Questions tagged [convolution]
Convolution is a mathematical operation on two functions f and g, producing a third function that is typically viewed as a modified version of one of the original functions.
22
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6answers
12k views
Flipping the impulse response in convolution
During convolution on a signal, why do we need to flip the impulse response during the process?
8
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10answers
29k views
Deconvolution of 1D Signals Blurred by Gaussian Kernel
I have convolved a random signal with a a Gaussian and added noise(poisson noise in this case) to generate a noisy signal . Now I would like to deconvolve this noisy signal to extract the original ...
44
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16answers
118k views
What is the physical meaning of the convolution of two signals?
If we convolve 2 signals we get a third signal. What does this third signal represent in relation to the input signals?
45
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4answers
40k views
What is the difference between convolution and cross-correlation?
I've found on multiple sites that convolution and cross-correlation are similar (including the tag wiki for convolution), but I didn't find anywhere how they differ.
What is the difference between ...
19
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1answer
5k views
How to circularly shift a signal by a fraction of a sample?
The shift theorem says:
Multiplying $x_n$ by a linear phase $e^{\frac{2\pi i}{N}n m}$ for some integer m corresponds to a circular shift of the output $X_k$: $X_k$ is replaced by $X_{k-m}$, where ...
7
votes
2answers
9k views
What is the difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat wavelet?
There are three techniques used in CV that seem very similar to each other, but with subtle differences:
Laplacian of Gaussian: $\nabla^2\left[g(x,y,t)\ast f(x,y)\right]$
Difference of Gaussians: $ \...
3
votes
1answer
2k views
1D Deconvolution with Gaussian Kernel (MATLAB)
Suppose that I know the output and the transfer functions of a system and I would like to calculate the input function using deconvolution.
To get a grasp of the idea I have created a simple ...
5
votes
1answer
181 views
Difference between convolving before/after discretizing LTI systems
Suppose I have transfer functions for two continuous causal linear-time invariant (LTI) systems:
$F_1(s)$ and $F_2(s)$.
Let $D\left\{\cdot\right\}$ denote the function that maps a transfer function ...
5
votes
2answers
5k views
Sampling theorem and Dirac comb
I am reading "The Scientist and Engineer's Guide to Digital Signal Processing" and trying to understand Figure 3.5 below which is about the sampling theorem and aliasing.
I do not understand the ...
0
votes
1answer
309 views
understanding discrete-time convolution in LTI systems
I'm trying to understand the discrete-time convolution for LTIs and its graphical representation. standard explanations (like: this one) start with the idea of decomposing an input signal $x[t]$ into ...
15
votes
1answer
35k views
Difference between correlation and convolution on an image?
Could you please clearly explain what is the difference between correlation and convolution that is done by a filter on an image?
I mean in terms of signal processing definition I know that ...
5
votes
1answer
11k views
How are two signals multiplied? And how is it different from convolving two signals?
Suppose that I have two signals $x[n] = \left\{2,4,1\right\}$ and $p[n] = \left\{5,1,8\right\}$ and I want to multiply them.
How do you do that?
How different is it from convolving two signals?
I ...
11
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1answer
1k views
How to find the convolution kernel in frequency domain?
I have a two vectors of spatial data (each about 2000 elements in length). One is a convolved version of the other. I am trying to determine the kernel that would produce such a convolution. I know ...
5
votes
2answers
3k views
Simulating analog filter using convolution or converting with fft
My task is simple; I want to simulate analog low-pass filtering of an input signal, using Python. Note that the input signal is an array of values, not an analytical function.
My first question is if ...
3
votes
3answers
1k views
Sweep signal + microphone-recorded signal => Impulse response
I played this signal A (a 20Hz to 20000Hz sinusoidal sweep in 10 seconds) with a studio monitor speaker in a big church, and I recorded the result B with good microphones.
The result is very reverb-...
2
votes
1answer
289 views
Convolution of $\sin(\omega t)$ and $\cos(\omega t)$?
If $x(t)=\sin(\frac{\pi t}{4})$ and $y(t)=\cos(\frac{\pi t}{4})$ then i need to find the Convolution $$z(t)=x(t) \circledast y(t)$$
So convolution will be
$$\begin{align}
z(t) &=\int_{-\infty}^{...
4
votes
1answer
315 views
Can two nonzero signals $x[n]$ and $y[n]$ give a zero convolution
Suppose $x[n]$ and $y[n]$ are two nonzero signals(i.e., $x[n] \neq 0$ for at least one value of n and similarly for $y[n]$).Can the convolution between $x[n]$ and $y[n]$ result in an identically zero ...
3
votes
1answer
958 views
Efficient FFT computation of a zero-padded vector
I don't think this question has a good answer but will ask nevertheless since it has been bothering me for a few days.
I am interested in computing as efficiently as possible the N-point FFT of a N/2 ...
2
votes
3answers
2k views
Get a N-FFT with two N/2-FFT already computed
After somme researchs on the web, I don't find the answer of my problem (or I don't understand it) and I hope this post will succeed.
I'm working on a real-time FFT convolution algorithm (C++) which ...
2
votes
3answers
2k views
Why unit impulse function is used to find impulse response of an LTI system?
Hello i am working in digital image restoration field, recently i have studied concept of convolution, i studied that to find the impulse response/point-spread function of an LTI system, an unit ...
1
vote
2answers
666 views
Fourier transform of a Fourier transform
I generate a Gaussian noise and then I filter it with a passband FIR Kaiser window filter. When I perform the Fourier transform of the output of the filter and plot its magnitude spectrum, it is ...
5
votes
1answer
3k views
When convolving two functions that are constants in a region and 0 everywhere else, where does the integration start?
Heads up, this is for homework. I never took a signals and systems course, so I'm behind on this stuff.
I want to compute the convolution of two rectangular regions. I know the standard equation ...
3
votes
1answer
401 views
2D deconvolution of recorded electron beam data
I'm currently working on a project that involves using an electron gun and it would be really nice to know the spot shape of the electrons coming out of the gun (the frequency of electrons at some x,y ...
3
votes
2answers
3k views
When should the sum of all elements of a gaussian kernel be zero?
I found an approximation of a 5x5 2D convolution kernel like this :
Here, the sum of the elements is zero and this one was used for Laplacian of Gaussian!
Another one here :
This one has all ...
2
votes
1answer
275 views
Filtering $ n \times n $ Images by Separable $ m \times m $ Filters. Computation Time for Filtering Using FFT, 2D Convolution and Two 1D Convolutions
Consider filtering square $n\times n$ images by square, separable $m\times m$ filters.
Give general equations for the computation time for the following approaches to this:
Filtering using FFT
2-D ...
2
votes
2answers
281 views
Need help understanding convolution indexing
Ok, this is leaving me increasingly frustrated. This builds on a previous question here but I am still not getting the indexing, although I learned from that question all the same.
Case 1: First ...
0
votes
3answers
1k views
Convolution and windowing using a buffer - how do I do overlap add?
I'm reading chunks of audio signal (1024 samples) using a buffer, applying a Hanning window, doing an FFT on it, then reading an Impulse Response, doing its FFT and then multiplying the two (...
0
votes
1answer
117 views
Using the flip-and-drag method to draw a convolution
So, we are asked to graphically convolve (using the flip-and-drag method) the following pair of signals: $$x_1(t) = \delta(t+1)-2\delta(t-1) \ \ \ \ \ \ \ \ \ \ \ \ \ x_2(t) = \begin{cases} -1-2t, &...
4
votes
1answer
3k views
How do real-time convolution plugins process audio so quickly
Okay, so in Logic Pro I can load up a Space Designer plugin (convolution reverb) with an impulse that's 9.1 seconds long, turn my mic on, and get real-time convolution reverb as the mic records ...
5
votes
2answers
4k views
Standard Deviation in Gaussian Blur
I have a function that performs gaussian blur on image for some specific $\sigma$ (the standard deviation).
It first computes kernel of size $\lceil 3\sigma \rceil$ and then performs convolution with ...
4
votes
1answer
301 views
Help Understanding Convolution Filter Formulation
I'm reading Computer Vision: Algorithms and Applications wich is available online as a PDF and on Chapter 3.2 page 111 it introduces convolution operators for images giving the formulation:
$g(i, j) =...
2
votes
4answers
2k views
A better explaination for 'there's no flipping of the impulse response' [closed]
I showed the question about flipping the impulse response to some math teachers and electrical engineers at an university. They read Dilip's answer and thought that it was hard to understand what ...
0
votes
1answer
3k views
Exponential average with time constant of slow, fast and impulse
I have been studying about exponential average. There are enough explanations about this at Internet, but they do not explain about the time constant.
I have one channel with a $T$ seconds time ...
6
votes
2answers
3k views
MOD-N Circular Convolution
How to find MOD-2 Circular convolution for the two sequences $h =[-1,3,-2,1]$ and $x = [1,-1,-2,1,3,2,1,2]$.
I know the answer is $7$ $0$ from matlab but I don't know how to find it graphicly or ...
4
votes
4answers
2k views
Deconvolution by Convolution
This is now a second time I am attempting to ask this very important but simple question here. What I want to know is can you do deconvolution by convolving a signal. It is often stated that, for ...
4
votes
1answer
1k views
Common Use Cases for 2D Non Separable Convolution Filters
In the image processing world, I've noticed that a lot of the popular convolution filters are separable. Here's a quick list of common separable filters:
Sobel
Gaussian blur
Box filter (all ones, for ...
4
votes
1answer
12k views
Get an input signal from LTI system output, find impulse response
I just study signal processing and I have some questions.
How to find impulse response $h[n]$ sequence of the system if I have
$x[n]$ and $y[n]$ (input and output) sequences? Hope there is a formula
...
2
votes
1answer
5k views
Deconvolution in Python
I'm trying to use and understand SciPy's deconvolve for a project I'm working on. I'm having some trouble understanding how to use it.
What I would like to do is to take two PMFs from discrete ...
2
votes
2answers
3k views
How to find the input if I have the impulse response and the output of a finite sequence?
I understand how to find the output from the input with an impulse response, but how can I go about finding the input if given the other two?
I have $y[n] = [-1, -1, 11, -3, 30, 28, 48]$ and $h[n] = [...
0
votes
1answer
235 views
Sharpen Defocused Image (Deconvolution / Image Restoration)
Using OCR, I want to extract text from product packages using Google Glass. However, because of the fixed focus of the camera the package pictures are blurred. Is there a way to sharpen the image? ...
0
votes
1answer
1k views
Generate the Matrix Form of 2D Convolution Kernel
We know that a convolution can be replaced by a multiplication with a toeplitz circulant matrix. Meaning, assume I have convolution kernel $h$ and matrix $I$ (of size $m \times m$ for example), then ...
-3
votes
1answer
471 views
Ideal BandPass Filter
Let suppose
x(t)=$\sum\limits_{k=-∞}^∞ R(t-kT)$
$R(t) = \begin{cases}1 &[0,2T] \\ 0 & \text{otherwise} \end{cases}$
x(t) is the input to an ideal bandpass filter with $\text{BandWidth} = \...
6
votes
2answers
880 views
Question about convolution in time and frequency domain
My question is about the number of data points when doing a convolution (or correlation) in the the time or frequency domain. let's say we have two signals, $a(t)$ and $b(t)$ each of length $16$. When ...
3
votes
1answer
351 views
Fourier transform of Kernel Density estimate: convolution theorem?
I am reading this paper about density estimation (Appendix A), where the authors apply a Fourier transform to the estimated probability density (the $X_j$ are a sample of $N$ data points drawn ...
3
votes
2answers
80 views
What is the relation between kernel functions, kernels used in convolution and null spaces of a matrix?
I have recently started learning about machine learning and have come across kernels and null spaces. I understand that null space is the set of all vectors that satisfy the equation A.v = 0 (Where A ...
3
votes
1answer
6k views
Difference between linear convolution and circular convolution for a kernel
If I understood correctly (and this page should confirm: http://www.cs.ioc.ee/~khoros2/linear/convolution-teo/front-page.html)
if I convolve linearly (the usual point-to-point multiplication and ...
3
votes
1answer
207 views
Is it possible to simplify the convolution integral if the functions are non-zero in disjoint areas? [duplicate]
Possible Duplicate:
When convolving two functions that are constants in a region and 0 everywhere else, where does the integration start?
I have a function $f(x,y)$ and $h(x,y)$. $f(x,y)$ has a ...
2
votes
2answers
392 views
Convolution in frequency domain
Simple math question. The convolution theorem states that multiplication in time domain is equal to convolution in frequency domain and vice versa. There is a condition that the signal has to be ...
2
votes
1answer
320 views
Exponential decaying step response in LTI System
I'm attempting to better understand the relationship between step responses, impulse responses, and convolutions. Say that I have a system where if I apply a constant input, my output decays from a ...
2
votes
2answers
1k views
Difference between convolution and multiplication of freq. response and freq. spectrum
Suppose I have impulse response like [1/25,2/25,3/25,4/25,5/25,4/25,3/25,2/25,1/25].
I did convolution with 600 samples of test signal (it seems that I did some filtering).
Then I calculated the ...
