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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2answers
260 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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3answers
6k views

Any Open Source Fast Wavelet transform libraries?

I am in need of an open source library for computing Fast wavelet transforms (FWT) and Inverse fast wavelet transforms (IFWT) - this is to be part of a bigger code I am currently writing. The things ...
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1answer
2k views

What does the normalization step of the Haar wavelet transform represent?

When you perform the Haar wavelet transform, you take the sums and differences, then at each stage, you multiply the entire signal by $\small\sqrt2$. When taking the inverse transform, you multiply ...
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1answer
65 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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1answer
453 views

Correct way to implement Discrete and Stationary Wavelet Transform?

Can someone please confirm if this is indeed the correct way to compute DWT: ...
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2answers
352 views

Explanation on Haarlets

Would someone be able to give me some info or a link etc ... regarding haarlets aka Haar wavelet-like features. I'm reading several papers for my master dissertation and several of these papers ...
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1answer
1k views

denosing using soft thresholding or hard thresholding in matlab

let us consider following code ...
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0answers
750 views

How can I identify the damping of the modes in a signal by Cmor wavelet method?

I read several papers which proposed a method to identify modal parameters. such as natural frequency and damping ratio.I've tried to implement those methods by Matlab.but I couldn't get the result.It ...
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2answers
122 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 ...
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1answer
445 views

Denoise images with wavelets

I try to understand what following algorithm from this gimp plugin does to denoise an image: ...
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0answers
61 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
557 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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1answer
442 views

How to narrow the frequency band of a wavelet

I have a ricker wavelet with a dominant frequency of 15 Hz. The fourier transform shows its frequency band is almost to 50 Hz. How can I narrow the frequency band of this 15 Hz ricker wavelet? I have ...
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1answer
114 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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0answers
27 views

Are there condition numbers associated with the STFT, DWT?

Recently I learned that the DFT has good numerical stability since it can be represented as an orthogonal matrix, which has a condition number of 1. Is it possible to represent the STFT and DWT as ...
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1answer
894 views

How can we calculate the frequency response of each filter of a Discrete Wavelet Decomposition filter bank?

I am using the Multilevel Wavelet decomposition. The decomposition results in a filter bank such as the following: Specifically, I am using one of the Daubechies wavelets, ...
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0answers
46 views

Larger image after wavelet reconstruction

Depending on the size of the original image and depending on the kind of padding used during 2D discrete wavelet transform and reconstruction, the reconstructed image has a larger size. Is there a ...
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1answer
174 views

Orthornormal Wavelet scaling function coefficient calculation (filter design)

I stumbled upon an equation system as shown in the image below while designing an orthonormal wavelet filter. I tried solving the equation (5.63,5.64,5.65 => 5.66) but no avail. I'm not sure if there'...
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0answers
103 views

High error due to resample function in MATLAB

I am working on training the output of the wavelet transform of a signal using a neural network in MATLAB. So I decided to use 3 layer ...
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0answers
442 views

Are discrete wavelet transform based statistical features invariant to rotation/translation/scale?

I'm reading a paper where image classification is done. Their approach is to use the discrete wavelet transform with bi-orthogonal wavelets of degree 3.5 and decomposition of level 3 on images. Based ...
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2answers
137 views

Why is successive decomposition of a signal performed only on low pass component?

The question says it all. In typical (wavelet-like) decomposition of a signal, why is only the low pass component chosen for successive decomposition ?
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1answer
2k views

What does “real time” signal processing mean?

I thought this was supposed to be an obvious question, until I finally set up my real time system. So basically I have a transmitter that sends 128 samples/second to a receiver. The transmitted ...
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1answer
2k views

Why use Wavelet Denosing instead of Band pass Filtering

What is the important advantage of adopting a wavelet based denosing scheme such as SURE, SUREshrink, etc. than using approaches involving low pass, high pass, band pass, band reject filter for signal ...
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0answers
72 views

What is the difference between Time-Frequency Represenation and TF Decomposition

I'm asking as I'm looking at Wavelet transforms, and I see that it is possible to have a TF decomposition or a representation of the signal. Looking for example at the code here we can see that the ...
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1answer
521 views

Wavelets: How does the admissibility condition imply this $\Psi(0)=0$

I'm reading through some material on wavelet and I'm finding it difficult to see why the following is true. Let $\Psi(\omega)$ is the Fourier transform of the mother wavelet $\psi(t)$ $$\int_{-\...
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1answer
2k views

Matlab stores all level of Wavelet's Approximation & Details in a single Row

I'd like to ask when we apply Wavelet transform on 1-D Signal in Matlab it simply stores both Approximations and Details into a single row which is quite annoying for me, have a look, Where, X = ...
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3answers
664 views

FIR / IIR and Wavelets

I am a self-learner of DSP by reading various books. I have accomplished basic understanding of Signals - CT and DT and a few transforms. I recently started to learn FIR / IIR Filters. The part that ...
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1answer
94 views

What are the settings of Daubechies and Complex Gaussian are called?

Hello What are the numbers of Daubechies and Complex Gaussian are called? I dont know what to call db4 or cgau8.
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1answer
320 views

time frequency localization using wavelet transform

I am currently doing analysis on Photoplethysmograph (PPG) data and I want to know the frequency (heart rate) at every time point so a windowed FFT might not be the best option. I am looking at ...
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2answers
1k views

Wavelet packet analysis, Sampling rate, Decomposition level

I am running Wavelet packet analysis for a 1-D signal. I want to estimate dominate frequencies in the original signal. Imagine I have following signal: ...
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2answers
2k views

Denosing signal using soft and hard thresholding

Let us consider following code: fs=100; N=1000; t=0:1/fs:N-1; y=10*sin(2*pi*100*t)+0.5*randn(size(t)); plot(y) plot(t,y) I have applied following threshold ...
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1answer
384 views

Does modified Morlet wavelet function satisfy the admissibility condition?

Does modified Morlet wavelet function satisfy the admissibility condition ? Do you have any reference for the answer please. Thanks.
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1answer
127 views

What are some ways to detect the fundamental frequency in a signal using without using FFT?

I am trying to estimate the fundamental frequency in a signal to corroborate the result which I have got by FPGA implementation of an FFT algorithm. Hence, could someone give me some idea how to do so?...
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1answer
952 views

How do you change pitch with wavelet transforms in MATLAB?

I'm trying to increase the pitch of a wav file using MATLAB. (I don't expect it to sound very good, but I'm trying to figure out how wavelets in MATLAB work.) Here's what I'm doing: ...
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1answer
3k views

Discrete (Inverse) Haar (2D) transform implementations

I am interested in implementations of the Haar transform, and its inverse, such that when composed always result in the identity operation. My inputs are discrete ordinals within a given range - and ...
3
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1answer
180 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
147 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
6k 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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1answer
222 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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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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0answers
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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0answers
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
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
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
1k views

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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0answers
33 views

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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1answer
312 views

Trying to understand WAVELET TRANSFORM Frequncy-Time diagram

I am reading The Wavelet Tutorial Part III MULTIRESOLUTION ANALYSIS & THE CONTINUOUS WAVELET TRANSFORM by Robi Polikar The author explains about the following fig and says; Note that ...
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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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2answers
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 ...