Showing papers on "Noise reduction published in 1988"

A transformation for ordering multispectral data in terms of image quality with implications for noise removal

Abstract: A transformation known as the maximum noise fraction (MNF) transformation, which always produces new components ordered by image quality, is presented. It can be shown that this transformation is equivalent to principal components transformations when the noise variance is the same in all bands and that it reduces to a multiple linear regression when noise is in one band only. Noise can be effectively removed from multispectral data by transforming to the MNF space, smoothing or rejecting the most noisy components, and then retransforming to the original space. In this way, more intense smoothing can be applied to the MNF components with high noise and low signal content than could be applied to each band of the original data. The MNF transformation requires knowledge of both the signal and noise covariance matrices. Except when the noise is in one band only, the noise covariance matrix needs to be estimated. One procedure for doing this is discussed and examples of cleaned images are presented. >

A microphone array with adaptive post-filtering for noise reduction in reverberant rooms

Abstract: The author presents a self-adapting noise reduction system which is based on a four-microphone array combined with an adaptive postfiltering scheme. Noise reduction is achieved by utilizing the directivity gain of the array and by reducing the residual noise through postfiltering of the received microphone signals. The postfiltering scheme depends on a Wiener filter estimating the desired speech signal and is computed from short-term measurements of the autocorrelation and cross-correlation functions of the microphone signals. The noise reduction system has been tested experimentally in a typical office room. The system produces an enhanced speech signal with barely noticeable residual noise if the input SNR is greater than 0 dB. The received noise power-measured in the absence of the speech signal-can be reduced by 28 dB. >

The two-dimensional adaptive LMS (TDLMS) algorithm

Abstract: A two-dimensional least-mean-square (TDLMS) adaptive algorithm based on the method of steepest decent is proposed and applied to noise reduction in images. The adaptive property of the TDLMS algorithm enables the filter to have an improved tracking performance in nonstationary images. The results presented show that the TDLMS algorithm can be used successfully to reduce noise in images. The algorithm complexity is 2(N*N) multiplications and the same number of additions per image sample, where N is the parameter-matrix dimension. Analysis and convergence properties of the LMS algorithm in the one-dimensional case presented by other authors is shown to be applicable to this algorithm. The algorithm can be used in a number of two-dimensional applications such as image enhancement and image data processing. >

An algorithm for noise suppression in dual energy CT material density images

Abstract: Dual-energy material density images obtained by prereconstruction-basis material decomposition techniques offer specific tissue information, but they exhibit relatively high pixel noise. It is shown that noise in the material density images is negatively correlated and that this can be exploited for noise reduction in the two-basis material density images. The algorithm minimizes noise-related differences between pixels and their local mean values, with the constraint that monoenergetic CT values, which can be calculated from the density images, remain unchanged. Applied to the material density images, a noise reduction by factors of 2 to 5 is achieved. While quantitative results for regions of interest remain unchanged, edge effects can occur in the processed images. To suppress these, locally adaptive algorithms are presented and discussed. Results are documented by both phantom measurements and clinical examples. >

Observation of 4.2-K equilibrium-noise squeezing via a Josephson-parametric amplifier.

Abstract: We have demonstrated 42% squeezing of 4.2-K thermal noise using a Josephson-parametric amplifier operated at 19.4 GHz. The amplifier has been operated at 0.1 K with an excess noise of 0.28 K referred to the input port. This is less than the vacuum fluctuation noise h\ensuremath{ u}/2k=0.47 K at 19.4 GHz. The amplifier thus is less noise than a linear phase-insensitive amplifier such as a maser could in principle be.

Diagnosis and reduction of conducted noise emissions

Abstract: A systematic method for the diagnosis and reduction of conducted noise emissions is described. The method consists of a device for determining whether the differential- or common-mode component of conducted noise is dominant along with a simplified equivalent circuit of the power supply filter for each component. The procedure consists of first using the device to determine which noise-component is dominant in a particular frequency range and then using the simplified equivalent circuits to determine whether an anticipated change in value of an element in the power supply filter will be effective. >

Noise reduction using connectionist models

Abstract: Using a back propagation network learning algorithm, a four-layered feed-forward network is trained on learning samples to realize a mapping from the set of noisy signals a set of noise-free signals. Computer experiments were carried out on 12 kHz sampled Japanese speech data, using stationary and nonstationary noise. The experiments showed that the network can indeed learn to perform noise reduction. Even for noisy speech signals that had not been part of the training data, the network successfully produced noise-suppressed output signals. >

Noise reduction in dynamical systems

Abstract: A method is described for reducing noise levels in certain experimental time series. An attractor is reconstructed from the data using the time-delay embedding method. The method produces a new, slightly altered time series which is more consistent with the dynamics on the corresponding phase-space attractor. Numerical experiments with the two-dimensional Ikeda laser map and power spectra from weakly turbulent Couette-Taylor flow suggest that the method can reduce noise levels up to a factor of 10.

Method for enhancing image data by noise reduction or sharpening

Abstract: An image enhancing process promotes either noise reduction or image sharpening on a pixel-by-pixel basis as a function of the recognition of specific patterns of sampled pixel values surrounding each pixel to be enhanced The sampled pixel values are divided into two or more subgroups and the enhanced pixel value is provided to promote either image sharpening or noise reduction as a function of the number of pixel values in the different subgroups and their positions relative to each other in the subgroups

A 13 bit ISDN-band oversampled ADC using two-stage third order noise shaping

Abstract: A 13-bit 80-kHz baseband analog-to-digital converter suitable for use in applications such as the ISDN U-interface is described. Two-stage third-order noise shaping permits the use of asampling frequency of only 2.56 MHz. The circuit has been implemented using conventional single-ended switched-capacitor techniques in a 1.5- mu m CMOS process. >

Noise reduction system

Abstract: In order to overcome problems in an active noise reduction system of sound buffets at low frequency and signal enhancement caused by imperfect transfer functions of a noise cancelling sound generator and a microphone, one or more high pass filters for reducing low frequency signals are provided in a feedback loop between the sound generator and microphone. A low pass filter is provided for extending the bandwidth of the system but which does not introduce unduly large phase shifts.

Improving TV picture quality with linear-median type operations

Abstract: The FMH filter concept for video signal processing which combines the features of linear and median filters is introduced. In FMH (FIR median hybrid) filters, the overall output is the median calculated over the outputs of FIR subfilters, and the central input sample, the number of values to be sorted, is independent of the filter size; only the size of the FIR subfilters is altered. The noise reduction properties of FMH filters are similar to those of median filters. Applications within the field of digital enhanced TV, EDTV, and HDTV are presented with emphasis on noise suppression and image coding. >

Enhancement of chest radiographs with gradient operators

Abstract: Reference is made to the Sobel and Roberts gradient operators used to enhance image edges. Overall, the Sobel operator was found to be superior to the Roberts operator in edge enhancement. A theoretical explanation for the superior performance of the Sobel operator was developed based on the concept of analyzing the x and y Sobel masks as linear filters. By applying pill-box, Gaussian, or median filtering prior to applying a gradient operator, noise was reduced. The pill-box and Gaussian filters were more computationally efficient than the median filter with approximately equal effectiveness in noise reduction. >

Noise reduction technique for scanning tunneling microscopy

Abstract: Noise stemming from mechanical vibration, electronic noise, or low frequency (1/f power spectrum) inherent in the tunneling process, often limits the resolution, speed, or range of application of scanning tunneling microscopy (STM). We demonstrate a technique for minimizing the effect of these noise sources on the STM image. In our method, the tunneling tip is vibrated parallel to the sample surface at a frequency f0, above that of the feedback response frequency. Two signals are obtained simultaneously: the conventional topography, and a differential image corresponding to the amplitude of current modulation at f0. The resultant ac signal can be simply related to the normal STM topographic image, with significant improvement in the signal‐to‐noise ratio.

Low noise - low power monolithic multiplexing readout electronics for silicon strip detectors

Abstract: A 128 channel readout chip suitable for readout with 50 μm pitch has been developed in CMOS technology It provides signal amplification, parallel data storage and serial readout Switched capacitor technique is used for noise reduction by multicorrelated sampling and simultaneously for second stage amplification Power consumption is controlled by an externally applied reference voltage thereby allowing for an optimization of speed and noise versus power consumption for the individual needs of the particular experiment Pulsed mode operation for further reduction of heat dissipation is easily possible without cutting the supply voltages Very good noise performance (250+45 C D [pF] electrons) low input impedance ( C eff > 200 pF) and large amplification (70 mV/fC) have been obtained at very low power consumption (16 mW per channel) The chip may be used for both synchronous (eg collider) and asynchronous (fixed target) applications where the time of the event is not known in advance A second version with only 64 channels suitable for 100 μm pitch is in preparation Further developments presently under way include the introduction of combinded CMOS-JFET technology

Local noise prediction filtering for central induction transient electromagnetic sounding

Abstract: Local noise prediction filtering (LNPF) is a method of noise reduction designed for use with the in‐loop transient electromagnetic (TEM) method of exploration. LNPF is based on simultaneous measurements of three orthogonal magnetic‐field components and the calculation of a time‐domain filter which predicts the vertical component from the two horizontal components. For in‐loop, or central induction, sounding over a horizontally layered earth, the TEM signal is contained wholly within the vertical component. Thus the predicted time series obtained with LNPF is the predicted electromagnetic noise which can be subtracted from the measured vertical component in subsequent processing. For low‐frequency noise, the method results in improvements in the signal‐to‐noise ratio of about a factor of five using a three‐point prediction filter. Longer filters give superior performance but are computationally intensive. The depth of exploration should increase by 40 percent, due to the five‐fold increase in signal‐to‐noi...

Radar video detector and target tracker

Abstract: A system for detecting and tracking a multiplicity of targets averages radar video returns over small sectors for data smoothing and noise reduction, provides adaptive thresholding by determining noise levels in an area of interest and establishes a detection threshold in accordance with such noise level, stores the video data for reach target of interest so that multiple targets on the same bearing may be tracked, and reduces the probability of target swapping by adjusting the target window in accordance with target size and weighting the cells within the window.

Digital image processing for noise reduction in medical ultrasonics

Abstract: The purpose of this project was to investigate the application of digital image processing techniques as a means of reducing noise in medical ultrasonic imaging. Ultrasonic images suffer primarily from a type of acoustic noise, known as speckle, which is generally regarded as a major source of image quality degradation. The origin of speckle, its statistical properties as well as methods suggested to eliminate this artifact were reviewed. A simple model which can characterize the statistics of speckle on displays was also developed. A large number of digital noise reduction techniques was investigated. These include frame averaging techniques performed by commercially available devices and spatial filters implemented in software. Among the latter, some filters have been proposed in the scientific literature for ultrasonic, laser and microwave speckle or general noise suppression and the rest are original, developed specifically to suppress ultrasonic speckle. Particular emphasis was placed on adaptive techniques which adjust the processing performed at each point according to the local image content. In this way, they manage to suppress speckle with negligible loss of genuine image detail. Apart from preserving the diagnostically significant features of a scan another requirement a technique must satisfy before it is accepted in routine clinical practice is real-time operation. A spatial filter capable of satisfying both these requirements was designed and built in hardware using low-cost and readily available components. The possibility of incorporating all the necessary filter circuitry into a single VLSI chip was also investigated. In order to establish the effectiveness and usefulness of speckle suppression, a representative sample from the techniques examined here was applied to a large number of abdominal scans and their effect on image quality was evaluated. Finally, further improvements and possible uses of speckle suppression techniques in other fields were also considered.

Noise cancellation in digitizing system and method

Abstract: A digitizing system includes a differential noise reduction technique wherein spaced parallel grid conductors in a tablet are differentially sensed in order to cancel out locally induced noise signals. Grid conductors also are sensed in a single ended fashion to initially locate a grid conductor conducting a larger induced carrier signal amplitude than any other grid conductor and produce amplitude data that is used to eliminate ambiguities arising from differential sensing of pairs of spaced grid conductors.

Wigner Distribution Function: Relation to Short-Term Spectral Estimation, Smoothing, and Performance in Noise.

Abstract: : The properties and behavior of the Wigner Distribution Function (WDF) are investigated both analytically and by means of a number of simple informative examples. The lack of local temporal averaging when obtaining the instantaneous correlation function, and the lack of weighting the longer delay values when transforming to the instantaneous spectrum, are shown to be the causes of the deleterious interference effects that are inherent to the WDF. The equivalence of short-term spectral estimation to the smoothed WDF offers an attractive alternative with guaranteed positive distribution values and no interference effects. The performance of a processor which estimates the WDF of a signal waveform in the presence of additive noise is investigated in terms of the output mean, bias, and variance. Dependence on filtering the input and time-weighting is allowed and included in the analysis. Numerical application to a particular example is carried out. Keywords: Wigner distribution function; Short term spectral estimation; Smoothing; Noise performance; Linear frequency; Modulation; Interference effects; Gaussian amplitude modulation; Marginals; Moments; Spread of distribution; Positive distributions; Ambiguity function.

An adaptive filter for noise cancelling

Abstract: The author introduces a nonlinear filter for adaptive noise cancelling. The derivation and convergence properties of the filter are presented. The performance, as measured by the signal-to-noise ratio between the signal and its estimate, is compared to that of the commonly used least-mean-square (LMS) algorithm. It is shown, through simulation, that the proposed canceller has, on the average, better performance than the LMS canceller. It is based on the Pontryagin minimum principle and the method of invariant imbedding, and its computational time is about 10% that of the LMS in the cases studied, which is a substantial improvement. >

Quantum noise reduction via maser memory effects: Theory and applications.

Abstract: In many high-precison laser measurements spontaneous-emission quantum noise determines the ultimate sensitivity. We demonstrate here that when the experimental circumstances restrict us to short measurement times, the spontaneous-emission noise can be substantially reduced by the utilization of long-lived atoms as the masing medium.

Multichannel active sound control using adaptive filtering

Abstract: The active control of harmonic sound using multiple secondary sources and multiple error microphones is formulated in an adaptive digital filtering framework. A stochastic gradient algorithm is presented to minimize the sum of the squares of the error microphone outputs by adapting the coefficients of an array of FIR (finite-impulse response) filters driving the secondary sources. The properties and implementation of the algorithm are discussed and some results are presented which demonstrate that the noise at the engine firing frequency inside an automobile can be reduced by 10-15 dB using a practical implementation of such an active sound control system, which had a response time of 0.1 s in this application. >

Si Bipolar 2gs/s 6b Flash A/d Conversion Lsi

Abstract: A 2GHz SAMPLING-RATE monolithic 6 b A/D converter with a 1.7GHz input bandwidth and more bits than 4.7 up t o Nyquist frequency at a lGHz sampling rate will be described. Advanced bipolar technology, and dynamic accuracy enhancement techniques, such as a quasi-Gray encoder contributed t o the design’ ’ . A simplified block diagram of the LSI is shown in Figure 1. An emitter follower type buffer amplifier, installed on the same chip, provides a wide input bandwidth, to reduce harmonic distortion due t o nonlinear input capacitance of the comparator array and to suppress a kickback noise increase due t o parasitic inductance in the off-chip buffer amplifier assembly. The comparator circuit has latched comparator with a preamplifier whose power supply lines are separated from those of the latched comparator t o suppress kickback noise’. An encoder was optimized for 6b organization t o minimize glitch noise. Dual-input-NOR gates were used in the encoder. Speed and power related factors are shown in Figure 2, where the power dependence of the comparator response time and the basic ECL gate delay time is illustrated. Response time reaches its minimum value and does not decrease in spite of increased power. A high-speed response time of 130ps was attained by setting comparator circuit power dissipation near minimum response time. The comparator circuit consists of two stages and operates at a overdrive voltage of 16mV. Response time was 3.8 times as long as the minimum gate delay time of 34ps. The bias current of each emitter-follower stage was designed to be about half that of the following differential stage, t o prevent speed limitation caused by the output impedance of each emitter follower stage. The minimum preamplifier gain, which guarantees dc linearity, was obtained from a statistical analysis of comparator offset voltage. Circuit simulation provided the optimum (constant) power allocation between preamplifier and latched comparator.

Noise reduction circuit

Abstract: A noise reduction circuit in which a video signal (SI) is divided into a first signal (SL) having low frequency component and a second signal (SH1) having high frequency component, the above second signal (SH1) is divided into a third signal (SH2) having an amplitude more than a predetermined value and a fourth signal (SH3) having an amplitute less than the predetermined value, a noise reduction process using a delay circuit (12) is applied to the above fourth signal (SH3) to obtain a fifth signal (SH4), and the above first signal (SL), third signal (SH2) and fifth signal (SH4) are added, the noise reduction circuit being applicable to apply to a television receiver, etc.

On the Rice model of noise in FM receivers

Abstract: The so-called click-and-Gaussian-noise model for the output of a limiter-discriminator receiver for frequency-modulated signals, first proposed by S.O. Rice in 1963, is reviewed. A short survey is presented of the subsequent research that it generated and of some practical applications that it motivated. A more detailed analysis of parameters encountered in the Rice model is carried out with emphasis on their pertinence to click detection. These results are applied to the understanding of the limitations and to the interpretation of the performance of several noise threshold extension techniques for analog modulations and of error reduction techniques for digital modulations that depend on click detection and elimination. >

Noise reduction circuit for video signal having field memory

Abstract: A noise reduction circuit allows a field memory to store 1-field data of a video signal through a subtracting circuit. The video signal is supplied from a VTR through an A/D converter. The noise reduction circuit causes a subtracting circuit to subtract a delayed video signal, which is supplied from the field memory with a 1-field time delay, from the video signal and allows the resultant signal to be output as a field difference signal. A noise component included in the video signal is extracted by a noise extracting circuit in accordance with the field difference signal, and is output to the subtracting circuit. In a comparing circuit, the noise component is compared with a predetermined reference value so as to determine whether the video signal represents a motion or motionless picture. In accordance with this determination result, memory control circuit controls whether to write the video signal supplied from the subtracting circuit in the field memory. In addition, a video signal from which the noise component is removed is supplied from the subtracting circuit and monitored on a CRT display through a D/A converter or the like.

Vector FIR-median hybrid filters for multispectral signals

Abstract: The concept of a vector median (VM) using linear substructures is introduced for multispectral signals. It is shown that the VM filter utilises the correlation between the spectral components, which is an important property when the edge shape and location should be preserved for each signal component simultaneously. The vector median approach is applied to FIR-median hybrid (FMH) filters. These filters are shown to have good noise attenuation and a low bias error near edges. Vector median filters can be applied, for example, to standard colour images in TV systems and to multispectral satellite images.

High Tc superconducting film as a fast nonlinear switch for noise discrimination in digital circuits

Abstract: Measurements of fast nonlinear switching of a high Tc superconducting thin film at 70 K between the dissipative state (induced by an electrical current) and superconducting state are reported. System rise and fall times are measured to be about 1 ns and are limited by the parasitic components of the electrical circuitry. A novel scheme for noise discrimination in digital circuits using this switching has been proposed and experimentally demonstrated for speeds exceeding 200 Mb/s. This method allows significant reduction of amplitude noise and improvement of signal‐to‐noise ratio in digital circuits.