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检索条件"主题词=Wavefront coding"

共 157 条记录，以下是51-60 订阅

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Design of two-focus infrared system with lens-combined modulated wavefront coding technology 22

Design of two-focus infrared system with lens-combined modul...

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22nd Annual Conference on Novel Optical Systems, Methods, and Applications XXII

作者： Dong, Yueqi Zhao, Yuejin Dong, Liquan Liu, Ming Hui, Mei Du, Haoyuan Beijing Inst Technol Sch Opt & Photon Beijing Key Lab Precis Photoelect Measuring Instr Beijing 100081 Peoples R China

ISBN: (数字)9781510629042

ISBN: (纸本)9781510629042

In this report an infrared zoom optical system is discussed. This system shifts a single moving element to switch between two focal lengths(30mm/60mm), one for wide angle and the other for close-up. However, a conventional optics-only method cannot provide good imaging quality over a large depth of focus at each focus offset. To improve the imaging performance, we investigate a lens-combined modulated wavefront coding technology for extending the depth of focus. Instead of placing a phase mask at the pupil position like traditional wavefront coding does, all the element surfaces in the system contribute to achieving modulation transfer function (MTF) consistency over a large range of depth of focus under dual field-of-view settings. As a result, the new structure extends the depth of focus 6.5 times than that of the original system. We also demonstrate recovered images employing hyper-Laplacian priors with noise and artifacts suppressed. It is concluded that the novel structure can not only extend the depth of focus but also reduce the complexity of infrared optical system.

关键词： zoom lens depth of focus infrared optical system wavefront coding

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Research on signal-to-noise ratio characteristics and image restoration for wavefront coding 9

Research on signal-to-noise ratio characteristics and image ...

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9th Conference of Optics and Photonics for Information Processing

作者： Wu, Yijian Zhao, Yuejin Guo, Xiaohu Dong, Liquan Jia, Wei Liu, Ming Zhao, Ji Liu, Yun Beijing Inst Technol Sch Optoelect Beijing Key Lab Precis Optoelect Measurement Inst Beijing 100081 Peoples R China Typonteq Co Ltd Beijing 100081 Peoples R China

ISBN: (纸本)9781628417647

wavefront coding, a technique of optical-digital hybrid image, can be used to extend the depth of the field. However, it sacrifices the signal-to-noise ratio (SNR) of system at a certain degree, especially on focus situation. The on-focus modulation transfer function (MTF) of wavefront coding system is much lower than that of generally traditional optical system. And the noise will be amplified in the digital image processing. This paper analyzes characteristics of the SNR of the wavefront coding system in the frequency domain and calculates the rate of noise amplification in the digital processing. It also explains the influence of the image detector noise severely reducing the restored quality of images. In order to reduce noise amplification in the process of image restoration, we propose a modified wiener filter which is more suitable for restoration in consideration of noise suppression. The simulation experiment demonstrates that the modified wiener filter, compared with traditional wiener filter, has much better performance for wavefront coding system and the restored images having much higher SNR in the whole depth of the field.

关键词： wavefront coding spectral signal-to-noise ratio incremental wiener filter MTF image restoration

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Passive range measurement through wavefront coding

Passive range measurement through wavefront coding

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Conference on Two- and Three-Dimensional Methods for Inspection and Metrology IV

作者： Lis, Steven A. LightlLine Technol Inc Needham MA 02492 USA

ISBN: (纸本)9780819464804

Through the introduction of a simply designed phase mask at the pupil of a conventional imaging system, the range to objects in view can be precisely determined. The mask allows for roughly 50% light transmission, and is segmented to introduce a 1/4 wave phase shift into half of the transmitted light. The resulting point spread function is highly sensitive to object range and is incorporated into the resultant image. Through comparison of the wavefront coded image with a conventional image of the same scene, the precise range to the object can be determined. The range measurement precision obtained is directly related to image contrast. For objects having a simple linear edge possessing a contrast of 32 gray levels above noise, range can be measured to 1% precision. While based on an interference effect, wide-band polychromatic light can be used to determine object range. No actively moving components in the optical system are required for operation. The resultant approach allows for imaging and range determination simultaneously. Based on a fundamental interference phenomenon, this approach is applicable to all passive optical imaging systems ranging from the UV to the infrared. Both a theoretical analysis and an experimental verification of the approach showing the expected performance is provided.

关键词： range measurement wavefront coding deconvolution

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Optimizing trefoil phase plates design for color wavefront coding 19

Optimizing trefoil phase plates design for color wavefront c...

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19th Conference on Current Developments in Lens Design and Optical Engineering

作者： Olvera-Angeles, Miguel Padilla-Vivanco, Alfonso Ortega, Karina Sasian, Jose Schwiegerling, Jim Arines, Justo Acosta, Eva Univ Politecn Tulancingo Hidalgo 43629 Mexico Univ Arizona Coll Opt Sci Tucson AZ 85721 USA Univ Santiago de Compostela Fac Fis Santiago De Compostela 15782 Spain

ISBN: (数字)9781510620629

ISBN: (纸本)9781510620629

wavefront coding refers to the use of a phase modulating element in conjunction with deconvolution to extend the depth of focus of an imaging system. The coding element is an asymmetrical phase plate shape, for most applications in the form of a trefoil or a cubic polynomial. Phase plates with trefoil shape generate not only the desired amount of trefoil aberration but also spherical aberration. It has been recently shown that a wavefront coding based optical system shows high tolerance to spherical aberration for monochromatic images;however, the depth of focus is considerably shortened for color images. In this work, we will show how to modify the shape of a phase plate in order to optimize its performance for color imaging. The design parameters of the phase plate are obtained by minimizing a merit function by means of genetic algorithms developed for this purpose. The evaluation of the optical characteristics of the phase plates for a feedback with the optimization algorithm is obtained by Zemax. Results will be illustrated by numerical simulations of color images.

关键词： wavefront coding spherical aberration color imaging optimization genetic algorithms

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Distributed wavefront coding for wide angle imaging system

Distributed wavefront coding for wide angle imaging system

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Conference on Current Developments in Lens Design and Optical Engineering XII/Advances in Thin Film Coatings VII

作者： Lariviere-Bastien, Martin Zhang, Hu Thibault, Simon Univ Laval Dept Phys Genie Phys & Opt COPL Quebec City PQ G1V 0A6 Canada

ISBN: (纸本)9780819487384

The emerging paradigm of imaging systems, known as wavefront coding, which employs joint optimization of both the optical system and the digital post-processing system, has not only increased the degrees of design freedom but also brought several significant system-level benefits. The effectiveness of wavefront coding has been demonstrated by several proof-of-concept systems in the reduction of focus-related aberrations and extension of depth of focus. While previous research on wavefront coding was mainly targeted at imaging systems having a small or modest field of view (FOV), we present a preliminary study on wavefront coding applied to panoramic optical systems. Unlike traditional wavefront coding systems, which only require the constancy of the modulation transfer function (MTF) over an extended focus range, wavefront-coded panoramic systems particularly emphasize the mitigation of significant off-axis aberrations such as field curvature, coma, and astigmatism. The restrictions of using a traditional generalized cubic polynomial pupil phase mask for wide angle systems are studied in this paper. It is shown that a traditional approach can be used when the variation of the off-axis aberrations remains modest. Consequently, we propose to study how a distributed wavefront coding approach, where two surfaces are used for encoding the wavefront, can be applied to wide angle lenses. A few cases designed using Zemax are presented and discussed

关键词： wavefront coding wide angle panoramic phase mask

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Using wavefront coding in presence of non-symmetric aberrations

Using Wavefront Coding in presence of non-symmetric aberrati...

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11th Euro-American Workshop on Information Optics (WIO)

作者： Lariviere-Bastien, Martin Thibault, Simon Univ Laval Dept Phys Genie Phys & Opt Quebec City PQ G1K 7P4 Canada

ISBN: (纸本)9781467320009;9781467319980

wavefront coding is a hybrid technology designed to increase depth of field of conventional optics but it can also be used to compensate for other aberration and ease tolerancing. The goal of our research is to apply this technology to panoramic imager. Panoramic imagers suffer from an increase level of aberration due to the large field of view and it is also subject to a special tolerance process. They also typically have a wide variation of the point spread function (PSF) across the field of view and suffer from non-symmetric aberration like coma and astigmatism. To obtain the best result using wavefront coding, the PSF should be as invariant as possible over the whole field of view. Asymmetric phase masks, when used in systems having non-negligible asymmetric aberrations, generate variations in the final image quality. For that reason, a model that predicts the final image quality of wavefront coded system is needed. The possibility of using two surfaces for wavefront coding has been studied. The final results were analysed using a variance based image quality criterion. From these results, it is possible to optimize phase mask for panoramic imager and predict the resulting image quality.

关键词： component wavefront coding wide angle Panomorph

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Phase transfer function based method to alleviate image artifacts in wavefront coding imaging system

Phase transfer function based method to alleviate image arti...

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5th International Symposium on Photoelectronic Detection and Imaging (ISPDI) - Infrared Imaging and Applications

作者： Mo Xutao Wang Jinjiang Anhui Univ Technol Inst Image Engn Sch Math & Phys Maanshan 243002 Peoples R China

ISBN: (纸本)9780819497765

wavefront coding technique can extend the depth of filed (DOF) of the incoherent imaging system. Several rectangular separable phase masks (such as cubic type, exponential type, logarithmic type, sinusoidal type, rational type, et al) have been proposed and discussed, because they can extend the DOF up to ten times of the DOF of ordinary imaging system. But according to the research on them, researchers have pointed out that the images are damaged by the artifacts, which usually come from the non-linear phase transfer function (PTF) differences between the PTF used in the image restoration filter and the PTF related to real imaging condition. In order to alleviate the image artifacts in imaging systems with wavefront coding, an optimization model based on the PTF was proposed to make the PTF invariance with the defocus. Thereafter, an image restoration filter based on the average PTF in the designed depth of field was introduced along with the PTF-based optimization. The combination of the optimization and the image restoration proposed can alleviate the artifacts, which was confirmed by the imaging simulation of spoke target. The cubic phase mask (CPM) and exponential phase mask (EPM) were discussed as example.

关键词： wavefront coding phase transfer function phase mask image restoration optimization

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Hybrid optical-digital encryption system based on wavefront coding paradigm

Hybrid optical-digital encryption system based on wavefront ...

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Conference on Optical Pattern Recognition XXIII

作者： Konnik, Mikhail V. Univ Newcastle Sch Elect Engn & Comp Sci Callaghan NSW 2308 Australia

ISBN: (纸本)9780819490766

The wavefront coding is a widely used in the optical systems to compensate aberrations and increase the depth of field. This paper presents experimental results on application of the wavefront coding paradigm for data encryption. We use a synthesised diffractive optical element (DOE) to deliberately introduce a phase distortion during the images registration process to encode the acquired image. In this case, an optical convolution of the input image with the point spread function (PSF) of the DOE is registered. The encryption is performed optically, and is therefore is fast and secure. Since the introduced distortion is the same across the image, the decryption is performed digitally using deconvolution methods. However, due to noise and finite accuracy of a photosensor, the reconstructed image is degraded but still readable. The experimental results, which are presented in this paper, indicate that the proposed hybrid optical-digital system can be implemented as a portable device using inexpensive off-the-shelf components. We present the results of optical encryption and digital restoration with quantitative estimations of the images quality. Details of hardware optical implementation of the hybrid optical-digital encryption system are discussed.

关键词： wavefront coding optical encryption system digital decryption hybrid systems

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Study on depth of field of wavefront coding imaging system

Study on depth of field of wavefront coding imaging system

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Conference on Applications of Digital Image Processing XXXI

作者： Pan, Chao Chen, Jiabi Mang, Dawei Zhuang, Songlin Univ Shanghai Sci & Technol Coll Opt & Elect Informat Engn Shanghai 200093 Peoples R China

ISBN: (纸本)9780819472939

The wavefront coding imaging technology is a good approach of extending DOF (depth of field) of imaging optical system with an identical exit pupil. A phase mask being introduced in the exit pupil of the optical system makes the MTF of the system to be defocus-independent. As a result, the DOF of the system is extended without a loss of resolution. How much this technique can extend the DOF of optical system? It was shown by experimental and simulation results of some papers that a wavefront coding imaging system can make the DOF raise an order of magnitude. However, there is no theoretical analysis of DOF extension of wavefront coding technique up to now. In this paper, a special condition under which MTF of wavefront coding system is defocus-Independent is discovered by investigating the OTF of the wavefront coding imaging system with cubic phase mask. Based on the condition, an expression of the DOF of wavefront coding imaging system is obtained. The conclusion is verified by the simulation results.

关键词： wavefront coding field depth extending cubic phase mask optical transfer function modulation transfer function

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Low-cost wavefront coding using coma and a denoising-based deconvolution

Low-cost wavefront coding using coma and a denoising-based d...

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Conference on Electro-Optical and Infrared Systems - Technology and Applications IV

作者： Dorronsoro, Carlos Guerrero-Colon, Jose A. de la Fuente, Marta C. Infante, Jose M. Portilla, Javier Imatr Image Technol Madrid Spain Univ Granada Dept Comp Sci & Artificial Inteligence Granada Spain Indra Sistemas Aranjuez Madrid Spain Inst Opt Consejo Super Invest Cient Madrid Spain

ISBN: (纸本)9780819468956

wavefront coding (WFC) is a powerful hybrid optical-numerical technique for increasing the depth of focus of imaging systems. It is based on two components: (1) an optical phase element that codifies the wavefront, and (2) a numerical deconvolution algorithm that reconstructs the image. Traditionally, some sophisticated optical WFC designs have been used to obtain approximate focus-invariant point spread functions (PSFs). Instead, we present a simple and low cost solution, implemented on infrared (IR) cameras, which uses a decentred lens inducing coma as an adjustable and removable phase element. We have used an advanced deconvolution algorithm for the image reconstruction, which is very robust against high noise levels. These features allow its application to low cost imaging systems. We show encouraging preliminary results based on realistic simulations using optical PSFs and noise power spectral density (PSD) laboratory models of two IR imaging systems. Without induced optical phase, the reconstruction algorithm improves the image quality in all cases, but it performs poorly when there are both in and out-of-focus objects in the scene. When using our coding/decoding scheme with low-noise detectors, the proposed solution provides high quality and robust recovery even for severe defocus. As sensor noise increases, the image suffers a graceful degradation, its quality being still acceptable even when using highly noisy sensors, such as microbolometers. We have experienced that the amount of induced coma is a key design parameter: while it only slightly affects the in-focus image quality, it is determinant for the final depth of focus.

关键词： wavefront coding IR cameras coma image deconvolution image denoising image deblurring

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