共查询到20条相似文献,搜索用时 15 毫秒
1.
Akshay Sharma Gyanendra Sheoran Z.A. Jaffery Moinuddin 《Optics and Lasers in Engineering》2008,46(1):42-47
The basic problem in optical and digital holography is the presence of speckle noise in the reconstruction process, which reduces the signal-to-noise ratio (SNR). The presence of speckle noise is serious drawback in optical and digital holography since it substantially reduces the SNR in the reconstructed image. In this paper, we present wavelet filtering to improve SNR in the reconstructed images from digital holograms. Experimental results are presented. 相似文献
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Xiao-ou Cai 《Optik》2014
As one of the most important 3-D display technique, reduction of speckle noise in the reconstructed image of digital holography should be grounded on the digital hologram itself. Based on the whole process of the recording and reconstruction of digital holography, the optical distributions of recorded object and reconstructed image of digital holography have been studied. It has been proposed that the root formation cause of speckle noise in its reconstructed image is the speckle noise formed on the recorded object surface when illuminated by coherent light because of its optical roughness. A novel approach has been presented to reduce speckle noise in digital holography by changing the interference structure of hologram itself. First, by reducing the speckle noise in the reconstructed image, the distribution of ideal reconstruction light with reduced speckle noise is acquired. Then in turn, taking the ideal reconstruction light with reduced speckle noise as ideal object light, a new hologram can be rebuilt, which can reconstruct the ideal object light. The experimental results are given to confirm the proposed method. Therefore, it offers a brand-new thought and practical way to reduce the speckle noise in the reconstructed image of digital holography. 相似文献
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Based on the whole process of the recording and reconstruction of digital holography, we study the formation cause of speckle noise in its reconstructed image and acquire the conclusion that the small size of hologram aperture diffraction aggravates the speckle noise of reconstructed image and the speckle noise has been one of primary noise sources in the reconstruction process. In order to reduce the speckle noise resulting from little hologram aperture diffraction, we set an appropriate aperture function matching the recording parameter and aperture size of hologram and deconvolve the reconstructed image with it. The validity has been proved in theory and experiment. Therefore, it offers a brand-new thought and practical way to reduce the speckle noise in the reconstructed image of digital holography. 相似文献
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为了解决在数字散斑干涉技术测量时,散斑干涉相位条纹图像中大量噪声对相位解包裹结果和精度产生严重影响的问题,介绍了一种条纹正余弦分解和频域低通滤波结合的方法,实现了散斑干涉相位条纹图的高精度滤波。该方法的基本思路是在对相位图像进行滤波处理前,先将相位图通过正余弦函数进行映射转换成两幅图,分别经过频域滤波,然后再合成为相位图。这种分解频域滤波方法可以在滤波的同时,有效保留相位跳变信息。实验结果表明:与传统的图像降噪方法相比,该方法能够在保留图像“尖峰”信息的基础上,较好地滤除图像中的散斑噪声,方法简单有效,有效解决了传统滤波方法应用在相位条纹图中,相图灰度信息丢失10%~40%的问题。 相似文献
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An integrated method based on optical and digital image processing is presented to suppress speckle in digital holography. A spatial light modulator is adopted to introduce random phases to the illuminating beam. Multiple holograms are reconstructed and superimposed, and the intensity is averaged to smooth the noise. The adaptive algorithm based on the nonlocal means is designed to further suppress the speckle. The presented method is compared with other methods reduction is improved, and the proposed method is effective The experimental results show that speckle and feasible. 相似文献
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Xiao-ou Cai 《Optik》2010,121(4):394-17959
Based on the whole process of recording and reconstruction of digital holography, we study the formation causes of speckle noise in the reconstructed image and its characteristics. And we reach the conclusions that the little hologram aperture diffraction aggravates the speckle noise and the speckle noise in the reconstructed image is a kind of multiplicative noise. Serving as the basis of these features, we propose the reduction technique for speckle noise. Firstly, we set an appropriate aperture function matching the recording parameter and an aperture size of hologram and deconvolve the reconstructed image of the hologram with it. Secondly, we converted the multiplicative noise into additive noise by means of homomorphic transform and realize the separation of signal and noise. Thirdly, we applied the Wiener filtering to reduce the additive noise. Finally, we carried out the inverse transformation. The proposed reduction technique is illustrated with experimental results. Therefore, the paper offers a brand-new thought and practical way of reducing the speckle noise in the reconstructed image of digital holography. 相似文献
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This paper presents a method for recording and reconstructing high-quality digital color holographic images. The synthetic aperture technique is used to improve the resolution of the reconstructed image and also reduce the speckle size in the reconstruction plane. Subsequently, the multiple reference wave technique is used to suppress speckle noise in the reconstructed color holographic image by superposing speckle fields with different distributions. The final high-quality color holographic image is obtained due to the resolution improvement and speckle noise reduction achieved by the two techniques. Our method has potential applications in the digital color holographic displays. 相似文献
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在数字全息成像中,散斑噪声严重影响了再现像的信噪比和成像分辨率,因此为了提高数字全息成像质量,迫切需要抑制再现像的散斑噪声.分析并给出了矩形散射光斑的强度协方差,定量计算了特定实验条件下产生退相关散斑图样的最小角度差.结合透镜的性质设计并搭建了多角度无透镜傅里叶变换数字全息成像系统,利用光纤端面在透镜焦平面的二维机械移动代替传统反射镜的旋转,使照明光束在不改变照明位置和大小的同时,可任意改变光束方向.移动光纤端面使多角度照明满足最小角度差,获取了81幅数字全息图.利用单次快速傅里叶逆变换实现数值再现,对多幅再现像的强度像求平均,实验结果表明散斑对比度降低为单幅再现像的14.6%,使图像信噪比提高了6.9倍.该抑制散斑的多角度数字全息成像方法有效的抑制了散斑噪声,且成像光路结构简单,可操作性强. 相似文献
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在数字全息测量记录过程中,其所记录的全息图易受到散斑噪声的污染造成分辨率下降,同时也严重影响数字全息再现的效果,因此研究适用于数字全息技术中散斑滤波的算法具有重要的实用价值。介绍了中值滤波、Lee滤波、Kuan滤波和SUSAN滤波这四种常用的散斑滤波算法,并将它们运用于数字全息实验所记录图像和数字再现图像的散斑噪声滤波处理中,然后对这四种算法的处理结果进行评价。结果表明,在数字全息技术中使用SUSAN滤波算法进行处理,既明显抑制了散斑噪声,又有效保证了再现图像信息的完整性。 相似文献
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An improved method of using a selective spatial-domain mask to reduce speckle noise in digital holography is proposed.The sub-holograms are obtained from the original hologram filtered by the binary masks including a shifting aperture for being reconstructed. Normally, the speckle patterns of these sub-reconstructed images are different. The speckle intensity of the final reconstructed image is suppressed by averaging the favorable sub-reconstructed images which are selected based on the most optimal pixel intensity sub-range in the sub-holograms. Compared with the conventional spatial-domain mask method, the proposed method not only reduces the speckle noise more effectively with fewer sub-reconstructed images,but also reduces the redundant information used in the reconstruction process. 相似文献
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Velocity and density field measurements based on image processing of laser speckle or pseudo-speckle pattern have been developed. Laser speckle velocimetry (LSV) or white-light speckle velocimetry (WSV), which corresponds to a high-image-density PIV, gives a local velocity vector map or whole field velocity contour map of a two-dimensional flow field seeded densely with fine particles. This technique has an advantage in high-speed flow measurement without limit of frame rate except for directional ambiguity. New techniques of laser speckle photography and laser speckle interferometry by means of digital image processing have been developed recently for density field measurements. In laser speckle photography, a local density gradient vector map is reconstructed by cross-correlation evaluation between the reference and the object speckle patterns. In laser speckle interferometry, an equi-density contour map is reconstructed by image subtraction between the reference and the object interferometric speckle patterns. 相似文献
13.
Freddy Alberto Monroy 《Optik》2010,121(22):2049-2052
Experimental features such as wavelength, camera specifications and reconstruction distance determine the theoretical limit for lateral resolution in digital holography. However, the actual experimental resolution limit is about 50% below such theoretical limit due to the high-contrast speckle noise presented in the reconstructed holograms. Recently, a technique has been introduced to reduce the contrast of speckle noise that is based on the superposition of uncorrelated hologram reconstructions of the same static object [5] (Garcia-Sucerquia et al., 2006). By this approach of reducing the contrast of the speckle noise, it is experimentally shown that an improvement of the order of 50% can be reached when 100 reconstructed images are superimposed. 相似文献
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针对在成像物体没有超出散射介质记忆效应范围的情况下,提出一种结合数字离轴全息术减少散射介质成像中散斑自相关噪声的方法。当成像目标经过散射介质时,使用自相关技术结合相位恢复算法能够从散斑中重建成像目标。但在实际成像的过程中,为了有效抑制环境噪声和热噪声等对重建效果的影响,设计利用离轴全息中的相移法消除噪声项中静态噪声项的干扰,再利用散斑自相关与相位恢复算法重建去噪后效果更好的成像目标。采用结构相似度对重建效果进行定量评估,仿真结果表明对于给出的成像目标,去噪前后的结构相似度从0.8796提高到0.9875,验证了该方法的有效性。说明所提出的方法能够改善散斑自相关法重建效果。 相似文献
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Controllable experimental features such as wavelength, camera’s specifications and reconstruction distance, determine the theoretical limit for lateral resolution in digital holography; however, due to the speckle noise associated to any coherent imaging system it is not possible to reach this theoretical limit. In this paper, a quantitative study the lateral resolution for digital holography under the effect the speckle noise is carried out. It is shown that by reducing the contrast of the speckle noise the resolution capabilities of digital holography are improved; the signal-to-noise ratio of the reconstructed holograms is the metric use to quantitatively assess the reached resolution in the holographic experiments. 相似文献
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During the reconstruction of a digital hologram, the reconstructed image is usually degraded by speckle noise, which makes it hard to observe the original object pattern. In this paper, a new reconstructed image enhancement method is proposed, which first reduces the speckle noise using an adaptive Gaussian filter, then calculates the high frequencies that belong to the object pattern based on a frequency extrapolation strategy. The proposed frequency extrapolation first calculates the frequency spectrum of the Fourier-filtered image, which is originally reconstructed from the +1 order of the hologram, and then gives the initial parameters for an iterative solution. The analytic iteration is implemented by continuous gradient threshold convergence to estimate the image level and vertical gradient information. The predicted spectrum is acquired through the analytical iteration of the original spectrum and gradient spectrum analysis. Finally, the reconstructed spectrum of the restoration image is acquired from the synthetic correction of the original spectrum using the predicted gradient spectrum. We conducted our experiment very close to the diffraction limit and used low-quality equipment to prove the feasibility of our method. Detailed analysis and figure demonstrations are presented in the paper. 相似文献
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A new method of using time-averaged digital speckle pattern interferometry for the quantitative measurement of vibration amplitude was developed. Signal processing techniques especially the Hilbert transformation for quantitative evaluation of the Bessel fringes obtained in time-averaged digital speckle pattern interferometry were explored. The quadrature signal after Hilbert transformation is equivalent to a 90° phase-shifted interferogram for a monotonically increasing or decreasing phase function. An algorithm was developed for Bessel fringe contrast enhancement and phase extraction. The techniques were tested numerically and experimentally. Sub-fringe quantification of the time-averaged vibration fringes is realised with the proposed method. Compared with the commonly used phase shift method which requires a minimum of two images for image processing, this method requires only one fringe pattern for data extraction. 相似文献