Signal Processing Stack Exchange
Signal Processing Stack Exchange

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1500 questions
38
votes
5 answers

Why are Gaussian filters used as low pass filters in image processing?

In 1d signal processing, many types of low pass filters are used. Gaussian filters are almost never used, though. Why are they so popular in image processing applications? Are these filters a result of optimizing any criterion or are just ad hoc…
nimrodm
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37
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2 answers

Filter order vs number of taps vs number of coefficients

I'm learning DSP slowly and trying to wrap my head around some terminology: Question 1: Suppose I have the following filter difference equation: $$y[n] = 2 x[n] + 4 x[n-2] + 6 x[n-3] + 8 x[n-4]$$ There are 4 coefficients on the right-hand side.…
stackoverflowuser2010
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36
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6 answers

Flipping the impulse response in convolution

During convolution on a signal, why do we need to flip the impulse response during the process?
winuall
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36
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5 answers

What is the true meaning of a minimum phase system?

What is the true meaning of a minimum phase system? Reading the Wikipedia article and Oppenheim is some help, in that, we understand that for an LTI system, minimum phase means the inverse is causal and stable. (So that means zeros and poles are…
TheGrapeBeyond
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36
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9 answers

Is there an algorithm for finding a frequency without DFT or FFT?

I was looking in the Android app store for a guitar tuner. I found a tuner app that claimed it was faster than other apps. It claimed it could find the frequency without using the DFT (I wish I still had the URL to this specification). I have never…
Slamice
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35
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5 answers

What factors should I consider in choosing an edge detection algorithm?

I've learned about a number of edge detection algorithms, including algorithms like Sobel, Laplacian, and Canny methods. It seems to me the most popular edge detector is a Canny edge detector, but is there cases where this isn't the optimal…
PearsonArtPhoto
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35
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7 answers

Finding squares in Image

I need to find the squares in an image using OpenCV (no problem in matlab or any other, generally what i expect are some ideas). Consider the test image below : I need to find those coloured squares in above image accurately (not the white long…
Abid Rahman K
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34
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5 answers

How to create a sine wave generator that can smoothly transition between frequencies

I am able to write a basic sine wave generator for audio, but I want it to be able to smoothly transition from one frequency to another. If I just stop generating one frequency and immediately switch to another there will be a discontinuity in the…
Mark Heath
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34
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5 answers

"Complex sampling" can break Nyquist?

I have heard anecdotaly that sampling complex signals need not follow Nyquist sampling rates but can actually be gotten away with half Nyquist sampling rates. I am wondering if there is any truth to this? From Nyquist, we know that to unambiguously…
Spacey
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34
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6 answers

Why is a linear phase important?

If symmetry conditions are met, FIR filters have a linear phase. This is not true for IIR filters. However, for what applications is it bad to apply filters that do not have this property and what would be the negative effect?
The Pheromone Kid
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34
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3 answers

Picking the correct filter for accelerometer data

I am fairly new to DSP, and have done some research on possible filters for smoothing accelerometer data in python. An example of the type of data Ill be experiencing can be seen in the following image: Essentially, I am looking for advice as to…
Michael M
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34
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5 answers

What Are the Best Algorithms for Document Image Thresholding (Example Inside)?

I'm trying to implement various binarization algorithms to the image shown: Here's the code: clc; clear; x=imread('n2.jpg'); %load original image % Now we resize the images so that computational work becomes easier later onwards for…
mark
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33
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2 answers

What is the cut-off frequency of a moving average filter?

I need to design a moving average filter that has a cut-off frequency of 7.8 Hz. I have used moving average filters before, but as far as I'm aware, the only parameter that can be fed in is the number of points to be averaged... How can this relate…
CaptainProg
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33
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6 answers

Detecting Trail in Forest Images

Is anyone aware of any research/papers/software for identifying a trail (as a line or point-to-point curve) in an image of a forest scene (from the perspective of the camera standing somewhere along the trail)? I'm trying to find an algorithm that…
Cerin
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33
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4 answers

How to understand Kalman gain intuitively?

The Kalman filter algorithm works as follows Initialize $ \hat{\textbf{x}}_{0|0}$ and $\textbf{P}_{0|0}$. At each iteration $k=1,\dots,n$ Predict Predicted (a priori) state estimate $$ \hat{\textbf{x}}_{k|k-1} = …
Tim
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