• 제어로봇시스템학회논문지
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• 제12권4호
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• pp.364-370
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• 2006

Optical coherence tomography (OCT) is high resolution medical imaging system which is obtaining image inside biological objects with non-destructive method. OCT system is based on Michelson interferometer with a reciprocating mirror in the reference arm and a biological object in the sample arm. The obtained OCT image suffers from a granular or mottled image, called speckle. Speckle is caused by random interferences between reflected coherence waves. In this paper, we propose effective speckle reduction method that uses wavelet transform. With wavelet domain image, sub-windowing and thresholding are performed. Finally, speckle reduction experiments for Misgurnus mizolepis skin and rat eye images are shown.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.2459-2463
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• 2005

Optical coherence tomography (OCT) is high resolution medical imaging system which is obtaining image inside biological objects with non-destructive method. OCT system is based on Michelson interferometer with a reciprocating mirror in the reference arm and a biological object in the sample arm. The obtained OCT image suffers from a granular or mottled image, called speckle. Speckle is caused by random interferences between reflected coherence waves. In this paper, we propose effective speckle reduction method that uses wavelet transform. With wavelet domain image, sub-windowing and thresholding are performed. Finally, speckle reduction experiments for Misgurnus mizolepis skin and rat eye images are shown.

• 정보저장시스템학회논문집
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• 제10권2호
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• pp.55-60
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• 2014

Laser projector has many advantages of high brightness, high resolution and small size, but the huge drawback of image degradation called speckle which generated by coherence of laser and roughness of surface interrupts their general use. There are many methods to reduce speckle pattern, but they need effective optical systems to realize display to the far field with huge volume. We designed speckle reduction element by using microlens with controlled curvature to reduce spatial coherence. Vibration element was also applied to reduce temporal coherence which considered response time of eye. Designed element was fabricated by simple reflow method and imprinting method. From the results, the fabricated element performed 48.33% of speckle reduction efficiency and 41.29% of optical efficiency with a single doublet lens.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.303-307
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• 2002

Although Synthetic Aperture Radar(SAR) is a very powerful and attractive tool, automatic interpretation of SAR images is extremely difficult because of several reason. Spatially, speckle noise reduction in SAR images is important step to interpret the SAR image at the preprocessing step. The speckle noise in SAR images is modeled to be multiplicative, and therefore, a signal-dependent noise. So, it has deflated many image-denoising algorithms that are based on additive noise model. In this paper, we propose an adaptive wavelet shrinkage method for speckle noise reduction in SAR images by analyzing the high frequency level in detail. We first decompose minutely the high frequency level to analyze the noise level. And then, we determine the weighting threshold value per the level, and layer. Finally, using those weighting threshold, we produce the efficient wavelet shrinkage method. So, this method not only reduces the speckle noise, but also preserves image detail and sharpness.

• Journal of information and communication convergence engineering
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• 제7권4호
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• pp.535-538
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• 2009

Speckle noise reduction for ultrasound CT image using morphological adaptive median filtering based on edge preservation is presented in this paper. Speckle noise is multiplicative feature and causes ultrasound image to degrade widely from transducer. An input image is classified into edge region and homogeneous region in preprocessing. The speckle is reduced by morphological operation on the 2D gray scale by using convolution and correlation, and edges are preserved. The adaptive median is processed to reduce an impulse noise to preserve edges. As the result, MAM of the proposed method enhances the image to about 10% in comparison with Winner filter by Edge Preservation Index and PSNR, and 10% to only adaptive median filtering.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 추계학술대회
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• pp.329-332
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• 2009

Speckle noise reduction for ultrasound CT image using morphological adaptive median filtering based on edge preservation is presented in this paper. Speckle noise is multiplicative feature and causes ultrasound image to degrade widely from transducer. An input image is classified into edge region and homogeneous region in preprocessing. The speckle is reduced by morphological operation on the 2D gray scale by using convolution and correlation, and edges are preserved. The adaptive median is processed to reduce an impulse noise. As the result the proposed method enhances the image to about 20% in comparison with Winer filter by Edge Preservation Index and PSNR.

• Journal of Welding and Joining
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• 제17권6호
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• pp.100-107
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• 1999

In this paper, we deal with the speckle noise reduction and parameter estimation of ultrasonic NDT(non-destructive test) signals obtained during weld inspection of piping. The overall approach consists of three major steps, namely, speckle noise analysis, proposition of wavelet domain AR(autoregressive) model and flaw detection by proposed model parameter. The data are first processed whereby signals obtained using vertical and angle beam transducer. Correlation properties of speckle noise are then analyzed using multiresolution analysis in wavelet domain. The parameter estimation curve obtained using the proposed model is classified a flaw in weld region where is contaminated by severe speckle noise and also clear flaw signal is obtained through CA-CFAR threshold estimator that is a nonlinear post-processing method for removing the noise from reconstructed ultrasonic signal.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.175-182
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• 1998

SAR 영상은 speckle 잡음의 multiplicative 특성으로 인해 영상 해석에 많은 제약을 받고 있다. Speckle 잡음을 제거하기 위한 방법은 크게 여러 개의 독립 영상을 multi-looks 처리 방법과 디지털 영상 처리 기술을 이용하는 방법으로 speckle 잡음 특성에 따른 비선형필터의 적용이다. 본 연구에서는 국지적 통계 자료를 이용하는 LEE와 Refined LEE 필터 그리고 speckle 자체의 통계 특성을 이용하는 EPOS(Edge Preserving Optimal Speckle)필터를 이용하여 speckle 잡음을 제거하여 SAR 영상의 화질을 개선하고 그 결과를 기존의 mean과 median 필터와 비교하였다.

• 대한의용생체공학회:의공학회지
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• 제29권2호
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• pp.122-131
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• 2008

For B-mode ultrasound images, we propose an image enhancement algorithm based on a multi-resolution approach, which consists of edge enhancing and noise reducing procedures. Edge enhancement processing is applied sequentially to coarse-to-fine resolution images obtained from wavelet-transformed data. In each resolution, the structural features of each pixel are examined through eigen analysis. Then, if a pixel belongs to an edge region, we perform two-step filtering: that is, directional smoothing is conducted along the tangential direction of the edge to improve continuity and directional sharpening is conducted along the normal direction to enhance the contrast. In addition, speckle noise is alleviated by proper attenuation of the wavelet coefficients of the homogeneous regions at each band. This region-based speckle-reduction scheme is differentiated from other methods that are based on the magnitude statistics of the wavelet coefficients. The proposed algorithm enhances edges regardless of changes in the resolution of an image, and the algorithm efficiently reduces speckle noise without affecting the sharpness of the edge. Hence, compared with existing algorithms, the proposed algorithm considerably improves the subjective image quality without providing any noticeable artifacts.

• Journal of the Optical Society of Korea
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• 제12권3호
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• pp.126-130
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• 2008

We propose and experimentally demonstrate an effective method to reduce near-field speckle noise at the output of a 50 ${\mu}m$ graded index multimode fiber using a short cylindrical piezoelectric transducer(PZT) vibrating in the radial direction. The fiber was coiled as tightly as possible around the mandrel of the PZT and a periodic stretching effect was caused by the radial oscillations of the actuator. The output of the optical fiber using the He-Ne laser source was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded into 256 levels in the selected area and by calculating standard deviation and mean value of the intensity, we could measure the speckle contrast and vibration effect quantitatively with reduction ratio of pixels and line profile of the illuminated region. It was clearly observed that the characteristics of the speckle pattern in the vibration-on state were significantly improved over that of the vibration-off state due to time-averaged smoothing.