Questions tagged [wavelet]

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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275 views

Why does the Stationary Wavelet Transform shift this image?

I am running a stationary wavelet transformation on a brain image. I can't understand why it shifts with each level so that the image is no longer centered. You can see that the X component shifts to ...
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1answer
2k views

Normalized Wavelet power spectrum

I am analyzing the spectral components of a time series using the continuous wavelet transform following Torrence and Compo (1998). I would like to partition the signal variability or spectral power ...
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77 views

How can I get frequency information in wavelet?

I am working in image processing. I am confused while getting into wavelet. I applied the fft2() function on Lena image and I got frequency information for the same. But when I applied bior4.4, a ...
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2k views

How can I specify the scale parameter of the wavelet in PyWavelets (pywt)?

When computing wavelet transforms with PyWavelets (Discrete Wavelet Transform in Python), e.g. ...
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1answer
13k views

Feature extraction/reduction using DWT

For a given time series which is n timestamps in length, we can take Discrete Wavelet Transform (using 'Haar' wavelets), then we get (for an example, in Python) - ...
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Estimate the type of wavelet transform in receiver side

Suppose that a signal is decomposed by using discrete wavelet transform (DWT) and transmitted. Is it possible for receiver to find which type of wavelet is applied in transmitter side ? I mean, if ...
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770 views

Intuition behind the Continuous Wavelet Transform?

I was thinking sometime back about how to explain the Continuous Wavelet Transform ELI5. So this is what I came across. The correlation of two exact signals is 1. So if I have an input signal $f(x)$ ...
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3answers
4k views

When can we write Heisenberg uncertainty Principle as a equality?

We know that Heisenberg uncertainty Principle states that $$\Delta f \Delta t \geq \frac{1}{4 \pi}.$$ But (in many case for Morlet wavelet) I have seen that they changed the inequality to an equality....
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1answer
332 views

use wavelet for improving spectral resolution

let us consider following code ...
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2answers
222 views

Does Increasing Resolution Lead to Have a Poor Resolution?

As it has proven in some paper and books the time and frequency resolution of Morlet wavelet is : $\Delta t=\frac{f_c\sqrt{f_b}}{2f_i}$ $\Delta f=\frac{1}{2\pi f_c \sqrt{f_b}}$ I don't know how ...
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2k views

Morlet wavelet time and frequency resolution

I want to calculate Morlet time and frequency resolution. the Morlet wavelet function is define as : $\psi(t)=\frac{1}{\sqrt{\pi f_b}}e^{j2\pi f_c}e^{-t^2/f_b}$ Note: I know the answers, but I don't ...
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973 views

CWT for filtering / feature extraction

I had asked a question last night in regards to how to process my data (Noise rejection / feature extraction) but I have a more specific question now that I hope someone can answer. As mentioned in ...
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1answer
185 views

Noise rejection / feature extraction

I'm hoping someone could point me in the direction of some signal processing methods to clean up my data. I'm collecting physiological data from human muscle (lower leg; gastrocnemius) during walking/...
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1answer
148 views

denosing given signal using wavelet

let us suppose that we have given following model $y(t)=A_1 \sin(\omega_1*t+\phi_1) + A_2 \sin(\omega_2*t+\phi_2) + A_3 \sin(\omega_3*t+\phi_3)+ \ldots +A_p \sin(\omega_p*t+\phi_p)+z(t)$ where $z(t)...
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1answer
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Obtaining beat histogram using Tzanetakis algorithm

I am working to make a music player with automatic genre classification application in Java. On Google searches I mostly found the works of George Tzanetakis who describe an algorithm from Music Genre ...
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1answer
7k views

Wavelet thresholding

What is the difference between soft thresholding and hard thresholding. Where we use soft and hard thresholding in image for denoising. I understand that in hard thresholding, the coefficients below ...
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3answers
18k views

Continuous Wavelet Transform with Scipy.signal: what is parameter “widths” in cwt() function? How do time-frequency?

I search to display a time-frequency signal with an original discrete temporal signal (sampling step = 0.001sec). I use Python and the library Scipy.signal. I use the function ...
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Fast Fourier Transform and Clustering of Time Series

I'm making a project connected with identifying dynamic of sales. That's how the piece of my database looks like: There are free columns: Product - present the group of product Week - time since ...
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3answers
2k views

use wavelet transform to extract frequencies from given signal

let us suppose that we have following signal values,which consists by deterministic components and random noise(white noise) ...
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172 views

Algorithms for removing oscillations?

I am interested in removing oscillations from a signal to capture the lower-frequency variations, similar to the objective of this problem. The oscillations vary in frequency in the time domain, so ...
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2answers
6k views

Disadvantages of wavelet transform

I have a question related to wavelet transform: we know that while the Fourier transform is good for a spectral analysis or which frequency components occurred in signal, it will not give information ...
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2answers
220 views

Is there any difference between the 2D continuous and discrete Gabor filter when it comes to MATLAB implementation

I want to know the difference between the 2D continuous and discrete Gabor filter when it comes to Matlab implementation. I found many files related to 2D Gabor filter on Mathworks File Exchange but I ...
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375 views

Causal Wavelet Decomposition

I've seen the use of a Causal wavelet mentioned a few times but have never seen any examples of them in use with Matlab. Is it possible to to perform a Wavelet Decomposition using a causal wavelet i....
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1answer
226 views

Convolve a minimum phase wavelet with delta peak

let's assume I have two time series: one with a delta peak at position $x$ and another time series with a minimum phase wavelet that starts at time $y$ with a maximum peak at position $z$. Now, when ...
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157 views

Derive Maximum of zero phase rotated wavelet from rotated wavelet

I have one question concerning phase rotation of signals and I am not sure wether it works or not: Let's assume we have a zero-phase wavelet x(t) i.e. Ricker wavelet. Unfortunately, in our ...
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3answers
2k views

Convolution of Signal with a Wavelet

I know that the complex wavelet transform is given by $$\int_{-\infty}^{\infty}f(x)\psi^*_{s,u}(x)\,dx$$ where $f$ is the signal, $\psi_{s,u}(x)=\frac{1}{\sqrt{s}}\psi(\frac{x-u}{s})$ is the wavelet. ...
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1answer
148 views

Suggestions for FFT based tools to analyze music - Preferably MATLAB/free software packages [closed]

I am interested in analyzing full length songs for general features of the track which are not otherwise apparent. For e.g., I want to look at various parts of the song with time-frequency plots/...
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3answers
7k views

Why does a narrower window in a Fourier transform or STFT give poor frequency resolution?

In theory of FT(Fourier transform) and STFT(Short Time Fourier Transform) it is said that "A wide window gives better frequency resolution but poor time resolution. A narrower window gives good time ...
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2answers
466 views

Combining two images

I am working with speckle noise reduction in ultrasound images. I have used wavelet transform for removing the noise by eliminating certain frequencies in order to eliminate any existing noise. Since ...
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2answers
1k views

Fourier Transform of Morlet wavelet Function?

As you know the Morlet wavelet function is given by: $$\frac{1}{\sqrt{\pi f_b}}e^{\frac{-t^2}{f_b}}e^{j2\pi f_c}$$ The Fourier transform of this equation is: $e^{-\pi^2 f_b(f-f_c)^2}$ (is it right)? ...
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4answers
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Why does the high frequency component of an image contain more noise?

I am working with wavelet transforms. When we apply a discrete wavelet transform to an image, it decomposes into four components named the approximation component, thevertical component, the ...
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2answers
171 views

mean of wavelet for image processing

For many papers which talks about using wavelet transforms for feature detection in image processing, it is stated that it is advantageous for the wavelet to have zero mean? Why is this so? Thanks in ...
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243 views

How can I change the frequency band ($\tt Fb$ parameter) using $\tt cwtft$? [closed]

MATLAB's implementation of cwt uses the complex morlet wavelet as: psi(x) = (pi*Fb)^(-0.5)*exp(2*1j*pi*Fc*x)*exp(-(x^2)/Fb); ...
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160 views

how can i call the input data in wavelet transform and generate code for gabor wavelet manually? [closed]

I am an ECE student, and i am doing my project I want to generate a code for gabor wavelet transform. I have no idea could you help me with a sample program I have DNA as input sequences and how ...
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2answers
413 views

Need to learn wavelet, suggest steps and resources [closed]

I am looking for a good introduction to wavelets and wavelet transforms. that covers the following: Vector Spaces – Properties– Dot Product – Basis – Dimension, Orthogonality and Orthonormality – ...
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529 views

Shifting of Shift-Invariant Wavelet Transforms

Main Question: Why would iterative wavelet/inverse-wavelet transforms cause a shift along the x-axis for undecimated (shift-invariant) wavelet transforms? I am attempting to remove backgrounds from ...
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1answer
832 views

Inverse of Wavelet Transforms - Background and Noise Removal

Main Problem: How can you inverse Wavelet Transforms (Using the data given by signal.scipy.cwt) I was wondering if anyone understands the ...
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1answer
108 views

Are all isotropic bandpass filter kernels, wavelets?

Are all isotropic bandpass filter kernels, wavelets? Are there any properties that the radial frequency profile has to meet to be considered a wavelet?
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2answers
182 views

How do I implement the CDF wavelet inverse?

I understand and have implemented a 2D discrete wavelet transform that uses a Haar wavelet to process images. Now I would like to implement a 2D Cohen-Daubechies-Feauveau wavelet transform, but I am ...
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1answer
115 views

Error bounds in signal compression represented by truncated Moore-Penrose biorthogonal bases using von Neumann wavelets

I was reading and trying to reproduce the results in the arXiv preprint of Periodic Gabor Functions with Biorthogonal Exchange: A Highly Accurate and Efficient Method for Signal Compression by Asaf ...
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1answer
505 views

gabor wavelet and gabor transform

I was reading a paper 'A Flexible Framework for Local Phase Coherence Computation' (paper URL) on using wavelets for local phase coherence. I just want to be sure. Is the gabor wavelet the same as the ...
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3answers
390 views

Relationship between windowed fourier transform and wavelet transform

I was reading on windowed fourier transform and wavelet transform, and i was thinking that the windowed fourier transform is a subset of wavelet transform. Is that true?
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166 views

How to undecimate and make shift invariant a Dual-tree Complex Discrete Wavelet Transform in R

I have the following vector and wavelet transform (from R waveslim package) ...
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1answer
96 views

Two-dimensional wavelet analysis

Could you tell me why wavelets without scaling functions can't be used for two-dimensional analysis? What is the role of scaling function?
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1answer
937 views

Denoise EEG signal by using Daubechies function

I have an EEG signal and it contains eye blink artifacts. I read some references and know that it is possible to detect eye blinks and remove them by using wavelet transforms, but I don't know that ...
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1answer
275 views

How can a zero-padded length n signal be truncated to n coefficients from which a signal can be reconstructed?

A wavelet transform is defined for infinite length signals. Finite length signals must be extended in some way before they can be transformed. I know that periodic replication and zero padding are ...
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1answer
95 views

Get spectral picture from a wavelet transform

According to my previous question, I have changed the generate command to: y=generate1(100,1000,1); and got the following picture: Now I want to test a wavelet ...
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1answer
2k views

Help me with BM3D algorithm's aggregation scheme

BM3D is considered state of the art in Image Denoising. I am trying to implement the algorithm in Matlab. Right now, I am done with the 3D wavelet transform in the first step, and to be precise, the ...
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1answer
827 views

What are the main advantages and disadvantages of the lifting scheme?

Can anybody tell me the advantages of the lifting scheme and why it is better then a normal filter bank?
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629 views

Cross correlation coefficient using MATLAB

Actually I want to calculate the cross correlation coefficient of any signal on comparing with all mother wavelets like Morlet, Daubechies using MATLAB.

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