Speckle Elimination Research Articles

Redundant speckle elimination in digital holography with the Gauss window function

Digital Holography (DH) is a popular and practical technology for recording the complex-valued information of the object field. However, speckle, caused by the coherent light, greatly reduces the quality of the reconstructed image. In this paper, a speckle-suppression algorithm called Gauss speckle elimination mask (GSEM) that only needs a single-shot DH is proposed. This method utilizes the Gauss window function to extract the sub-holograms. Besides, the gray value compensation is proposed in this method for restoring the grayscale distribution. All sub-holograms are operated by the gray value compensation, then a new stack of sub-reconstructed images is acquired. The output compounded by this stack of sub-reconstructed images avoids the additional noise caused by the ringing effect. It could be shown in this paper that this method has a better performance in speckle-suppression while maintaining the image contrast.

RPE layer detection and baseline estimation using statistical methods and randomization for classification of AMD from retinal OCT

Background and Objective: Age-related macular degeneration (AMD) is a condition of the eye that affects the aged people. Optical coherence tomography (OCT) is a diagnostic tool capable of analyzing and identifying the disease affected retinal layers with high resolution. The objective of this work is to extract the retinal pigment epithelium (RPE) layer and the baseline (natural eye curvature, particular to every patient) from retinal spectral-domain OCT (SD-OCT) images. It uses them to find the height of drusen (abnormalities) in the RPE layer and classify it as AMD or normal.Methods: In the proposed work, the contrast enhancement based adaptive denoising technique is used for speckle elimination. Pixel grouping and iterative elimination based on the knowledge of typical layer intensities and positions are used to obtain the RPE layer. Using this estimate, randomization techniques are employed, followed by polynomial fitting and drusen removal to arrive at a baseline estimate. The classification is based on the drusen height obtained by taking the difference between the RPE and baseline levels. We have used a patient, wise classification approach where a patient is classified diseased if more than a threshold number of patient images have drusen of more than a certain height. Since all slices of an affected patient will not show drusen, we are justified in adopting this technique.Results: The proposed method is tested on a public data set of 2130 images/slices, which belonged to 30 patient volumes (15 AMD and 15 Normal) and achieved an overall accuracy of 96.66%, with no false positives. In comparison with existing works, the proposed method achieved higher overall accuracy and a better baseline estimate.Conclusions: The proposed work focuses on AMD/normal classification using a statistical approach. It does not require any training. The proposed method modifies the motion restoration paradigm to obtain an application-specific denoising algorithm. The existing RPE detection algorithm is modified significantly to make it robust and applicable even to images where the RPE is not very evident/there is a significant amount of perforations (drusen). The baseline estimation algorithm employs a powerful combination of randomization, iterative polynomial fitting, and pixel elimination in contrast to mere fitting techniques. The main highlight of this work is, it achieved an exact estimation of the baseline in the retinal image compared to the existing methods.

Despeckling method of ultrasound images using closed-form shrinkage function based on cauchy distribution in wavelet domain

Speckle suppression and elimination are very important to improve the visual quality of ultrasound image and the diagnostic ability of the diseases. An effective technique of image denoising based on discrete wavelet transform is to employ a Bayesian maximum a posteriori (MAP) estimator. To suppress and remove the speckle noise using MAP estimator effectively, it must assign correctly the shrinkage function based on appropriate probability density functions (PDFs) for the wavelet coefficients of logarithmically transformed noise-free ultrasound image and speckle noise. In this paper, we introduce a new closed-form shrinkage function that is an analytical solution of a Bayesian MAP estimator for despeckling of the ultrasound images effectively in wavelet domain. We employ a Cauchy prior and Gaussian PDF to model the wavelet coefficients of logarithmically transformed noise-free ultrasound image and speckle noise, respectively. Firstly, we derive the CauchyShrinkGMAP that is a closed-form shrinkage function. In addition, we estimate the noise variance and parameter of MAP estimator. Next, we evaluate the despeckling performance of wavelet image denoising method using the CauchyShrinkGMAP compared to various despeckling method using median and Wiener filters, hard and soft thresholding and GaussShrinkGMAP and MCMAP3N shrinkage function. The experiment results show that PSNR of new closed-form shrinkage function is highest, MSE is smallest, and the correlation coefficient ([Formula: see text]) and SSIM are closer to one than the other existing image denoising methods for noisy synthetic ultrasound images at different speckle noise levels. Also, experiment results show that ENL of new closed-form shrinkage function is highest and that of EN and SD is smallest than the other existing image denoising methods for noisy real ultrasound image.

Single-shot speckle reduction by elimination of redundant speckle patterns in digital holography.

Speckle reduction is a crucial technique, since the presence of speckle disturbs the quality of the reconstruction in digital holography. In this paper, we present a redundant speckle elimination method to suppress the speckle noise. For the same position in each of the reconstructed sub-images, we consider pixels with the same gray value as information with the same speckle distribution. Therefore, a speckle-suppressed gray value can be obtained by extracting pixels with different gray values and then averaging. Through theoretical analysis and experiments, we demonstrate that speckle contrast can be decreased significantly by using the proposed method. Moreover, we show that the despeckle strength of the proposed method highly depends on the number of binary masks. These results indicate the potential of the proposed method for various applications.

Quantification of the effects of time-varying speckle patterns on speckle images using a modified speckle influence degree method

Numerous methods that generate time-varying speckle patterns have been used unsuccessfully to eliminate speckle. In this study, the speckle influence degree (SID) method is used in conjunction with a measurement system that emulates the human eyes. Time-varying speckle patterns are generated at different velocities, whereby the correlation degree between the speckle patterns, the correlation time, and SID, are calculated as a function of velocity. It is shown that the correlation time is 6 ms and SID is reduced to 6.4% when the velocity is increased up to 40μm∕ms. Further, when a chip motor with a velocity of 286μm∕ms is used to modulate speckle patterns, the correlation time and SID are reduced to 1 ms and 3.2%, respectively. Based on these results, the mechanism of time-varying speckle patterns is quantified for the first time, laying a scientific basis for proposing innovative methods of speckle elimination.

Speckle modulation enables high-resolution wide-field human brain tumor margin detection and in vivo murine neuroimaging

Current in vivo neuroimaging techniques provide limited field of view or spatial resolution and often require exogenous contrast. These limitations prohibit detailed structural imaging across wide fields of view and hinder intraoperative tumor margin detection. Here we present a novel neuroimaging technique, speckle-modulating optical coherence tomography (SM-OCT), which allows us to image the brains of live mice and ex vivo human samples with unprecedented resolution and wide field of view using only endogenous contrast. The increased visibility provided by speckle elimination reveals white matter fascicles and cortical layer architecture in brains of live mice. To our knowledge, the data reported herein represents the highest resolution imaging of murine white matter structure achieved in vivo across a wide field of view of several millimeters. When applied to an orthotopic murine glioblastoma xenograft model, SM-OCT readily identifies brain tumor margins with resolution of approximately 10 μm. SM-OCT of ex vivo human temporal lobe tissue reveals fine structures including cortical layers and myelinated axons. Finally, when applied to an ex vivo sample of a low-grade glioma resection margin, SM-OCT is able to resolve the brain tumor margin. Based on these findings, SM-OCT represents a novel approach for intraoperative tumor margin detection and in vivo neuroimaging.

Problems of Bad Contrast in Conventional Microscopy Solution and Speckle Elimination with a Laser Fourier Holographic Microscope

The problem of bad contrast in conventional microscopy is well-known and was solved in part by colouring the samples. It is shown theoretically that a laser Fourier holographic microscope produces images undisturbed by speckle-noise. A laser holographic microscope (LHM) is investigated experimentally. The instrument uses visible radiation of λ = 0.514 µm, Mach – Zehnder scheme optical setup, and CCD detector of the hologram. Images are reconstructed digitally. The standard slide of Parascaris Univalens Iarva (ascaris) is studied without any drying as for electron microscope. Comparison of the pictures of the same ascaris cell, observed by the LHM and high-quality Nikon conventional optical microscope with immersion oil and green filter indicates dramatically different contrast. The ultrahigh contrast of the LHM gives much more micromorphological information.

Efficient noise averaging in color holography by integration on shifted Fourier spectra

Modern holography is dealing mainly with the speckle noise and computational complexity. Reaching a compromise between the computational complexity (computing time) and quality of obtained images is required. This leads to a need to obtain a simple method of noise suppression with low computation complexity. An improved efficient projection of color images is presented. It uses a time averaging of intensity patterns reconstructed from the same Fourier hologram with lateral shifting in x and y direction. We try to establish the optimal step of shifting the Fourier spectra in both directions for each of the primary colors. Full Text: PDF References M. Makowski, Minimized speckle noise in lens-less holographic projection by pixel separation, Opt. Express 21, 29205-29216 (2013). CrossRef M. Makowski, A. Siemion, I. Ducin, K. Kakarenko, M. Sypek, A.M Siemion, J. Suszek, D. Wojnowski, Z. Jaroszewicz, A. Kolodziejczyk, Complex light modulation for lensless image Chin. Opt. Lett. 9, 120008 (2011). CrossRef L. Golan and S. Shoham, Speckle elimination using shift-averaging in high-rate holographic projection, Opt. Express 17, 1330-1339 (2009) CrossRef R. W. Gerchberg, and W. O. Saxton, A practical algorithm for the determination of phase from image and diffraction plane pictures, Optik (Stuttg.) 35, 237–246 (1972). A. Czerwinski, K. Kakarenko, M. Sypek, M. Makowski, I. Ducin, J. Suszek, A. Kolodziejczyk, J. Bomba, Modeling of the optical system illuminated by quasi-monochromatic spatially incoherent light: New numerical approach, Opt. Letters 37, 4723-4 (2012). CrossRef T. Shimobaba, T. Ito, N. Masuda, Y. Ichihashi, and N. Takada, Fast calculation of computer-generated-hologram on AMD HD5000 series GPU and OpenCL, Opt. Express 18, 9955-9960 (2010). CrossRef T. Shimobaba, Y. Sato, J. Miura, M. Takenouchi, and T. Ito, Real-time digital holographic microscopy using the graphic processing unit, Opt. Express 16, 11776-11781 (2008). CrossRef

Speckle elimination using shift-averaging in high-rate holographic projection

Speckle is a major source of noise in holographic projection. Time averaging of multiple holograms may be used to reduce speckle contrast, but multiple holograms must be calculated per each frame, costing in computational power. We show that a single hologram may be used to generate a fully speckle-free reconstruction, by cyclic shifting and time averaging. We demonstrate the concept experimentally, and discuss its application for high-rate holographic projection systems.

Control of variable structure elements in adaptive mathematical morphology for boundary enhancement of ultrasound images

AbstractThis paper discusses boundary enhancement function for adaptive morphology using variable structuring elements. The mechanism for boundary enhancement is quantitatively described. A method is proposed for setting the definition domain for the structuring elements and controlling their values, which is effective regarding boundary enhancement and speckle reduction in ultrasound images. It is shown that by controlling the value of the structuring element so that it is large near the boundary and small in other areas of the image, boundary enhancement and speckle elimination can be performed simultaneously, using the opening operation and closing operation. The spatial resolution and statistical properties of the speckle intensity in the ultrasound image are utilized to set these functions automatically on the basis of information on the object image. The effectiveness of the proposed method is demonstrated by a quantitative evaluation of a numerical phantom created in a computer simulation and in an application to boundary extraction from a real biological ultrasound image. It is shown that the performance of the proposed method in speckle reduction and boundary enhancement is better than that of the conventional method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 87(11): 20–33, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20117

Road vectors update using SAR imagery: a snake-based method

The paper presents an approach for roads detection based on synthetic aperture radar (SAR) images and road databases. The vectors provided by the database are refined using active contours (snakes). In this framework, we firstly develop a restoration filter based on the frost filter achieving an acceptable compromise between speckle elimination and lines preserving. This is followed by a line plausibility calculation step which is used to deform the snake from its initial location toward the final solution. The snake is reformulated using finite elements method. The setting of the snake parameters is not an obvious problem especially when they are tuned by trial-and-error process. We propose a new automatic computational rule for the snake parameters. Our approach is validated by a series of tests on synthetic and SAR images.

Diffraction response of a low-temperature-grown photorefractive multiple quantum well modulator

The transient diffraction response of a low-temperature-grown (LTG) photorefractive multiple quantum well (MQW) spatial light modulator (SLM) is studied experimentally as a function of the frequency and the on/off ratio of a single-sided applied voltage when a grating is written using a continuous-wave sinusoidal illumination. LTG MQW modulators have high spatial resolution, but their diffraction efficiency and speed are reduced. By varying the on/off ratio of the applied voltage, it is shown that the frequency response of the SLM can be optimized while maintaining its high spatial resolution. The flatness of the frequency response with respect to the peak diffracted signal is thus shown to increase by an order of magnitude. By temporally gating the diffracted signal, low and bandpass filtering capabilities of the SLM are experimentally demonstrated for applications such as speckle elimination and novelty filtering. When the diffracted signal is measured over an adjustable time window, it is shown that high frame rate operations in integrated optoelectronic systems can be achieved. A numerical model that includes the effect of high trap densities on the space-charge dynamics is developed. It is shown that the space-charge field grows nonuniformly along the MQW growth direction with the largest modulation in lateral field occurring only near the entrance face of the incident light, thus accounting partially for the low diffraction efficiency of LTG materials.

Improved random spatial phase modulation for speckle elimination

An improved version of the random spatial phase modulator (RSPM) reported recently by one of us is described. Using the improved RSPM, a theoretical value of the SNR of several thousand can be achieved. Experimental results are presented verifying that speckle can be completely eliminated using RSPM. The measured SNR exceeds 100, and there is no visually detectable difference between images obtained with RSPM laser light and those with white light even for an optical system of f/600. The effective decorrelation distances for different diffusers and their dependence on the aperture of the RSPM are investigated. An application of RSPM to coherent spatial filtering is demonstrated.

Speckle-free rear-projection screen using two close screens in slow relative motion

Speckle in rear-projection screens, such as those used in microfiche viewers, reduces resolution and can cause viewer fatigue. Many speckle-reduction techniques have been tried with varying degrees of success, including rapid movement of a single screen in its plane, the use of two stationary spaced screens, liquid-crystal screens, and the use of two closely spaced screens in slow relative orbital motion. We describe a simplified, two-screen support that permits only linear screen motion, and show that such motion provides total speckle elimination. An analysis of speckle in such screens is presented which accounts for the observed remarkable sensitivity of the speckle pattern to minute screen displacements. To confirm this analysis we have measured the speckle pattern’s correlation as a function of screen displacement using the speckle interferometry method of Francon. We consider the effects of a spatially and spectrally extended incandescent light source, and conclude that these effects are negligible in our application compared to the effect of screen motion. We show that these three speckle-reducing effects (screen motion, spatial extent of the source, and spectral extent of the source) can be considered together by introducing the notion of space-time correlation cells.