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Questions tagged [pywavelets]

Python library for wavelets and wavelet transforms.

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Time step (skipping) in CWT function with PyWavelets

I am using cwt function from pywavelet to perform time-frequency decomposition of a large signal (several million samples). The computational requirements for this is huge, sin it performs the ...
Juan Luis Ferrando Chacón's user avatar
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Wavelet transform, scalogram, detail and approximation coefficients

I understand tha the wavelet transform is about computing the coefficients to assign to scaled and translated versions of the chosen mother wavelet. The coefficients measure the correlation between ...
Brett Cooper's user avatar
4 votes
1 answer
141 views

Wavelet basis orthonormality

I recently started learning about wavelet transforms, and there's something that is confusing me. My understanding was that most wavelet decompositions are simply a decomposition of a given signal in ...
Sahand Tabatabaei's user avatar
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Identify variation patterns in image time series

I am working on time series of 12 remote sensing images obtained at irregular intervals. The pixels of all images are of exact same region. Pixels of some areas in these images vary in time with ...
sat_P's user avatar
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PyWavelets CWT : error when differentiating after convolution?

I'm trying to understand the implementation of CWT in PYWT. This topic has already helped me quite a lot but there is still a thing that is unclear to me : why is the result differentiated only after ...
Tanguy Jonv's user avatar
2 votes
1 answer
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Is there a reason why wavelet in continuous wavelet transform are symmetric?

I have looked at several packages to do continuous wavelet transform (cwt), and the usable wavelet families that are available are always symmetric. Is there a reason for that? The kind of signals I ...
Johncowk's user avatar
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Integrating over the translation on a DWT

I'm really a begginer at Wavelet transform and I'm starting to use the pywt module. I have some difficulties understanding the link between the following integral and the coefficients of the DWT: $$ W(...
user68569's user avatar
1 vote
1 answer
275 views

Python's equivalent of MATLAB's cwtfilterbank

I am learning signal processing and would like to know what's the python equivalent of matlab's cwtfilterbank. I looked through pywt but did not find anything. Some ...
JXuan's user avatar
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why is the output length of the inverse wavelet transform the double of my original signal?

I have an input signal of 30000 samples. I perform the Stationary wavelet transform in python to get the 4th level od decomposition. Then I perform an array mathematical operation over the decomposed ...
GGChe's user avatar
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What are frequencies in a scaleogram generated using pywavelet?

I am using PyWavelet to do continous wavelet transform of a 1D signal. The pywavelet continous wavelet transform function works with this line of code: ...
User's user avatar
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3 votes
1 answer
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Why does a signal with constant frequency have spots that changes colors at a specific value of scale (and so frequency) in the scalogram?

I am studying the Wavelet transform and I am considering this example that I took from PyWavelets documentation. The signal in time domain has the following shape: Till the value of zero on the ...
User's user avatar
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Estimation of scaling exponent in the wavelet leaders multi-fractal formalism

I am trying to extract multi-fractal features from time-series data by estimating the singularity spectrum using the wavelet leaders multi-fractal formalism (WLMF) method. Specifically, I want to be ...
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Output of pywt.dwt

I am using 'dwt' function and I can't understand what the values in the approximation and detail lists actually represent. I have read that in each level the function uses high pass filters and low ...
yba's user avatar
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Adjust Wavelet output to CNN

I want to extract features from the signal using DWT and then feed the results into CNN, after calling the 'dwt' library function I got a runtime error. ...
yba's user avatar
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1 vote
1 answer
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Discrete wavelet decomposition over detail coefficients

per my understanding, if we take a 3-level discrete wavelet decomposition (DWT) over a 1-D signal with sampling rate $F_s$, we will get a series of detail and approximation coefficients, ex: [cA3, cD3,...
William's user avatar
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Difference between Discrete Wavelet Transform and convolution

Sorry in advance if my question is too dumb. I'm going through the book of Mallat, and from what I understand, the approximation/wavelet coefficients $a_j[n] = <f, \phi_{j,n}>$ and $d_j[n] = <...
Elenie's user avatar
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Function reconstruction after a DWT

I'm new to this field, my apologies if my question sounds too naive. From what I understood, a function can be decomposed using the scaling function at a given scale $\{\phi_{J, k}\}_{k \in \mathbb{Z}}...
Carline's user avatar
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Pywavelets applied to time series

I'm new on this field. I am applying a discrete wavelet decomposition to a timeseries and the decomposition yields subsets of the data, specifically the half. Nothing wrong with that since that is the ...
Sherwood's user avatar
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836 views

How to get scalogram in frequecy & time from continuous wavelet transform of time series

I have a time series for which I want to apply a continuous wavelet transform and plot the scalogram, where the scalogram is frequency on the y axis and time on the x axis. I'm using pywt's cwt (docs),...
a11's user avatar
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1 answer
327 views

How to do appcoef and detcoef using pyWavelets?

I am new to signal processing and currently doing a school project in wavelet transform using Python. I want to extract all details and approximations (Example: cA2, cA1, cD2, cD1), pywt could return ...
Megan's user avatar
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1 vote
1 answer
247 views

How to plot the shape of a 2D wavelet?

I often see images like this: where on the left it depicts 2D wavelets and on the right curvelets for different scales and locations. How can I visualize different 2D wavelets/curvelets in such a way ...
stish's user avatar
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Pywavelets CWT returning 0 after scale 64

I am running continuous wavelet transform in mexican hat wavelet basis on a data set (with millions of samples) using pywavelets. The command used is ...
Manuel Jenkin's user avatar
1 vote
1 answer
1k views

PyWavelets SWT versus MODWT

I'm just learning about wavelets and the PyWavelets package. I saw a reference to MODWT, which led me to the SO post here and then to this Python package: https://github.com/pistonly/modwtpy What ...
SuperCodeBrah's user avatar
2 votes
0 answers
68 views

Pros/Cons to using Spectral and Diffusive Graph Wavelets

As I understand, there are two major methods of constructing wavelets on graphs. Spectral wavelets, from David K Hammond et. al, and diffusive wavelets from Coifman and Maggioni. I can't quite parse ...
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How is wavelet center frequency computed?

PyWavelets (1) takes index of max DFT magnitude, (2) adds 1 to it, (3) divides by domain, which is the range of input values to the wavelet ("support"). ...
OverLordGoldDragon's user avatar
1 vote
1 answer
1k views

CWT at low scales: PyWavelets vs Scipy

Low scales are arguably the most challenging to implement due to limitations in discretized representations. Detailed comparison here; the principal difference is in how the two handle wavelets at ...
OverLordGoldDragon's user avatar
4 votes
1 answer
2k views

PyWavelets CWT: normalization? Vs Scipy?

Related. The equation being implemented normalizes by sqrt(1 / scale): $$ C_{a, b} = \frac{1}{\sqrt{a}} \sum_k s(k)\left( \int_{-\infty}^{k+1} \overline{\psi \left(\...
OverLordGoldDragon's user avatar
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1 answer
155 views

PyWavelets CWT: resampling vs recomputing wavelet

Related. The implementation pre-integrates a wavelet once, and resamples it at each scale, finally differencing to implement ...
OverLordGoldDragon's user avatar
2 votes
1 answer
3k views

PyWavelets CWT implementation

I seek to understand PyWavelets' implementation of the Continuous Wavelet Transform, and how it compares to the more 'basic' version I've coded and provided here. In particular: How is integrated ...
OverLordGoldDragon's user avatar