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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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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4answers
53 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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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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46 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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13 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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23 views

How to do wavelet decomposition in Matlab?

I want to apply a wavelet decomposition on a vector x using Matlab wpdec function. How can I retrieve from this the approximation and detail coefficients at different decomposition levels?
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50 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
45 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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34 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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15 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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37 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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27 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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1answer
60 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
140 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
211 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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2answers
114 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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3answers
83 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
59 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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13 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
41 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
30 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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30 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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29 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
28 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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1answer
60 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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1answer
55 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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24 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 ...
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1answer
141 views

How to find phase values on precise pixel locations of a given Image? [closed]

I have computed magnitude and phase spectrum of cameraman Gray scale image using fft function. Here, we get magnitude and phase spectrum of the whole image. .Please see the reconstruction of image ...
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1answer
70 views

Where is the “time and frequency” in a Discrete Wavelet Transform?

The DWT is motivated by the ability to see signal in time and frequency at the same time, if I understood that correctly. I am using the following Matlab commands for some signal x: ...
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54 views

Time frequency representation of DWT coefficients in Matlab

I am using discrete wavelet transform to analyze an audio file. I can calculate the dwt coefficients and the inverse dwt works fine. What I want to do now is to visualize how different coefficients ...
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0answers
20 views

Wavelets and filters?

I've tried using the search function to answer this question, but haven't found any explicit answers. I'm trying to study Gabor and log-Gabor filters. Most of the content I find is on Gabor wavelets ...
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72 views

Multilevel one-dimensional wavelet analysis-Downsampling

I'm a complete novice to digital signal processing and I am not completely sure about down sampling using wavedec and appcoef in 1D dwt. I am analyzing sound signal and I would to compere and see how ...
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1answer
28 views

How matching pusuit algorithm works

I could infer from books and wiki that a matching pursuit finds signal approximations from a redundant dictionary. Let f be the signal, ai be the basis and Ri be the residue.. here we choose the inner ...
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63 views
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69 views

Image denoising algorithm in matlab

I'm trying to denoise a grayscale image using the two level denoising algorithm as shown in the following block diagram. I used wiener filtering for denoising.Code is given below. ...
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15 views

Wavelet packet transform (WPT) features dimensionality

Just a question that could be trivial for someone but I'm doubtful. Let's say that I have a signal, e.g. electromyography signal, of length $300$. If I apply a WPT, how can I define the dimensionality ...
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11 views

DIrectional data in image

What is mean by directional content as perceived in Contourlet transform of image/signal processing? Wavelet transform cannot capture directional information.
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37 views

Unable to obtain accurate amplitude using Continuous Wavelet Transform

I'm doing an analysis of pre-known signal (example in Mathworks), consisting of two sinusoids, one at 100Hz and the other at 50Hz. I applied CWT to the combined signal and the amplitude (~7 for 50Hz ...
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54 views

Complex Morlet Wavelet piano sound analysis

my project is monophonic music transcription I am using complex Morlet wavelet but over the 1000 Hz complex Morlet does not give all results right, my code is like that ; ...
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55 views

How can I get the inverse of complex continuous wavelet transform in matlab?

There is a function in matlab, namely "CWT" that yields the complex coefficients of the wavelet transform for a certain complex mother wavelet. However, it seems the inversion is not a straightforward ...
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71 views

Resolution problem of high frequency components in wavelet domain

I am trying to exploit the sparsity of Chirp signal in wavelet domain. But I have trouble working with continuous wavelet transform. For lower frequencies everything is OK, however as frequency ...
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1answer
95 views

denosing using soft thresholding or hard thresholding in matlab

let us consider following code ...
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130 views

Help for programming CWT using complex morlet wavelet?

Here is my code for continuous wavelet transform using complex morlet wavelet. But it's not giving accurate result..Please anybody help to rectify my mistakes..thanks in advance :) ...
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19 views

Is there any wavelet similar to coif2 but with rounder trough at the bottom?

Is there a standard wavelet funtion which is similar to coiflet 2 but with a more blunt or round trough at the bottom? It is like mexican hat wavelet but inverted.
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2answers
77 views

why wavelet coefficients are zeros after decomposition

I am learning wavelet theory for image processing. To understand the theory, I write one Matlab program to decompose one black-white image. The program is as follows ...
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2answers
87 views

Can wavelets be used for complex texture discrimination?

I've recently been studying wavelet analysis with a view to differentiating certain areas of texture images where the texture differs from the background pattern (which is quite random); for example a ...
2
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0answers
45 views

Clarification about wavelet thresholds

I am trying to wrap my head around the original wavelet shrinkage papers of Donoho and others from the mid-90s. There are a couple of curious things that confuse me, and I'd appreciate some input: ...
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1answer
52 views

How convert scal to frequency when use cwt in matlab

I am new in DSP.I have the flowing code t = linspace(0,1,1000); x = cos(2*pi*60*t); CWTcoeffs = cwt(x,1:64,'sym8','plot'); colormap jet; and my output is: ...
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15 views

EZW parent-child relation

I’m trying to learn the EZW principle. I’m having trouble understanding the parent-child relationship. In my case, I want to use it on a 1 dimensional signal. So, let’s say for example a signal of 4 ...