# 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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### Wavelets and bank filters

The wavelet transform has a problem as it gives poor time resolution for low frequencies and poor frequency resolution for high frequencies according to uncertainty conditions. This appears well ...
130 views

### Question about normalization before estimate the spectrum

I work with a Electrophysiologist Team and i have seen something who interrogate me (i'm a noobs in DSP). They acquires a signal into a brain structure (an LFP to be precise) : in a first time they ...
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### Making sense of Haar transform and inverse Haar transform

Yesterday, my teacher taught us about the Haar transform (for pictures). We had to implement it in Python and when I finished I was wondering: what was the point? I can't explain the purpose of what I'...
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### Integer Wavelet with Only Positive coefficients

Is there any Integer Wavelet Transform which produce only positive coefficients? Currently i'm using Haar wavelet but it produces both positive and negative coefficients.
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### Are there analogues to orthogonal transformations in non-orientable surfaces?

I am working on extremely large, symmetric matrices of counts, and attempting to identify patterns/shapes within them. Wavelets are a popular tool in image processing, and have some nice statistical ...
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### Perfect reconstruction of 2 channel filter bank

I am studying Perfect reconstruction of 2 channel filter bank for using Biorthogonal Spline wavelet for decomposing ECG signal. I am using Wavelets and Filter Banks By Gilbert Strang, Truong Nguyen to ...
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### Dimensional analysis in the Morlet wavelet

I'm a complete beginner on signal processing, so please forgive the basicness of this question - but I'm very confused by this. Regarding the Morlet wavelet, Wikipedia says: The wavelet is defined ...
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### Programming the IDWT for image processing

I want to program the 2D inverse discrete wavelet transform (only 1 level) in the case of image processing. In the matlab website there's this diagram: now, I want to program the IDWT with haar ...
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### Real-time wavelet decomposition and reconstruction for ECG feature extraction

I need to locate R-peaks in an ECG signal. I'm using wavelets to extract QRS complexes: First, I decompose the signal using a maximal overlap discrete wavelet transform with the Symlet 4 wavelet. This ...
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### How left out down-sampling in 3D-DWT just on the Z direction

I am working on image processing by a 3D wavelet transform. I have a problem with the classification size of the wavelet coefficients. As you know, when we apply 3D_DWT on the image (for example: ...
284 views

### Why do wavelets integrate to 0 and how do they match a signal?

I have been reading about the Wavelet transform recently and its relationship to the Fourier transform. From what I understand the wavelet transform represents signal data with many short-lived ...
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### Computational burden of EMD/Huang-Hilbert vs wavelet

I am working on an online application of signal processing and pattern recognition. It involves sampling the signal at 2 MS/s, extracting features and classifying. My classifier has pretty good ...
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### Getting started with wavelet-based real-time anomaly detection for temporal signals using Python

I have an anomaly detection problem I wanted to consider addressing in software (python) with wavelets. I’m new to wavelets as well as the python’s spicy.signal wavelet package, let alone with the ...
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### Discrete wavelet transform; how to interpret approximation and detail coefficients?

I am trying to understand Wavelet transform. So far I have understood the basic theory of it. But I am not able to get my head around how to interpret both coefficients. I am using PyWavelets ...
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### How i can create ghost on wavelet or seismic trace and then Deghosting that in MATLAB? [closed]

I want to model a seismic trace or wavelet and then create ghost on them, at the end Deghosting in MATLAB. Can anyone help me please?
630 views

### What are the pros and cons of wavelet for filtering compared to conventional filters?

Wavelets have been widely used in denoising or extracting one specific frequency band of a signal nowadays. However, these can also be done through conventional filters (e.g. butterworth, Chebyshev). ...
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### What is the difference between Constant-Q Transform and Wavelet Transform and which is better

i have been seeking for a better Transform than STFT with high overleaping. The Transform should more suitble for the human auditory system. And i learned that there are at least 3 Methods i may use ...
2k views

### What happens when we reconstruct a signal after its Fourier transform is done and some frequencies are altered? [closed]

Since we loose time information when we take a Fourier transform, what happens if we alter a few frequencies from the transform and then reconstruct the signal, do we get the altered frequency at the ...
254 views

### Inverse wavelet transform on wavelet coefficients

I have a data set which consists of Morlet coefficients for 7 channels in 18 bands. When I try to use inverse DWT in Matlab to get the raw data in time, using this code: ...
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### sparsifying an ECG signal using wavelet

I have an ECG signal, and want to sparsify it using wavelet (DWT) in Matlab. In some paper they use Daubechies wavelet (DB4) with 8-tap filters. but i don't know how to extract the wavelet ...
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### Quadtree decomposition of Discrete Wavelet Transform using bio4.4/CDF wavelet

My problem is pretty basic but fundamental. It relates to the way discrete wavelet transform behaves for biorothognal 4.4 or CDF wavelets. When using most wavelets (e.g., CDF 9/7 or bio4.4 or ...
134 views

### Continuous wavelet transform subsampling at lower frequencies?

I am not completely confident in my understanding of wavelet theory, but since I am currently in the process of creating a CWT scalogram tool, I have to ask: Is there a theorem allowing us to ...
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### What is the meaning of negative second for a Morlet wavelet?

I kind of familiar with wavelet transform (I just used it in code but do not have a deep understanding about it). I've been reading an article and came across this sentence: where 4Fs is the ...
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### Reduce Signal Size to Compare Them

I have multiple experiments and each of them produce several ($k$ for example) binary signals; some artificial example next: I have a metric to compare experiment results but I need vectors of equal ...
927 views

### 2D Wavelet Transform Explanation

I am new to wavelets and for several times I stumbled over these 2D wavelet transformation pictures, but I do not understand how they are created. Can anybody try to explain in his own words how this ...
2k views

### Multilevel partial wavelet reconstruction with PyWavelets

I'm looking for a way to partially reconstruct branches of a wavelet decomposition, such that the sum would recreate the original signal. This could be achieved in MATLAB using: ...
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### Output of MATLAB's two-dimensional DWT function $\tt dwt2$

This is a conceptual doubt about the two-dimensional DWT. I am trying to understand the decomposition step of a two-dimensional DWT. In the MATLAB explanation, the two-dimensional DWT generates 4 new ...
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### Values (amplitudes) of the CWT and their relationship to waveform amplitudes?

I'm coding up a scalogram in C++. Right now it calculates a single row of the CWT matrix and immediately maps it to a line of pixels. Trouble is my colouring scales with the values of the transform ...
284 views

### Is Wavelet Transform better than FT if I'm only interested in knowing the frequencies and not interested of when did they happen?

I'm still in the first stages of learning about these different transformations. But one thing that came to my mind while learning about them is the question above. I learned that ...
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### Relationship between Wavelet transform and Fourier Power Spectral Density

Is there anyway to obtain the Fourier Power Spectral Density from a wavelet transform of a time series? I am particularly interested in this problem because I was wondering if there is any ...
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### Is MATLAB documentation wrong on when to use discrete versus continuous wavelet transform?

I was reading some of the MATLAB documentation and I get confused when reading the part about When is Continuous Analysis More Appropriate than Discrete Analysis? My knowledge before reading the ...
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### Why are wavelet transforms (Multi Resolution Analysis) used more in practice for compression rather than Fourier series?

I know that both Fourier and wavelet can be used for compression of signals. The Fourier series guarantees that it gets the closest approximation of the original signal in the least squared sense. ...
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### Edge map based on a Haar Wavelet Transform

I have been implementing the paper Blur Detection for Digital Images Using Wavelet Transform and was asking myself how the following formula could reconstruct the edges given a Haar Wavelet ...
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### Phase Information at Higher Frequencies in Continuous Wavelet Transform

I'm using the code I found here to compute the wavelet transform of a sine wave with a constant frequency. ...
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### Does SWT/ISWT require intermediate approximation coefficients to represent/reconstruct the original signal?

Taking into account that Stationary Wavelet Transform (Algorithme à trous) is not an orthogonal transform do we need intermediate approximation coefficients for signal decomposition? For example, in ...
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### Additive white Gaussian noise and undecimated DWT

One of the benefits of DWT is that it is an orthonormal transform. There are statements that the energy of noise component mainly concentrates on the high-frequency (detail) part and distributes ...