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1500 questions
9
votes
2 answers
Noise reduction from very noisy audio
I am trying to write an algorithm that would automatically segment a piece of audio with bird calls recordings. My input data are 1 minute-long wave files and on the output I would like to get separate calls for further analysis. Problem is that…
Lukasz Tracewski
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9
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3 answers
Why Is Bi Quadratic Interpolation for Image Resampling / Interpolation Rarely Done?
Related question: What are the practically relevant differences between various image resampling methods?
Bilinear and bicubic interpolation for image resampling seem to be fairly common, but biquadratic is in my experience rarely heard of. To be…
Sami Liedes
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9
votes
1 answer
Remove artifact from space probe image
This is a photo of our homeworld, taken by the Juno spacecraft recently, sling-shotting on its way to Jupiter. What it gained in speed, we lost in ours, however thankfully we will not be falling into the sun.
I think the South American continent…
TheGrapeBeyond
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9
votes
1 answer
FFT of image data: "mirroring" to avoid boundary effects
I load and display an image of some rice in Matlab:
g = imread('rice.png');
imshow(g);
I take the FFT of this image and shift it:
G = fft2(g);
imshow(log(abs(fftshift(G)) + 1), []);
If I place a x and y axis trough the center of the image; I…
Andy
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9
votes
1 answer
Applying FIR filter to data with different sample rates
I have a filter design, and it filters over a 1-2 kHz range.
What should I do if I want to apply it to data with a different sample rate than the one for which it was designed?
Let's say it consists of Bessel and Chebyshev filters. How do I find a…
zetah
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9
votes
2 answers
Find a specific line in a picture
I want to find the line between color blue and color gray in the following picture:
More exactly, the end points of that line.
Is the Hough transform a choice? If yes how should I set up the picture before using Hough?
Any way of solving this would…
andreea lapusneanu
9
votes
1 answer
Why is anisotropic diffusion useful in image processing?
I am working on anisotropic diffusion and the two coefficients proposed by Perona & Malik.
I wanted to know what is the use of diffusion in image processing? Why is anisotropic diffusion important and in which fields is it commonly used?
vini
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9
votes
1 answer
Ideas on Matrix Factorization / Transformations for $ {L}_{1} $ Minimization
I am starting with a typical $\ell_1$ basis pursuit problem:
$$
\min_{\mathbf{x}} \Vert \mathbf{x} \Vert_1 \quad \mathrm{s.t.} \quad \Vert \mathbf{ERx} - \mathbf{y} \Vert_2 \leq \epsilon,
$$
where $\mathbf{R}\in\mathbb{C}^{M \times P}$, and…
AnonSubmitter85
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9
votes
1 answer
Question on covariance matrix of 2 spatial signals
Every time I think I have understood the covariance matrix, someone else comes up wih a different formulation.
I am currently reading this paper:
J. Benesty, "Adaptive eigenvalue decomposition algorithm for passive acoustic source localization", J.…
Spacey
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9
votes
3 answers
Is Ideal LPF BIBO unstable?
In one of other discussions : How to find frequency response, stability, and causality of a linear system?
I found a comment which was quite strong and definitely caught my attention.
An ideal low-pass filter is an example of a system that is not…
Dipan Mehta
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9
votes
1 answer
Frequency Modulation Synthesis Algorithm
Based on what I read, I've made an algorithm for FM sound synthesis. I'm not sure if I did it right. When creating a software synth instrument a function is used to generate an oscillator and a modulator can be used to module the frequency of this…
Matthew Mitchell
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9
votes
5 answers
Why more poles than zeroes?
I read that an "improper system" "has more zeros than poles; it is not causal, cannot be implemented, has a strictly proper inverse and has infinite high-frequency gain."
Does causality fail due to instant signal change? I try to make up a…
Val
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9
votes
2 answers
Spectral Entropy Calculation in MATLAB
How do I calculate the Spectral Entropy of a signal in MATLAB ? I know the basic steps but it would be nice if someone can help,
Calculate the power spectrum of the signal using FFT command in MATLAB.
Calculate the Power Spectral Density using the…
RRelan
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9
votes
1 answer
What is the story behind the story about SIFT descriptor?
The following is from Lowe 2004 paper ( http://www.cs.ubc.ca/~lowe/papers/ijcv04.pdf ).
One obvious approach would be to sample the local image intensities around the keypoint at the appropriate scale, and to match these using a normalized…
jakeoung
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9
votes
1 answer
Discrete Fourier transform - finding the fundamental quickly?
First, I appologize because I'm a software developper and it's been a very long time I didn't dive into pure mathematics, so my question might seem dumb. I hope not.
The context is pitch recognition in music.
If you take a musical note, and apply a…
Dinaiz
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