Showing papers on "Noise reduction published in 1980"

Digital Image Enhancement and Noise Filtering by Use of Local Statistics

Abstract: Computational techniques involving contrast enhancement and noise filtering on two-dimensional image arrays are developed based on their local mean and variance. These algorithms are nonrecursive and do not require the use of any kind of transform. They share the same characteristics in that each pixel is processed independently. Consequently, this approach has an obvious advantage when used in real-time digital image processing applications and where a parallel processor can be used. For both the additive and multiplicative cases, the a priori mean and variance of each pixel is derived from its local mean and variance. Then, the minimum mean-square error estimator in its simplest form is applied to obtain the noise filtering algorithms. For multiplicative noise a statistical optimal linear approximation is made. Experimental results show that such an assumption yields a very effective filtering algorithm. Examples on images containing 256 × 256 pixels are given. Results show that in most cases the techniques developed in this paper are readily adaptable to real-time image processing.

An Analysis of a Real-Time Transform Domain Filtering Digital Communication System--Part I: Narrow-Band Interference Rejection

Abstract: This paper provides a detailed analysis of the performance of systems recently proposed by various authors in which the received signal is Fourier transformed in real time (usually with a surface acoustic wave device) and then filtered by a multiplication of the transformed signal by an appropriate transfer function. We shall refer to this operation as transform domain filtering. General expressions for the output waveforms of the system will be derived, and a specific example illustrating the performance of the system when operating in the presence of a narrow-band interferer plus additive white Gaussian noise will be presented. It will be shown that certain filtering techniques not feasible in conventional systems, such as filtering with ideal bandpass filters, become straightforward using transform domain filtering. Finally, a receiver will be described which will eliminate that intersymbol interference between adjacent data symbols due to filtering at the receiver.

Influence of Propeller Design Parameters on Far-Field Harmonic Noise in Forward Flight

Abstract: A theory for harmonic noise radiation is studied for general guidance to the designer and is applied to some propeller noise problems of current interest. Only the linear sources are studied in detail. The frequency domain results clarify the role of acoustic noncompactness (noise cancellation due to finite chord and span effects). Nondimensional parameters arising from the analysis give design guidance by showing the potential for noise reduction due to changes in airfoil section and blade sweep, twist, and taper as functions of operating conditions. Conventional propellers are shown to be relatively insensitive to variations in blade design. However, advanced turbopropellers (prop fans) currently under development are decidedly noncompact because of their high solidity and speed. Examples of chord wise and span wise cancellation are given illustrating substantial benefits of sweep.

Foliage as a low‐pass filter: Experiments with model forests in an anechoic chamber.

Abstract: In order to investigate the influence of foliage on sound transmission through vegetation, we have examined four model forest situations in an anechoic chamber In general, we found that the foliage acts in the midfrequencies as a noise amplifier, which is important for the vocalization and communication of animals In the high frequencies the foliage of plants acts as a good noise filter The acoustic properties of this filter are determined by the plant species, and depend mainly on the maximum size of the plant organs A clear correlation is found between the maximum size of the plant leaves and the frequency, from which the filtering capacity of the plants starts Also, a correlation could be detected between the total biomass of a specific plant species and the noise ’’attenuation’’ in the 1/3‐octave bands that are examined The total noise attenuation caused by the vegetation depends on the spectrum of the noise: the sound pressure level of a noise spectrum with high levels in the high frequencies w

Techniques For Speckle Noise Removal

Abstract: In this paper, several techniques to reduce speckle noise (more generally signal independent multiplicative noise) in images are studied. The techniques include gray scale modification, frame averaging, low-pass filtering in the intensity and density domains, and application of the short space spectral subtraction image restoration technique in the density domain. Some discussions on the theoretical basis of the techniques studied are given and their performances are illustrated by way of examples.

Zero-crossing study on dynamic properties of speckles

Abstract: The zero-crossing problem is studied for the purpose of investigating the dynamic properties of speckle produced in the diffraction field by a moving diffuse object under illumination of coherent light. The zero-crossing method is applied to the time-differentiated speckle intensity fluctuations and studied in some detail with respect to the influence of noise and the low-pass filter used for suppressing the noise. From the theoretical and experimental studies, the velocity of the moving object is found to be accurately determined by measuring the number of zero-crossings per second of the time-differentiated speckle intensity fluctuations when both the optical configuration used for producing speckles and the characteristic of the low-pass filter for suppressing the noise are known beforehand.

Airframe Noise Reduction Studies and Clean-Airframe Noise Investigation

Abstract: Acoustic wind tunnel tests were conducted of a wing model with modified leading edge slat and trailing edge flap. The modifications were intended to reduce the surface pressure response to convected turbulence and thereby reduce the airframe noise without changing the lift at constant incidence. Tests were conducted at 70.7 and 100 m/sec airspeeds, with Reynolds numbers 1.5 x 10 to the 6th power and 2.1 x 10 to the 6th power. Considerable reduction of noise radiation from the side edges of a 40 deflection single slotted flap was achieved by modification to the side edge regions or the leading edge region of the flap panel. Total far field noise was reduced 2 to 3 dB over several octaves of frequency. When these panels were installed as the aft panel of a 40 deg deflection double slotted flap, 2 dB noise reduction was achieved.

Noise transmission into a light aircraft

Abstract: An analytical study on noise transmission into a cabin of a twin engine G/A aircraft is presented. The solution of the governing acoustic-structural equations of motion is developed utilizing modal expansions and a Galerkin type procedure. The exterior noise pressure inputs are taken from available experimental data. A direct comparison between theory and experiments on cabin noise levels is given. Interior noise reduction by stiffening, mass addition, and damping treatments is investigated. It is shown that a combination of added mass and damping could significantly reduce interior noise levels for this aircraft.

Two-stage adaptive noise cancellation for intermittent-signal applications (Corresp.)

Abstract: A novel two-stage adaptive signal extractor for intermittent signal applications is presented. If the presence and absence of the signal can be detected, the first stage will adapt only while the signal is absent and thereby effect a reduction in noise, whereas the second stage will adapt only when the signal is present and thereby effect a reduction in the distortion caused by the gust stage. Bounds on performance are derived, and performance improvement relative to a conventional one-stage adaptive noise canceller is assessed.

Nonlinear temporal filter for television picture noise reduction

Abstract: A conventional recursive interframe lowpass filter for 625 line 5.5 MHz monochrome television is modified so that its attenuation of frame differences is instantaneously dependent on their amplitude. This results in improved rendition of motion when compared with the original design. Performance is assessed by objective measurement of noise attenuation for a range of input noise levels and nonlinear characteristics, and by subjective opinion tests on pictures containing noise and movement.

Threshold Selection for Line Detection Algorithms

Abstract: Local operators are used to detect linear features in Landsat data for an area where such features are typically less than 1 pixel in width. A modification to existing techniques is made which gives improved results. The choice of threshold for the detector algorithm is investigated by considering line and background intensity, linewidths, and line alignment with respect to the pixel boundaries and spatial autocorrelation in the data set. It is found that results will always contain a significant amount of noise. Two postprocessing techniques are described which reduce this noise by utilizing contextual information in the data.

High resolution 2-D spectral analysis at low SNR

Abstract: This paper presents a fully two-dimensional high-resolution spectral analysis technique The method consists of extrapolating observed data beyond the observation window by means of 2-D least squares prediction filters High-resolution spectral analysis is then obtained by a discrete Fourier transform of the extrapolated data Previously, methods of obtaining a high-resolution spectrum analysis on 2-D data have applied 1-D high-resolution analyses sequentially to each dimension The fully 2-D method presented here permits the use of nearly the square of the number of extrapolation coefficients that can be used by the sequential 1-D analyses The advantage of the new procedure is that more coefficients permit extrapolating more 2-D sinusoids in the data and also provide reduced sensitivity to noise, thereby allowing operation at lower SNR's A second technique for improving the performance of high-resolution spectral analysis in a chosen region of the transformed data is also presented The technique consists of filtering the data with a 2-D FIR bandpass filter prior to the high-resolution transform This method is also effective in reducing the sensitivity of the high-resolution analysis to noise and other sinusoids

Construction of a phase-inverting grating and its use in a deblurring filter.

Abstract: A method of generating phase-inverting grids for use in image deblurring is described. We have also made an amplitude filter for correcting motion blurred images. This was used along with the phase-inverting grid to deblur motion blurred pictures. Experimental results are presented. It is shown that increasing the noise term in a Wiener filter helps in the reduction of noise but occasions loss of resolving power.

Coherence Improvement in White Noise Analysis by the Use of a Repeated Random Sequence Generator

Abstract: A device is described which allows the averaging of the output of an unknown system in response to identical bursts of pseudorandom noise. The use of this technique produces an improvement in the measured coherence function for the system and a reduction in the variance of the estimated system parameters.

Engine Noise Reduction by Structural Study of Cylinder Block

Abstract: A structural study of the cylinder block was made using a 4-cylinder, 1,800 cc gasoline engine with an aim toward reducing engine noise. First, we studied the relationship between cylinder block vibration and radiated noise, and also the principal component modes of noise and vibration. From the results obtained, it become clear that engine noise could be reduced by suppressing the basic natural vibration of the cylinder block. Alternative shapes of engine blocks were examined. Trial cylinder block was built into an engine. We were able to reduct the noise of the engine proper 2.5db-A with a weight increase of about 3%.

Adaptive enhancement of signal-to-noise ratio in television imagery

Abstract: A noise reduction filter for a television receiver in which two running averages of video signal amplitude are generated over regions of the video picture where the brightness level is substantially constant. One or the other of the averages is used to control intensity to obtain a reduction of random noise in the video signal. In areas of the picture where rapid changes in intensity occur, the averages are not used in favor of the unmodified video signal.

Noise control prediction for high-speed, propeller-driven aircraft

Abstract: An analytical study is described which explores add-on treatments and advanced concepts for the reduction of noise levels in three high-speed aircraft driven by propellers. Noise reductions of 25 to 28 dB are required to achieve a goal of an A-weighted sound level not greater than 80 dB. It is found that only a double-wall system, with a limp inner wall or trim panel, can achieve the required noise reductions. Weight penalties are estimated for the double-wall treatments. These penalties are 0.75% to 1.51% of the aircraft takeoff weight for the particular baseline designs selected.

Acoustic measurements of three Prop-Fan models

Abstract: Results of NASA sponsored acoustic tests of three 2 ft. diameter models of the Prop-Fan (a small diameter, highly loaded, many-bladed variable pitch advanced turboprop) are presented. The highly swept model designed for noise reduction produces substantially less near field noise at simulated 0.8 Mach number cruise conditions than the unswept or slightly swept models. It also produces less far field noise at conditions simulating takeoff and landing. The noise reduction mechanism is discussed. Correlation between harmonic noise measurements and theoretical predictions and between measured and predicted acoustic pressure pulses is good. Shadowgraph measurements which show the location of blade associated wave patterns were obtained. Predicted and measured wave locations show good general agreement. Full scale near and far field noise is predicted.

Chromatographic analyzer detector and method

Abstract: An optical absorbance detector which can be used in process chromatographic analyzers is provided Improvements are provided in noise reduction, temperature stability, operator convenience and construction Noise reducing features include electrical signal filtering and optical system alignment Temperature stability features include an electronic preamplifier inside the oven and a temperature controller to maintain an integrated circuit at a constant temperature Operator conveniences include built-in calibration for electronic circuits and easy optical filter replacement Construction features include explosion resistance and small size

Noise reduction unit for automobile audio equipment

Abstract: PURPOSE:To warrant the audio characteristics pleasant in actual sence without intermittence of audio output at noise mixing, by controlling the variable low band filter with the signal adding the output of the noise detection circuit and field strength detector circuit. CONSTITUTION:The output of the detection amplifying circuit 3 of AM and FM radio receiver is inputted to the noise detection circuit 6. The circuit 6 detects pulsative noise mixed in the audio signal and consists of the circuit storing the peak value tentatively. Further, the output from the intermediate frequency amplifying circuit 2 is received at the electric field strength detection circuit 7, which outputs the voltage signal inversely proportional to the electric field of received electromagnetic waves. The output of the circuits 6 and 7 is added at the addition circuit 8 and the output controls the variable LPF9. LPF9 adjusts the cut off frequency of the output of the circuit 3 according to the output of the circuit 8 and the speaker 5 is driven via the output amplifier 4. Thus, even at pulsative noise mixing or electric field lowering, although the sound quality is more or less lowered tentatively, no sound is interrupted and pleasant audio performance can be obtained.

Reduction of quantization noise in PCM speech coding

Abstract: A new technique to reduce the effect of quantization noise in PCM speech coding is proposed. The procedure consists of using dither noise to ensure that the quantization errors can be modeled as additive signal-independent noise, and then reducing this noise through the use of a noise reduction system. The procedure is illustrated with examples.

Noise reduction in engine exhaust

Abstract: Noise reduction mechanism for an engine, especially effective during idlingnd operation at low RPM, is disclosed. Under those conditions, engine exhaust noise often represents a predominant part of the total vehicle noise. The noise reducing mechanism comprises a flow-throttling element that substantially closes the main exhaust passage when the engine is in the low-speed range; the exhaust gas and noise is forced to flow through a more effective muffling device to reduce the noise at the exit end of the system. At high engine speeds, the throttling mechanism is deflected to a maximum flow condition for avoidance of undesired back pressure in the exhaust system.

Noise reduction unit

Abstract: PURPOSE:To improve breathing effect by simplifying circuit constitution by performing a band-division process as to only a sum signal, by composing the sum and difference signals as to right and left channels of a stereophonic sound signal to be compressed and expanded. CONSTITUTION:Left and right channel signals from input terminals 21 and 22 are supplied to sum circuit 23 and difference circuit 24; the output circuit 23 is supplied to compressor circuit 25, and that of circuit 24 to compressor circuit 35. This circuit 25 is provided with split filters 26 and 27 dividing each band signal, level sensors 28 and 30 compressing each band signal, VCA (variable gain circuit) 29 and 31, and sum circuit 32 mixing both band signals, thereby performing a band-division process of the sum signal. Further, circuit 35 is provided with level sensor 34 and VCA33 and compression and expansion outputs are applied to tape recorder 40 via amplifier 37, thereby inputting the output of sum circuit 32 to tape recorder 40 via amplifier 36. High-band noise of circuit 23 is modulated by noise of circuit 24 to reduce breathing due to variation in the absolute level of a signal.

Noise eliminating system

Abstract: PURPOSE:To ensure an effective noise elimination by detecting the shift amount when the TV picture is shifted, shifting the 1-frame preceding picture signal by the amount of the shift amount of the TV picture and using this difference of the shift amount to control the coefficient for noise reduction. CONSTITUTION:The noise eliminating circuit consists of input terminal 8, coefficient control circuits 9 and 10, adder 11, output terminal 12, frame memory 13, shift amount compensating circuits 14 and 15 plus subtractor 16 each. In such constitution, the shift amount of the subject is calculated at the 1-frame cycle from the input/output signal of memory 13 and via circuit 14, and the shift amount of the subject is compensated through circuit 15. After this, the difference between the compensated signal and the input signal is calculated by circuit 16, and this difference signal is used to control the coefficient of the circuit which controls the mixture ratio between the TV signals. As a result, the coefficient can be set small like in the case of the still picture, and accordingly the noise can be reduced effectively although the picture has some movement.

Automatic Track Assembly For Thresholded Infrared Images

Abstract: An automatic method for track assembly is presented which can initiate new tracks, assign new measurements to the appropriate track, and eliminate false tracks due to clutter. Consecutive frames of thresholded infra-red images are combined and then screened using a three-by-three window. Successive levels of data processing reduce the noise still further, and in a cluttered environment (noise in 3% of the pixels) , it may be necessary to use three or more levels to eliminate false tracks due to noise. Curved paths and crossing tracks are handled without difficulty, and track-like noise can be eliminated by preprocessing. A special coding scheme has been implemented on an array processor to obtain a processing rate of 160,000 pixels per second, independent of the number of targets. This paper develops theoretical calculations for the probability of false tracks and presents verifying experimental results.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The enhancement of wordspotting techniques

Abstract: This paper presents results of research on the enhancement of speaker independent wordspotting in conversational, telephone bandwidth speech from a variety of talkers. The research involved the comparison of five LPC based parameter sets (filter coefficients, autocorrelation coefficients, cepstral coefficients, vocal tract area functions, and pseudoformants), in three levels of additive white noise, and the evaluation of two methods of noise reduction. The techniques were studied with a dynamic programming based wordspotting system. The performance of the system was measured the percent of keywords spotted with no false alarms. The results show that pseudoformants, without the use of speaker normalization or noise reduction techniques, perform as well as or better than the other parameter sets with these techniques.