A wavelet is a wave-like oscillation with an amplitude that starts out at zero, increases, and then decreases back to zero.

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Question about vanishing moments in wavelet tranforms

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 ...
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What are the spike removal techniques in matlab without using filters

output from wavelet filter using daubechies 4 wavelet. Using wavelet filter this is the output obtained. The problem is elimination of the spikes at 0.023,0.043,0.063 and so on. Please note: no ...
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64 views

Daubechies wavelet transform

i have N samples obtained by sampling a signal with lot of frequency contents. How will i apply daubechies wavelet transform to obtain the frequency and its location? i need to write a program which ...
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7 views

Interpretation of Diagonal detail wavelets

I am a statistics grad student, and I have just begun exploring the topic of wavelet regression (specifically, Haar wavelets for discrete functions). I understand the generalization from a one ...
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14 views

Undecimated discrete wavelet transform in Python and Matlab

Loosely based on the above figure: I need to make an array like this: array = [(image),(1,ll),(1,lh),(1,hl),(2,ll),(2,lh),(2,hl)] Here, image is a numpy 2D ...
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dyadic discrete wavelet analysis and normality

I have read some documents about wavelet analysis, i undrestood that dyadic wavelet analysis 2^n stationarize series and decorrelate coefficients, and the coefficient are constructed based on the ...
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24 views

Cohen-Daubechies-Fauraue 7/9 wavelet in Matlab

I just want to ask what the wavelet filter name used for Cohen-Daubechies-Fauraue 7/9. what name should I used in 'wname' when I want to use this type of wavelet in Matlab. some say that it is ...
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1answer
13 views

Compression Ratio in ECG compression using Wavelet Decomposition

I have compressed and reconstructed an ECG signal using Wavelet Coefficient. In compressing part, many of Wavelet Coefficient have set to zero. for example, if in original ECG, 5000 wavelet ...
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1answer
36 views

How to do edge detection using Curvelet transform?

I wanted to use Curvelet thresholding for edge detection, that is first take discrete curvelet transform then choose coefficient which are for curve and then reconstruct back to get an edge map. ...
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74 views

Is R suitable for digital signal processing

While asking a question about representing large time series in R I was discouraged from using R for digital signal processing. I understand that R is geared towards statistics. However, a signal is ...
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1answer
64 views

Optimized 2D wavelet transform using FFT

I'm currenty aiming to optimize my fast wavelet transform (FWT) algorithm for 2D signals (images). It works as follows: one iteration of 1D FWT does convolution of 1D input data with a selected 1D ...
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1answer
61 views

Implementing wavelet transform for finding transients in the power supply

I am new to the concept of wavelet transforms. Can somebody please help me in understanding this ? and also how to implement it in c. Is Short term Fourier transform more efficient than Wavelet ...
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19 views

How to choose a wavelet order

I'd like to perform the DWT on a signal in order to find the time-frequency information. I've read from a textbook that the coiflet performs best on this type of signal (ECG), I guess due to the shape ...
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29 views

This is an expression for the computation of kurtosis.

However, I don't understand what the subscript '4x' or the parameter (0,0) stand for. Could anyone explain ?
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2answers
40 views

stationary vs. undecimated wavelet transform

I have a little bit confused on the difference between stationary wavelet transform and un-decimated wavelet transform. So, can anyone tell me, if there is a difference between them?
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1answer
19 views

Getting frequency content at different times from discrete wavelet transform coeffs

After being away from DSP for a long time, I am trying to familiarize myself with wavelet transform. Here is what I (think) have understood so far: Wavelet transform provides you high time ...
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24 views

Plotting the log- log plot of scalogram of Continuous wavelet transform

I'm new to DSP stack exchange also I'm posting a question for the first time. now I have written the following code to find the Wavelet transform coefficients using the standard cwt function of the ...
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1answer
19 views

change the central frequency of a wavelet

I am using the discrete meyer wavelet in MATLAB for time series decomposition. I would like to change the central frequency of this wavelet but I do not know if this is possible or if I would need to ...
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13 views

Finding the original signal from the CWT Scalogram?

I have a Time-Frequency Representation (TFR) of a signal using Complex Wavelet transform with a half wavelet length of 6, I was wondering if there is a way to calculate the original time-domain data ! ...
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30 views

Is this a valid thresholding approach?

I am using a wavelet transform and am testing the following approach to thresholding: All coeffients (whatever their value) after the first N are set to 0 So if my timeseries window is 128 ...
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1answer
52 views

Wavelet decomposition

For the following code, X=[2 2 3 100 4 0 98 100 90 2 3 67 98 0 6 6 89 9 21 78] [C,L]=wavedec(X,N,'db1'); where N is the ...
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44 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
28 views

2D DWT Image Issue

In the literature, I see that a 2D signal can be transformed by first doing a 1D transformation on each row of the matrix followed by the same procedure on each column. It seems that $k^{th}$ level ...
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109 views

Plotting Discrete Wavelet Transform in Python

I'm using Pywavelets to perform a discrete wavelet transform on a signal, which returns the approximation and detail coefficients as a list of float64 1d arrays with increasing size. I was wondering ...
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217 views

Why is a wavelet transform implemented as a filter bank?

The mother wavelet function $\psi(t)$ must satisfy the following: $$\int\limits_{-\infty}^{+\infty} \frac{|\psi(\omega)|^2}{\omega} d \omega < +\infty,$$ $$\psi ( \omega ) \bigg|_{ \omega =0} ...
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14 views

How to properly explain that computing wavelet at fine scale reveal localized high frequency component

I wonder if it is fair enough if I try to follow "Wavelet Tour of signal processing" which apply the Parseval formula: $$ Wf(u,s) = \langle f,\psi^{u,s}\rangle = \int f(t) \bar{\psi}^{u,s}(t)dt = ...
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55 views

Time-Frquency Resolution issues

While Im studying wavelet transform, I have this questions in my mind which can't find it's answer: I understand that when we take longer time windows and take the fourier transform we would suffer ...
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15 views

How accurate is Wavelet packet decomposition for emg signals with frequencies from 10 to 40 Hz?

I have an electromyographic signal sampled at a frequency between 10 and 40 Hz in a time window of 300ms. Is wavelet packet decomposition adequate in order to perform features extraction for ...
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178 views

How to use wavelet decomposition for feature extraction (of fMRI images)?

I have a dataset consisting of fMRI images (from mice) which are divided into 4 groups (different drug dose levels applied). Each fMRI image is 4D, that means each voxel is a time series. For each ...
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1answer
57 views

Opposite of wavelet transform?

Wavelet transform gives good time resolution for high-frequency events and good frequency resolution for low-frequency events. => I want to have complete opposite of wavelet transform, where I get ...
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75 views

Generating Wavelet family matrixes

We have unnormalized Haar matrix which, is for example, H4=[1 1 1 1;1 1 -1 -1;1 -1 0 0;0 0 1 -1] After normalizing it, we use for haar transform. I know how to ...
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40 views

Singularity Detection from 2D Wavelet Modulus Plot

I was wondering if I could get some tips/resources on how to pick out the singularity from my 2D Continuous Wavelet Transform Coefficient Plot (scalogram) using the Gaussian Derivative as the ...
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93 views

Frequency Spectrum through Wavelet Transform in Matlab

I have an EMG signal and trying to find out frequency domain features. I am using DWT for this purpose. It gives out coefficients in approximate and detail matrices. Now, I want to use detail coeffs ...
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36 views

Can we extract phase from higher scales within the CWT?

I have found that I can extract phase from scales higher than those located at the ridge peak of the CWT. I should point out that I'm using the analytic signal and a real wavelet. I find the ridge ...
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74 views

Properties of a custom wavelet family for continuous wavelet transform

First of, I'm new to signal processing. I have a signal which is a linear composition of several basis signals, whereas the same basis signal can occur several times, that is translated, but not ...
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1answer
213 views

Issues with the smoothing operator in coherence estimation using the complex Morlet (Gabor) wavelet

The goal I wish to compute the coherence estimate using the continuous wavelet transform (CWT) of a real-valued signal with the complex Morlet (a.k.a. Gabor) wavelet. I compute the cwt of the signal ...
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1answer
565 views

Wavelet-based C/C++ Peak finding libraries

What wavelet-based peak finding functions are there for C++? I'm looking for something similar to: http://docs.scipy.org/doc/scipy-0.15.1/reference/generated/scipy.signal.find_peaks_cwt.html. ...
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168 views

Comparison between 2 images in Frequency domain

As you can see there are 2 images from the Tom and Jerry cartoon program. In the 1st image both Tom and Jerry are present. But in the 2nd one,only Tom is present.Now,we can clearly see this ...
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4answers
167 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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2answers
86 views

Compare between JPEG and JPEG2000

JPEG image compression is Fourier based DCT while modern image compression technique like JPEG2000 is based on more multi-scale technique like Wavelets.I want to know how Fourier and Wavelets are ...
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23 views

how to choose a appropriate wavelet basis

everyone ,I'm not really undertand the theory of wavelet transform.I just want to use the tool to do some work about signal filtering .Now I have a set of signal ,I have tried in FFT ,but I haven't ...
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1answer
62 views

what is the delta parameter in scal2freq?

I am running complex morlet (cmor1-1.5) wavelet transform. I want to have the transformation for the range of [1,150] Hz whit step of 1 Hz. I want to use ...
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1answer
32 views

How does a wavelet help in image compression?

I understand how the discrete cosine transform is used in image compression in standards like JPEG. However, the concept of wavelets is a mystery to me. I do know that wavelets are functions that have ...
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44 views

Fractal Modulation Implementation

I would like to get help/assistance from whom could support me. I am trying to simulate the Fractal Modulation where the modulation and demodulation equations defined as: Modulation Equation ...
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52 views

What is the difference between Haar transform and Haar wavelet transform?

What is the difference between Haar transform and Haar wavelet transform? Haar transformation is a particular matrix multiplication. Haar wavelet transform is realised as filter banks. So is it ...
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1answer
31 views

How to cover all spectrum in wavelet when it which is behalved?

As I know , wavelet decomposition behave with halve. I mean that a way like this HH HL LH LL. But I wonder, how to corver the all spectrum when it was halved? I think if it want to all cover spectrum ...
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15 views

What is meant by “complete set” in the context of affine wavelets?

In the book by Sayood on compression, he says "if the set is complete, it is called affine wavelets". I want to know what is meant by completeness of wavelets.
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66 views

Why not stop with the first level decomposition in wavelet?

Typically, We do wavelet decomposition with the last one level. But I wonder, why do decomposition withh the last one level? In the other word, why not stop with the first decomposition level?
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507 views

What is the scaling function and wavelet function at wavelet analysis?

I'm trying to looking the meaning and functionality about scaling function and wavelet function at wavelet analysis. I have googling already. But I can't find and understand the meaning. What does ...
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29 views

Matrix expansion into bases

I have an image (that is a matrix), let's say of dimensions NxN. I then want to expand this matrix into M basis matrices (for the moment I'm still unsure how many M of these basis matrices I should ...