# 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.

445 questions
Filter by
Sorted by
Tagged with
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 ...
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 ...
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 ...
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 ...
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: ...
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 ...
1k views

### denosing using soft thresholding or hard thresholding in matlab

let us consider following code ...
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 ...
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 ...
445 views

### Denoise images with wavelets

I try to understand what following algorithm from this gimp plugin does to denoise an image: ...
61 views

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: ...
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: ...
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 ...
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 ...
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 ...
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, ...
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 ...
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'...
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 ...
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 ...
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 ?
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 ...
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 ...
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 ...
521 views

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_{-\... 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 = ... 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 ... 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. 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 ... 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: ... 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 ... 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. 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?... 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: ... 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 ... 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/... 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)... 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 ... 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 ... 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 ... 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 ... 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. ... 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? 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 ... 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 ... 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 ... 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 ... 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....
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 ...