus on airborne SAR, an improved algorithm for reducing the phase gradient autofocus computation is provided in this paper. According to the image contrast criterion, some isolated stronger scatters for estimation phase errors are chosen, and then a new way to select windows width is developed, which can accelerate the convergence of the autofocus. Point target simulation is carried out, which verify the feasibility and the validity of this algorithm. The present algorithm can estimate discretional rank phase errors and doesnpsilat require strong reflection point, which is up to accuracy. After decreasing the computation of this algorithm, it is more suitable for real-time processing.
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摘要 :
Based on the theory of phase gradient autofocus on airborne SAR, an improved algorithm for reducing the phase gradient autofocus computation is provided in this paper. According to the image contrast criterion, some isolated stron...
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Based on the theory of phase gradient autofocus on airborne SAR, an improved algorithm for reducing the phase gradient autofocus computation is provided in this paper. According to the image contrast criterion, some isolated stronger scatters for estimation phase errors are chosen, and then a new way to select windows width is developed, which can accelerate the convergence of the autofocus. Point target simulation is carried out, which verify the feasibility and the validity of this algorithm. The present algorithm can estimate discretional rank phase errors and doesnpsilat require strong reflection point, which is up to accuracy. After decreasing the computation of this algorithm, it is more suitable for real-time processing.
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摘要 :
A thermography autofocus system based on stepping motor control is designed for air leak location. DFF (Depth From Focus) is adopted to realize the autofocus of thermography. Firstly, a focusing target is designed, and then the ho...
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A thermography autofocus system based on stepping motor control is designed for air leak location. DFF (Depth From Focus) is adopted to realize the autofocus of thermography. Firstly, a focusing target is designed, and then the horizontal temperature distribution of its thermal image is operated by using energy gradient function as the evaluation function of edge detection, finally the hill climbing method is used to achieve the optimal focusing position. The theoretical analysis and experimental results show that the adopted control scheme and evaluation function can obtain a very good focusing effect and effectively overcome the virtuality of images caused by the position difference of the tested object.
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