Showing papers on "Impulse noise published in 2004"

A Variational Approach to Remove Outliers and Impulse Noise

Abstract: We consider signal and image restoration using convex cost-functions composed of a non-smooth data-fidelity term and a smooth regularization term. We provide a convergent method to minimize such cost-functions. In order to restore data corrupted with outliers and impulsive noise, we focus on cost-functions composed of an e1 data-fidelity term and an edge-preserving regularization term. The analysis of the minimizers of these cost-functions provides a natural justification of the method. It is shown that, because of the e1 data-fidelity, these minimizers involve an implicit detection of outliers. Uncorrupted (regular) data entries are fitted exactly while outliers are replaced by estimates determined by the regularization term, independently of the exact value of the outliers. The resultant method is accurate and stable, as demonstrated by the experiments. A crucial advantage over alternative filtering methods is the possibility to convey adequate priors about the restored signals and images, such as the presence of edges. Our variational method furnishes a new framework for the processing of data corrupted with outliers and different kinds of impulse noise.

Advanced impulse Detection Based on pixel-wise MAD

Abstract: A new method for impulse noise removal is presented, where a robust estimator of the variance, MAD (median of the absolute deviations from the median), is modified and used to efficiently separate noisy pixels from the image details. The algorithm is free of varying parameters, requires no previous training or optimization, and successfully removes all types of impulse noise. The pixel-wise MAD concept is straightforward, low in complexity, and achieves high filtering performance.

An iterative procedure for removing random-valued impulse noise

Abstract: This work proposes a two-stage iterative method for removing random-valued impulse noise. In the first phase, we use the adaptive center-weighted median filter to identify pixels which are likely to be corrupted by noise (noise candidates). In the second phase, these noise candidates are restored using a detail-preserving regularization method which allows edges and noise-free pixels to be preserved. These two phases are applied alternatively. Simulation results indicate that the proposed method is significantly better than those using just nonlinear filters or regularization only.

A recursive least M-estimate algorithm for robust adaptive filtering in impulsive noise: fast algorithm and convergence performance analysis

Abstract: This paper studies the problem of robust adaptive filtering in impulsive noise environment using a recursive least M-estimate algorithm (RLM). The RLM algorithm minimizes a robust M-estimator-based cost function instead of the conventional mean square error function (MSE). Previous work has showed that the RLM algorithm offers improved robustness to impulses over conventional recursive least squares (RLS) algorithm. In this paper, the mean and mean square convergence behaviors of the RLM algorithm under the contaminated Gaussian impulsive noise model is analyzed. A lattice structure-based fast RLM algorithm, called the Huber Prior Error Feedback-Least Squares Lattice (H-PEF-LSL) algorithm is derived. Part of the H-PEF-LSL algorithm was presented in ICASSP 2001. It has an order O(N) arithmetic complexity, where N is the length of the adaptive filter, and can be viewed as a fast implementation of the RLM algorithm based on the modified Huber M-estimate function and the conventional PEF-LSL adaptive filtering algorithm. Simulation results show that the transversal RLM and the H-PEF-LSL algorithms have better performance than the conventional RLS and other RLS-like robust adaptive algorithms tested when the desired and input signals are corrupted by impulsive noise. Furthermore, the theoretical and simulation results on the convergence behaviors agree very well with each other.

Effective impulse detector based on rank-order criteria

Abstract: A new impulsive noise detection technique is presented here. Preserving edges and details in the process of impulsive noise filtering is an important problem. To avoid image smoothing, only corrupted pixels must be filtered. In order to identify the corrupted pixels, a new impulse detector is proposed. This detector is based on a comparison of signal samples within a narrow rank window by both rank and absolute value. It is efficient, very fast, and can be used with any filter (even iteratively), without smoothing an image.

Turbo decoding in impulsive noise environment

Abstract: Power line channels often suffer from impulsive interference generated by electrical appliances. Therefore, power line communication (PLC) degrades due to such impulsive interference. Middleton's class A noise model is frequently utilized for the modeling of such impulsive noise environments. We deal with turbo decoding for turbo codes over an additive white class A noise (AWAN) channel. We propose a turbo decoding which is suitable for AWAN channels. In addition, we show the BER (bit error rate) performance of the proposed turbo decoding in a class A noise environment by computer simulation.

A simple neuro-fuzzy impulse detector for efficient blur reduction of impulse noise removal operators for digital images

Abstract: A new impulse noise detector based on neuro-fuzzy methods is presented. The proposed detector comprises two identical neuro-fuzzy subdetectors combined with a decision maker. The internal parameters of the subdetectors are adaptively adjusted by training. Training of the subdetectors is accomplished by using a simple computer generated artificial image. The detector can be combined with any impulse noise removal operator. The operation of the detector is completely independent of the noise removal operator and it has no influence on the filtering behavior of the operator. Experimental results show that the proposed detector significantly reduces the distortion effects of any impulse noise removal operator even if the operator already has its own noise detector.

Impulse rejection filter for artifact removal in spectral analysis of biomedical signals

Abstract: Biomedical signals are frequently corrupted with artifact that occurs rarely, but is impulsive and large amplitude when it does occur. Because the artifact spans a broad frequency range that overlaps with the signal spectrum, linear filters cannot remove it. Because it is large in amplitude, it dominates characterizations of the signals based on second-order statistics such as correlation and spectral analysis. In this study we assess the ability of impulse rejection filters to remove the effect of synthetic PVCs in interbeat interval series from patients with a normal sinus rhythm. The simulation results demonstrate that the PVCs severely corrupt the estimated heart rate power spectral density (PSD), impulse rejection filters are effective at removing this effect, and the filter performance is robust to the choice of user-specified parameters.

Adaptive fuzzy switching filter for images corrupted by impulse noise

Abstract: An adaptive fuzzy switching filter is presented that adopts a fuzzy logic approach for the enhancement of images corrupted by impulse noise. In order to achieve optimal detail preservation, we develop the maximum-minimum exclusive median method to estimate the current pixel. Simulation results indicate that the proposed filter impressively outperforms other techniques in terms of noise suppression and detail preservation across a wide range of impulse noise corruption, ranging from 1% to 90%.

Adaptive Two-Pass Median Filter Based on Support Vector Machines for Image Restoration

Abstract: In this letter, a novel adaptive filter, the adaptive two-pass median (ATM) filter based on support vector machines (SVMs), is proposed to preserve more image details while effectively suppressing impulse noise for image restoration. The proposed filter is composed of a noise decision maker and two-pass median filters. Our new approach basically uses an SVM impulse detector to judge whether the input pixel is noise. If a pixel is detected as a corrupted pixel, the noise-free reduction median filter will be triggered to replace it. Otherwise, it remains unchanged. Then, to improve the quality of the restored image, a decision impulse filter is put to work in the second-pass filtering procedure. As for the noise suppressing both fixed-valued and random-valued impulses without degrading the quality of the fine details, the results of our extensive experiments demonstrate that the proposed filter outperforms earlier median-based filters in the literature. Our new filter also provides excellent robustness at various percentages of impulse noise.

Classifier-augmented median filters for image restoration

Abstract: Developed in this paper is a new approach that augments a fuzzy classifier to determine whether or not the operating pixel, centered in the sliding window, should be involved with the impulse noise filtering process. Owing to the inclusion of the fuzzy K-nearest neighbor (K-NN) scheme, any central operating pixel that is not noise corrupted can be effectively detected and then left unchanged. Thus, the unnecessary pixel replacement can be avoided and the details and signal structure of the image will be best retained. If the center point is found to be noise corrupted, the proposed classifier-augmented median filter facilitates the filtering action only on a subset of pixels, which are not noise contaminated in the window. Due to this impulse pixel exclusion, the biased estimation caused from impulses can be eliminated and, thus, obtains a better estimation of the center pixel. Experimental results showed that this new approach largely outperformed several existing schemes for image noise removal.

Reduced-delay protection of DSL systems against nonstationary disturbances

Abstract: In addition to being designed to successfully cope with stationary noise, crosstalk, and intersymbol interference, digital subscriber loop (DSL) systems need to be shielded from nonstationary disturbances, such as impulse noise and RF interference. Currently, deployed DSL systems achieve protection against nonstationary interference using a combination of Reed-Solomon (RS) codes and interleaving. However, interleaving results in delay. Long delays are undesirable in high-rate systems that support interactive applications. In this study, it is shown that the interleaving delay of DSL systems can be significantly reduced by performing erasure decoding of the RS codewords at the receiver. Three different techniques for determining the erasures are proposed. Use of the techniques results in a reduction of the interleaving delay that is required to mitigate worst-case impulse noise by up to a factor of 2, which is verified by simulation. Moreover, the techniques do not require any changes at the transmitter and therefore guarantee compatibility with currently deployed systems.

Noise bucket effect for impulse noise in OFDM

Abstract: Impulse noise is a significant problem in some orthogonal frequency division multiplexing (OFDM) applications. It has been observed in practice that the degradation caused by impulse noise depends only on the total energy of the noise during each OFDM symbol, not on the structure of the noise. This ‘noise bucket’ effect is explained by showing that even for a small number of impulses per symbol the noise distribution at the input of the receiver decision device is close to Gaussian. This is because of the spreading effect of the discrete Fourier transform.

Impulse noise mitigation for OFDM using decision directed noise estimation

Abstract: The paper describes a new technique for mitigating the effects of impulse noise in OFDM. An estimate is made of the noise component in each received input sample. The estimates are based on the transmitted data. No pilot tones are required. When the estimate is large enough to indicate that impulse noise is present in the sample, the estimated noise component is subtracted from the input sample before final demodulation. Estimates of the noise are obtained from preliminary decisions based on the noisy signal. The technique is effective because the energy from each noise impulse is spread across the received spectrum. The technique can also be applied to multicarrier CDMA. Simulations show that, in cases of practical importance, the symbol error rate can be reduced by several orders of magnitude.

Detail-preserving restoration of impulse noise corrupted images by a switching median filter guided by a simple neuro-fuzzy network

Abstract: A new operator for the restoration of digital images corrupted by impulse noise is presented. The proposed operator is a simple recursive switching median filter guided by a neuro-fuzzy network functioning as an impulse detector. The internal parameters of the neuro-fuzzy impulse detector are adaptively optimized by training. The training is easily accomplished by using simple artificial images that can be generated in a computer. The most distinctive feature of the proposed operator over other operators is that it offers excellent detail- and texture-preservation performance, while effectively removing noise from the input image. Extensive experiments show that the proposed operator may be used for effcient restoration of digital images corrupted by impulse noise without distorting the useful information in the image.

Temporary changes in hearing after exposure to shooting noise.

Abstract: Objectives: Firearm is a common source of impulse noise that may potentially damage hearing organ. It has been suggested that otoacoustic emissions, particularly transient-evoked otoacoustic emissions (TEOAE), might be more sensitive than pure-tone audiometry (PTA) in the assessment of changes to cochlea caused by noise. The aim of this study was to: (i) evaluate exposure to impulse noise from small-caliber weapons, (ii) compare the post-exposure changes in hearing measured by PTA and TEOAE and correlate them with noise parameters. Materials and Methods: The study included 18 male hunters (group I) and 28 candidate policemen (group II) exposed to impulse noise from small firearms during target practices. Group I was unprotected during shooting, whereas group II used commonly available hearing protectors. PTA and TEOAE were performed before and 2-10 min after shooting. Exposure to impulse noise was evaluated by in situ measurements. Results: Groups I and II were exposed to 3-4 and 4-144 impulses of noise at mean C-weighted peak sound pressure levels of 154 dB and 156 dB, respectively. No post-exposure audiometric threshold shift was observed in group I. Significant reductions of TEOAE levels were found both for the whole response (-2.2 dB SPL) and for 1/2 -octave band responses in the frequency range of 1000-4000 Hz (from -1.6 to -3.0 dB SPL). These changes were not correlated with C- weighted peak sound pressure levels or equivalent-continuous A-weighted sound pressure level. Significant correlation was found for peak sound pressure and maximum sound pressure levels in 1/3-octave bands in the frequency range corresponding with the main part of the acoustic energy of impulses (correlation coefficients r from -0.58 to -0.77, p < 0.05). In group II neither PTA nor TEOAE showed significant hearing impairment after shooting. Conclusions: The results show that even short-term exposure to impulse noise from small-calibre firearms might cause temporary hearing impairment measured by TEOAE. Therefore, the use of earmuffs is strongly recommended, because most of them seem to effectively attenuate impulse noise from small-calibre firearms.

Adaptive communication systems and methods

Abstract: Methods and communication systems are presented, in which impulse noise is monitored on a communication channel, and impulse noise protection parameters are adjusted according to the monitored impulse noise without interrupting communication service.

A Simple Neuro-Fuzzy Edge Detector for Digital Images Corrupted by Impulse Noise

Abstract: A new neuro-fuzzy edge detector for digital images corrupted by impulse noise is presented. The structure of the detector is very simple and comprises four identical neuro-fuzzy subdetectors and a postprocessor. The internal parameters of the detector are determined by training. The detector efficiently extracts edges in digital images corrupted by impulse noise without requiring the filtering of the noise.

Real-time adaptive image impulse noise suppression

Abstract: In this paper, a new intelligent hardware module suitable for the computation of an adaptive median filter is presented for the first time. The function of the proposed circuit is to detect the existence of impulse noise in an image neighborhood and apply the operator of the median filter only when it is necessary. The noise detection procedure can be controlled so that a range of pixel values is considered as impulse noise. In this way, the blurring of the image in process is avoided, and the integrity of edge and detail information is preserved. Experimental results with real images demonstrate the improved performance. The proposed digital hardware structure is capable to process gray-scale images of 8-bit resolution and is fully pipelined, whereas parallel processing is used in order to minimize computational time. In the presented design, a 3/spl times/3 or 5/spl times/5 pixel image neighborhood can be selected for the computation of the filter output. However, the system can be easily expanded to accommodate windows of larger sizes. The proposed digital structure was designed, compiled and simulated using the MAX+PLUS II Programmable Logic Development System by Altera Corporation. For the implementation of the system the EPF10K200SRC240-1 field-programmable gate array device of the FLEX10KE device family is utilized, and it can be used in industrial imaging applications where fast processing is required. The typical clock frequency is 65 MHz.

Radiometric measurement of Circuit Breaker interpole switching times

Abstract: Monitoring the switching times of circuit breakers is important in the condition assessment of the operating mechanism. Although methods exist for this, they are not applicable to existing plant without retrofitting. Recent research shows that arcing produces impulsive radio-frequency radiation. Using direct digital sampling of the antenna signals, impulses from operating circuit breakers (CBs) may be recorded. From timing analysis of the received impulses, the interpole switching time of the CB can be measured. Results of this method are shown for a field trial on a 132-kV SF/sub 6/ CB attached to a capacitor bank. The relationship between the opening and closing impulses is discussed. This method of timing measurement can be applied to an energized CB. Measurement of the interpole switching times is completely noninvasive, whereas the overall switching time requires a clamp CT fitted on the CB wiring.

Urban wide-band measurement of the UMTS electromagnetic environment

Abstract: Measurements of impulsive noise in the universal mobile telecommunications system (UMTS) electromagnetic environment in urban areas have been conducted and its effect on the UMTS system is analyzed. An impulsive noise-measurement system for the UMTS frequency band has been designed and built, which meets and improves the main features of classical equipments used to measure noise, offering inphase and quadrature outputs simultaneously. This measurement system was carefully calibrated before a measurement campaign was conducted in an urban environment to get impulsive noise statistics. Results show that noise pulses may have high power, long duration, and high repetition rate, so the performance of UMTS could be significantly reduced.

Methods and apparatuses for detecting impulse noise in a multi-carrier communication system

Abstract: Embodiments of an apparatus, system, and method are described for a multi-carrier communication system that detects for impulse noise present on a transmission medium. Values of peak error samples may be measured to determine an approximate magnitude of the average peak error samples present on a transmission medium. An average error value of all of the error samples may be measured to determine a standard deviation of a Gaussian distribution of background noise. An amount of peak error samples may be compared to a threshold value that is based upon a standard deviation derived from the background noise to determine if impulse noise is present on a particular tone.

Landsat-7 ETM+ on-orbit reflective-band radiometric characterization

Abstract: The Landsat-7 Enhanced Thematic Mapper Plus (ETM+) has been and continues to be radiometrically characterized using the Image Assessment System (IAS), a component of the Landsat-7 Ground System Key radiometric properties analyzed include: overall, coherent, and impulse noise; bias stability; relative gain stability; and other artifacts The overall instrument noise is characterized across the dynamic range of the instrument during solar diffuser deployments Less than 1% per year increases are observed in signal-independent (dark) noise levels, while signal-dependent noise is stable with time Several coherent noise sources exist in ETM+ data with scene-averaged magnitudes of up to 04 DN, and a noise component at 20 kHz whose magnitude varies across the scan and peaks at the image edges Bit-flip noise does not exist on the ETM+ However, impulse noise due to charged particle hits on the detector array has been discovered The instrument bias is measured every scan line using a shutter Most bands show less than 01 DN variations in bias across the instrument lifetime The panchromatic band is the exception, where the variation approaches 2 DN and is related primarily to temperature The relative gains of the detectors, ie, each detector's gain relative to the band average gain, have been stable to /spl plusmn/01% over the mission life Two exceptions to this stability include band 2 detector 2, which dropped about 1% in gain about 35 years after launch and stabilized, and band 7 detector 5, which has changed several tenths of a percent several times since launch Memory effect and scan-correlated shift, a hysteresis and a random change in bias between multiple states, respectively, both of which have been observed in previous Thematic Mapper sensors, have not been convincingly found in ETM+ data Two artifacts, detector ringing and "oversaturation", affect a small amount of ETM+ data

Decision directed impulse noise mitigation for OFDM in frequency selective fading channels [DVB-T example]

Abstract: Impulse noise is a significant problem in some OFDM applications, including digital television broadcasting. In this paper, we study a novel decision directed impulse mitigation algorithm, both analytically and with simulations for the DVB-T parameters. In this algorithm, the noise component in each received input sample is estimated based on preliminary decisions on the transmitted data. When the estimate is large enough to indicate that impulse noise is present in the sample, the estimated noise component is subtracted from the input sample before final demodulation. This technique has been shown to be extremely effective in flat fading channels. In this paper, its application in frequency selective fading channels is analyzed. The optimum weighting factors for combining noise estimates from subcarriers subject to different fading are calculated. Simulation results are presented for Rayleigh and Ricean channels which show that the technique can reduce the error rates due to impulsive noise by an order of magnitude.

Impulse noise reduction to an MCM signal

Abstract: A method reduces noise in a multiple carrier modulated (MCM) signal. Such a method may include: estimating impulse noise based in the equalized signal; and removing a portion of the noise in the equalized signal as a function of the estimated impulse noise. An apparatus reduces noise in the MCM. Such an apparatus may include: a down-converter; an analog to digital converter to digitize the output of the down-converter; a guard-interval removing unit operable upon the digitized output of the down-converter; and a combined FFT, equalization and impulse-noise-compensation unit operable upon a signal from the guard-interval-removing unit.

System for monitoring exposure to impulse noise

Abstract: In one embodiment, a system for monitoring exposure to impulse noise includes a sound-sensing device, such as a microphone or other type of pressure transducer, operable to sense impulse noise, and a storage module operable to store the waveform of the impulse noise sensed by the sound-sensing device. The sound-sensing device desirably is operable to sense impulses that are greater than 146 dB, such as impulses created by construction machinery and firearms. The system also can include a processor operable to calculate one or more noise parameters of the impulse noise from the waveform, and a user interface program operable to display said one or more noise parameters selected by a user.

Using an exact radial basis function artificial neural network for impulsive noise suppression from highly distorted image databases

Abstract: In this paper, a new filter, RM, which is based on exact radial basis function artificial neural networks, is proposed for the impulsive noise suppression from highly distorted images. The RM uses Chi-Squared based goodness-of-fit test in order to find corrupted pixels more accurately.The proposed filter shows a high performance at the restoration of images distorted by impulsive noise. The extensive simulation results show that the proposed filter achieves a superior performance to the other filters mentioned in this paper in the cases of being effective in noise suppression and detail preservation, especially when the noise density is very high.