Traditional zoom lens designs employ multiple moving lens elements to provide simultaneous control of focal length and focal plane. We present an example of a simplified and compact zoom lens design by employing a sin...
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ISBN:
(纸本)9780819473301
Traditional zoom lens designs employ multiple moving lens elements to provide simultaneous control of focal length and focal plane. We present an example of a simplified and compact zoom lens design by employing a single moving element to control only the focal length. In this zoom lens, wavefront coding is used to control the defocus. We describe the principles of operation with special attention to image processing. We simulate imaging and image restoration capabilities and present that the zoom lens provides high imaging quality.
Iris recognition can offer high-accuracy person recognition, particularly when the acquired iris image is well focused. However, in some practical scenarios, user cooperation may not be sufficient to acquire iris imag...
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Iris recognition can offer high-accuracy person recognition, particularly when the acquired iris image is well focused. However, in some practical scenarios, user cooperation may not be sufficient to acquire iris images in focus;therefore, iris recognition using camera systems with a large depth of field is very desirable. One approach to achieve extended depth of field is to use a wavefront-coding system as proposed by Dowski and Cathey, which uses a phase modulation mask. The conventional approach when using a camera system with such a phase mask is to restore the raw images acquired from the camera before feeding them into the iris recognition module. In this paper, we investigate the feasibility of skipping the image restoration step with minimal degradation in recognition performance while still increasing the depth of field of the whole system compared to an imaging system without a phase mask. By using a simulated wavefront-coded imagery, we present the results of two different iris recognition algorithms, namely, Daugman's iriscode and correlation-filter-based iris recognition, using more than 1000 iris images taken from the Iris Challenge Evaluation database. We carefully study the effect of an off-the-shelf phase mask on iris segmentation and iris matching, and finally, to better enable the use of unrestored wavefront-coded images, we design a custom phase mask by formulating an optimization problem. Our results suggest that, in exchange for some degradation in recognition performance at the best focus, we can increase the depth of field by a factor of about four ( over a conventional camera system without a phase mask) by carefully designing the phase masks.
By combining optical systems and image processing, wavefront coding can greatly expand the depth of focus and depth of field of optical systems. It has been widely used in iris detection, high-power microscopic object...
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ISBN:
(数字)9781510652095
ISBN:
(纸本)9781510652095;9781510652088
By combining optical systems and image processing, wavefront coding can greatly expand the depth of focus and depth of field of optical systems. It has been widely used in iris detection, high-power microscopic objective lens, infrared optical system athermalized, and so on. At present, the image restoration algorithms commonly used in wavefront coding are based on deconvolution, Wiener filtering, and so on. Although these algorithms can achieve an excellent image restoration effect, they will also bring boundary ringing effects and artifacts to the image. When the image is disturbed by strong noise, the restoration effect will also be seriously affected. To solve these problems, a wavefront coded image restoration algorithm based on compressed sensing is proposed in this paper. The strong data reconstruction ability of the compressed sensing restoration algorithm is used to restore the encoded image obtained by the wavefront coding system. This method can effectively suppress noise and reconstruct the image without artifact and boundary ringing effect. Through the comparison of simulation results, the effectiveness of the proposed method is verified.
wavefront coding (WFC) technique is typically used to compensate for optical aberrations related to defocus. An advantage of WFC are that the depth of field (DOF) will be increased and the weight and size of an optica...
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ISBN:
(数字)9781510620629
ISBN:
(纸本)9781510620629
wavefront coding (WFC) technique is typically used to compensate for optical aberrations related to defocus. An advantage of WFC are that the depth of field (DOF) will be increased and the weight and size of an optical system are reduced. In this work a WFC system is analyzed to extend the DOF of the microscope objective. The Point Spread Function (PSF) is used to modify in such a way that it is invariant to defocus in a range of axial distances. A liquid crystal display light modulator (LC SLM) in a 4f imaging system is used for the implementation of the phase masks (PM). LC SLM screens modulate both the amplitude and the phase of the input beam. This display allows a flexible implementation of different profiles of phase masks that are generated from different families of functions, this is because the parameters can be dynamically modified. In this document, we propose an experimental setup for extended DOF in optical microscopy. Experimental results are presented using a LC - SLM.
Simulated results demonstrate the impact of detector noise on the design of a broadband wavefront coded optical system. We conclude that noise must be included as a first-order design constraint in cubic phase-encoded...
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ISBN:
(纸本)9781628413786
Simulated results demonstrate the impact of detector noise on the design of a broadband wavefront coded optical system. We conclude that noise must be included as a first-order design constraint in cubic phase-encoded systems.
wavefront coding (WFC) uses a special aspheric optics and digital image processing to extend the depth of focus in imaging systems. An intermediate blurred image is generated by the spatial convolution of the image wi...
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ISBN:
(纸本)9781628412192
wavefront coding (WFC) uses a special aspheric optics and digital image processing to extend the depth of focus in imaging systems. An intermediate blurred image is generated by the spatial convolution of the image with the point spread function (PSF) of a cubic phase mask. Restoration tests are performed on an optically encoded image. The best option to restore an image is not always given by a deconvolution method using the PSF of the imaging system. Due to it is limited by the perfect PSF of the system. In this study, the restored image is given by a deconvolution method using the numerical PSF. As the quality of the image is depended of the pupil diameter and strength of the wfc phase plate, an optimization was achieved by means of measuring the decoded image contrast. Results shows a high resolution decoded image.
We present the results of the utilization of a Spatial Light Modulator Liquid Crystal Display for the implementation of wavefront codification procedures in all imaging system. The light modulator works in transmissio...
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ISBN:
(纸本)9780819473301
We present the results of the utilization of a Spatial Light Modulator Liquid Crystal Display for the implementation of wavefront codification procedures in all imaging system. The light modulator works in transmission mode at the pupil of the instrument. The main disadvantage is that the procedure implies a calibration of the device as well as an inherent image processing. The more interesting feature we can obtain is the versatility related to the use of all electronic device at the pupil, as compared with conventional (fixed) manufactured ones.
wavefront coding is a new method to extend the depth of field, which combines optical design and signal processing together. By using optical design software ZEMAX, we designed a practical wavefront coded imaging syst...
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ISBN:
(数字)9781510607675
ISBN:
(纸本)9781510607675
wavefront coding is a new method to extend the depth of field, which combines optical design and signal processing together. By using optical design software ZEMAX, we designed a practical wavefront coded imaging system based on a conventional Cooke triplet system. Unlike conventional optical system, the wavefront of this new system is modulated by a specially designed phase mask, which makes the point spread function (PSF) of optical system not sensitive to defocus. Therefore, a series of same blurred images obtained at the image plane. In addition, the optical transfer function (OTF) of the wavefront coded imaging system is independent of focus, which is nearly constant with misfocus and has no regions of zeros. All object information can be completely recovered through digital filtering at different defocus positions. The focus invariance of MTF is selected as merit function in this design. And the coefficients of phase mask are set as optimization goals. Compared to conventional optical system, wavefront coded imaging system obtains better quality images under different object distances. Some deficiencies appear in the restored images due to the influence of digital filtering algorithm, which are also analyzed in this paper. The depth of field of the designed wavefront coded imaging system is about 28 times larger than initial optical system, while keeping higher optical power and resolution at the image plane.
wavefront coding technology can extend the depth of field of the iris imaging system, but the iris image obtained through the system is coded and blurred and can't be used for the recognition algorithm directly. T...
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ISBN:
(纸本)9780819488411
wavefront coding technology can extend the depth of field of the iris imaging system, but the iris image obtained through the system is coded and blurred and can't be used for the recognition algorithm directly. The paper presents a fuzzy iris image restoration method used in the wavefront coding system. After the restoration, the images can be used for the following processing. Firstly, the wavefront coded imaging system is simulated and the optical parameter is analyzed, through the simulation we can get the system's point spread function (PSF). Secondly, using the blurred iris image and PSF to do a blind restoration to estimate a appropriate PSFe. Finally, based on the return value PSFe of PSF, applying the regularization filter on the blurred image. Experimental results show that the proposed method is simple and has fast processing speed. Compared with the traditional restoration algorithms of Wiener filtering and Lucy-Richardson filtering, the recovery image that got through the regularization filtering is the most similar with the original iris image.
A novel design of a wavefront coded compact camera system with liquid lens is presented. The point spread function must remain practically constant over a wide range of defocus in order to create an image which is sha...
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ISBN:
(纸本)9780819472816
A novel design of a wavefront coded compact camera system with liquid lens is presented. The point spread function must remain practically constant over a wide range of defocus in order to create an image which is sharp over a large depth of field. Therefore, the trade-off between the effect of extended depth of field and reduction in the signal to noise ratio of the restored image become critical. By combining liquid lens and wavefront coding, the system can deliver much greater depth of field without the restoration problems caused by the similarity of point spread function. This could improve the overall image performance.
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