Questions tagged [denoising]

Denoising is a collection of techniques to remove unwanted noise from a signal. Typically this is done by filtering, but a variety of other techniques is available. Often combinations are used in sequence to optimize the denoising.

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On number of samples needed

Suppose we get $m+1$-bit signed noise samples $n_i$ with magnitude of noise as high as $m$ bits. Does averaging say $m\log m$ samples suffice to get average of $n_i$ to magnitude within few LSBs? ...
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Estimating the standard deviation of Gaussian filter from smoothed image

Firstly, let's say that in order to smooth an image, I convolve it with a Gaussian function having standard deviation $\sigma_x$ and $\sigma_y$. I am now interested in knowing if there exist methods ...
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1answer
163 views

Wavelet image denoising: dual-tree versus double-density

What is the main difference between the dual-tree DWT and the double density DWT image denoising techniques? How does the combination of them improve the quality of the denoised image?
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Any examples of analysis in time domain to extact information

I am sending a 20Khz signal from my phone and capturing all the signals while doing exercise above it. Here I have a signal of a person doing "hand scissors exercise" I am doing analysis on how many ...
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79 views

How to preprocess such signals?

I am interested in denoising accerelation measurements, recorded in ambient vibration tests. Such tests consist in recording the vibrations of a mechanical structure, say a table for example. So say I ...
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45 views

Smoothing for damped wave signal (fixed variance noise, but changing SNR)

My colleagues and I are arguing about how to smooth a damped wave signal. This signal is corrupted by white noise of a steady magnitude. However the signal damps out as it goes along. So, the SNR ...
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3answers
1k views

Can I square signal in the frequency domain to reduce noise?

Let's say this is the FFT of my measurements: You can see that there is a clear peak and the rest is noise. I want to reduce noise, so I square the FFT and normalize it: The peaks are now more clear,...
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1answer
548 views

How Does the Non Local Means Filter Work?

As I understand, A local mean filter is the one in which we take a pixel and calculate the mean of color-values of the pixels around them (but in a certain range of area) and the center pixel is ...
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263 views

Audio Denoising - Method which Extends the Naive Noise Reduction

Given an audio signal x[n] sampled at 44.1khz (let's say 1 minute of music or speech) and a noise template noise[n] (let's say 2 ...
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1answer
322 views

spectral subtraction for stationary noise

my recording was suffering from stationary background noise. I used spectral subtraction to remove it. the noise is reduced in loudness but not eliminated completely. before: http://vocaroo.com/i/...
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Gradient of Total Variation (TV) Norm in Total Variation Denoising

In this link, it says that the gradient is as follow The Gradient of the TV norm is $$ \mathrm{Grad}J(f)=\mathrm{div}\left(\frac{\nabla f}{\lVert\nabla f\rVert}\right). $$ From this other link, ...
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1answer
86 views

Can we detect multiple point target within a narrow-band transmit signal?

As I understand matched filter is optimal linear filter for maximizing the Signal to noise ratio (SNR) in presence of additive stochastic noise. Consider a radar/sonar system with narrow-band transmit ...
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178 views

Removing low frequency vibrations from measured signal

Suppose I have two sensors $s_1$ and $s_2$. $s_1$ measures the desired heart signal (with most of the frequency content below 100 Hz), and the other is a reference sensor picking mainly background ...
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250 views

sparse representation for image denoising

When I read papers on image denoising, I always encounter sparse representation. For image denoising, we try to separate image signal from noise. It is assumed that signal is correlated and noise is ...
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498 views

Noisy signal filtering MATLAB

I'm currently working on rectifying a respiratory noisy signal shown below: I've already tried to filter the noise as you can see in the image below (full image): The red one is the noisy signal ...
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2answers
143 views

Why do we assume the matrix of impulse responses to be a Toeplitz matrix during deconvolution

$y(n)$ = output signal $x(n)$ = input signal $\mathbf H$ = system response as a toeplitz matrix $$\mathbf H = \begin{bmatrix}h(0)&&&\\h(1)&h(0)&&\\h(2)&h(1)&h(0)&\\...
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Question about vanishing moments in wavelet transforms

I am reading the book Noise reduction by wavelet thresholding by Maarten Jansen. About vanishing moments, it reads To create a really sparse representation, we try to make coefficients that live ...
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2answers
1k views

How to Subtract One Signal from Another?

I am capturing some body internal signals. I am using 2 identical mics. One captures the in body signal and one open air. I want to remove/delete/subtract the open air signal (noise for me) from ...
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What is the difference between MSE and PSNR of images?

I have some doubts. What is the difference between quality parameters MSE and PSNR? Which is used when? Is there any advantage of PSNR over MSE or vice versa? Also I have heard people saying that ...
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Denoising of Images capture by digital camera using Butterworth Filter

Right now, i am doing a research on how the Butterworth filter can reduce the noise in images captured by digital camera. For start, what i need is images which contain noise in it. My question is; ...
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4answers
546 views

Removing Bounded Noise from an Audio Signal

I'm currently trying to remove some noise from a "contaminated" audio file. From what's given, I know that the noise is isolated to a specific frequency band - that is, from ~1400 Hz - ~1800 Hz. The ...
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190 views

Reducing Pepper Noise from an Image

For an image with pepper noise, presuming it is desirable to reduce the pepper noise, which operations, in which sequence, would you apply? Find an image, add pepper noise, and demonstrate your ...
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150 views

Remove microphone rustle / clothing rustle from raw audio data

Thank in advance for the help. I have several GB's of raw audio data that I have collected as part of a research study. This audio is divided up into individual samples approximately 30 seconds in ...
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3answers
315 views

The model of noise in Image denoising problem

I am studying the image denoising problem. The paper I studied uses Gaussian Noise to model the noise appearing on the image. E.e., If we say $u_g$ is a clean image, then we model the noisy image $u_0$...
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How to derive the results that averaging $N$ signals yields a $\sqrt{N}$-fold increase in signal-to-noise ratio?

If I have understood correctly, averaging $N$ noisy independent segments or signals increases the signal-to-noise $\sqrt{N}$-fold. How does one derive this result?
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185 views

relationship between number of wavelet decomposition level and noise level

I am studying wavelet theory by myself and hope to use wavelet to denoise images. I write one matlab program to watch denoised image. ...
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1answer
55 views

the rate of noise presented in images

I suppose that an image is affected by a multiplicative noise (or additive noise and etc.). I want to quantify and measure the rate of noise (for exemple 1%, 2%, ...,25%) present in an image. I used ...
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730 views

How does spatially white noise differ from diffuse noise

In noise reduction, having read that directivity index is used to reduce diffuse noise and white noise gain reduces spatially white noise, I would like to know the difference between both the noise ...
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234 views

why the ultasound image is noisy by speckle noise?

My first question : I want to know why an image is noisy ?. why the ultrasound, SAR and Laser... images are noisy by a multiplicative noise not an additive noise? Another question : So the ...
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1answer
624 views

Denoise Image with Gaussian Noise Using MATLAB / Octave

I want to remove a noise for an image using MATLAB, when the observed image is $$f=u+v$$ where $u$ is the restored image (is the image i want recovered) and $v$ is the gaussian noise. To restore $u$,...
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42 views

Denoising approach for a combination of several ADC voltage channles

I have 2 ADC channels of constant voltage measurement with small amount of high frequency noise only and no low frequency oscillations. The final signal should be the simple sum of those and denoised ...
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4answers
2k views

implementation of Fourier denoising with hard threshold

I just tried the Fourier denoising method with a hard threshold and my code is as follow: ...
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1answer
165 views

Smooth (not) equally-spaced signal strength data

I'm currently trying to reduce the noise in/smooth sampled signal strength data. The context is that I collected data from a transmitting device using bluetooth - the available data is basically a ...
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5answers
935 views

Removing periodic spike noise from ECG signal

The signal shown in the following figure is collected from a ECG sensor. The spike noise that is observed with a periodicity of 30 seconds was traced to the periodic blip of the LED as it draws ...
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1answer
356 views

How to make a plot of noise standard deviation sigma vs. brightness from a images?

Hi I don't know where to start from. I'm trying to implement a plot of noise with Matlab. I have found a plot of noise standard deviation sigma vs. brightness from a images like this. http://www....
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52 views

Nonlinear tricks for blocking wide band noise

Conventional methods of filtering allow one to block parts of a frequency band while passing others. But thinking outside of conventional means, and perhaps not based on any frequency methods at all, ...
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290 views

Motion Artifact Cancellation from ECG Signal Using 3 Axis Accelerometer Data

I have a ECG signal measured as a test subject is performing 3 different activities - sitting, walking(2mph) and jogging(5mph) and also the corresponding 3-axis accelerometer(X,Y and Z) signals. I can ...
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1answer
223 views

1D filter for speed input and noisy position sensor

I was tasked with designing a filter to smooth out a translating table. The system, we command a speed and a desired position, and measure it with two noisy position sensors. The commanded speed is ...
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1answer
3k views

Calculating SNR for ECG signals

I'm reading through the literature for finding the best way to calculate SNR for a ECG signal. While there are many algorithms for improving SNR, I couldn't find any that details any standard ...
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1answer
367 views

Weighted Nuclear Norm Minimization for Image Denoising

Recently, I saw new published papers like Shuhang Gu, Lei Zhang, Wangmeng Zuo, Xiangchu Feng, Weighted Nuclear Norm Minimization with Application to Image Demonising [pdf]. about denoising images ...
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Removal of noise from vibration recordings

Problem I am analyzing accelerometer recordings that are contaminated by 'spikes' caused by issues in the digital circuitry. The spikes are problematic, because I wish to determine the peak-amplitude ...
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577 views

Duration of unknown rectangular pulse with additive white Gaussian noise

Problem. There is a discrete signal $f[i]$ (example below). It is known, that $f[i]$ have a form of rectangular pulse with additive white Gaussian noise. $f[i] = s[i] + n[i]$, $s[i] = \alpha(\...
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How to remove the noise without destroying the main edge?

I am working on a project. I want to segment a logo from a car and the picture's size is 3648*2432. The logo is selected by the red rectangle. I extracted this area and turn into gray level. The ...
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1answer
431 views

Denoise images with wavelets

I try to understand what following algorithm from this gimp plugin does to denoise an image: ...
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156 views

Adaptive Line noise removal using IIR notch filters

I'm trying to filter out line noise(60Hz and 120Hz) from a EEG signals received over a bluetooth link. I'm proposing to use a IIR notch filter to filter out the line-noise which varies w.r.t to ...
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42 views

Estimating plant parameters from noisy frequecy response data

I have to estimate the parameters of a 1st order transfer function, namely, the coefficients, through experiment. I ran a few experiments and I have a bunch of input-output data vectors. The ...
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2answers
557 views

Adaptive Gaussian Filter for Image Denoising

I am looking for methods to enhance noisy images, where: some pixels in the image are very noise, some other pixels do not contain so much noise. My first thought is to build an adaptive Gaussian ...
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2answers
1k views

Poisson noise and curve fitting - denoise first?

If I have an image that is severely corrupted by Poisson noise, and I want to fit a function to the image, is it "better" to attempt to denoise the signal first before fitting, or should I move ...
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2answers
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Using MATLAB `xcorr()` to Find a Signal Hidden Behind Noise

I am trying to develop some code to find a transient signal in a data set I have. Before I get there however I am trying to write code using simulated data. I first am creating a signal with a ...
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2answers
560 views

Separate Signal Values from Noise

let us consider following graph of singular values i want to make some kind of clustering of these data,namely to seperate main components from non main components,let say signal components from ...