Questions tagged [dwt]

DWT denotes discrete wavelet transforms, instances of continuous wavelet transforms that admit a discrete sampling.

18 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
3
votes
1answer
37 views

At what stage do we compute the approximations and details while performing a DWT?

$$ \int_{-\infty}^{+\infty}{f(t)\psi_{j,k}^\ast(t)dt}\ \textrm{with}\ \psi_{j,k}(t)\ =\ a_0^{-j/2}\psi(a_0^{-j}t\ -\ b_0k) $$ If this is the expression for the wavelet transform, how does this lead to ...
1
vote
0answers
26 views

Best way to measure effectiveness of discrete wavelet denoising?

I am using matlab wavelet toolbox to denoise physiological signals, I am plotting the denoised signal on top of the original noisy signal and making sure spikes were not removed as a measure of ...
1
vote
1answer
33 views

Lifting scheme versus filter banks

I am having some trouble understanding the intuitive connection between the two. I worked through all the theory and learned that Sweldens showed how to derive lifting steps when having admissible ...
1
vote
1answer
65 views

Time location of the DWT detail coefficients using MATLAB

When performing the Discrete Wavelet Transform in MATLAB using the command DWT or WAVEDEC, what it the exact time or pseudo-time location of the DWT coefficients? At each level the time series is ...
1
vote
0answers
37 views

DWT vs. FFT for BPM detection

A BPM detection with FFT has been already highlighted on this site. Would DWT do the job as well? I've tried a Python script using DWT but it seems that the output is wrong, that is for the first 10 ...
1
vote
0answers
153 views

Aliasing from downsampling and Nyquist

In a book Conceptual Wavelets in Digital Signal Processing by Lee Fugal 2009 on page 246 the author talks about aliasing present in DWT subbands due to downsampling by 2 and states: Recall from DSP ...
1
vote
0answers
92 views

Discrete Wavelet Transform: Specifics of Filter Bank

So I have been given to understand that the discrete wavelet transform is able to provide both time and frequency resolution in ways that classic Fourier and even short time Fourier cannot. By ...
1
vote
0answers
42 views

What are the best suitable type of image moments (Hu, Zernike etc.) that can be applied on an Image after DCT/DWT?

I want to perform a block by block comparison by using overlapping blocks and their respective image moments. Can anybody suggest for type of image moment suited for blocks of DCT/DWT of that image. ...
1
vote
0answers
12 views

why double desity DWT use two HPF?

The double-density DWT is an improvement upon the critically sampled DWT with important additional properties: It employs one scaling function and two distinct wavelets, which are designed to be ...
1
vote
1answer
226 views

2D DWT computation order

In 2D the discrete wavelet transform (DWT) of an image using lifting based 5/3 filter, if I perform a row-wise operation first then perform column-wise operation then I will get 4 sub-band LL, LH and ...
1
vote
0answers
45 views

DWT initialization from nonuniform samples

Let $D\subset\mathbb R$ be compact, let $f:\mathbb R\to\mathbb R$ be a contintinuous function with support $D$. Let $\phi(x)$ be a well-defined scaling function, in the sense that it generates a ...
0
votes
0answers
8 views

How well can discrete wavelet packet transform reduce noises that are similar to the input signal in the same frequency band?

If I had 50Hz noise coming from power line, and signals in the same frequency range (EEG for example 0.1Hz to 100Hz). If my sampling frequency is 30kHz but I downsample my signal to 937kHz and use the ...
0
votes
1answer
27 views

DWT on short signals

I have signals with a very short rate of ~100e-6 seconds, sampled at 10MHz,so about 1k samples. I am wondering, is there a practical limit to the usefulness of time-frequency methods concerning a ...
0
votes
1answer
347 views

Discrete Wavelet Transform (DWT) Filter Bank

I have some stumbling block in my thesis writing. Do we use the same filter pair while implementing DWT filter bank with downsampling of the filter output, or filters do change also from level to ...
0
votes
0answers
43 views

What are the constraints in design of discrete orthogonal wavelets?

Can anyone point me to literature that explains a quote from here : Why is a wavelet transform implemented as a filter bank? So not all wavelets can be implemeted perfectly (invertible) with ...
0
votes
1answer
549 views

Wavelet transform of a spatial convolution

Does anyone know if there exist a kind of convolution theorem for the discrete wavelet transform (decimated or undecimated)? In other words can I find a simple form of $W\left[ \int f(t) g(x-t) \, ...
0
votes
1answer
365 views

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 ...
-1
votes
1answer
456 views

DWT versus band-pass filter

Which technique gives better result in extracting a band from a signal, let's say the alpha band (8-13 Hz): using a band-pass-filter or a DWT (Discrete Wavelet Transformation)? P.S.: I am working in ...