Signal Processing Stack Exchange
Signal Processing Stack Exchange

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1500 questions
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4 answers

What is the physical interpretation of Lowpass/Highpass filtering?

In Image/Signal processing context we have seen/we know that if there are say 4 samples and if we take an average of those 4 samples, then we say that the result sample is a low pass filtered output sample. This is very relevant in Image processing…
goldenmean
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3 answers

Contours matching - finding contours displacement

I found contours on two images with same object and I want to find displacement and rotation of this object. I've tried with rotated bounding boxes of this contours and then its angles and center points but rotations of bounding boxes don't tell…
krzych
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Is there any practical application for performing a double Fourier transform? ...or an inverse Fourier transform on a time-domain input?

In mathematics you can take the double derivative, or double integral of a function. There are many cases where performing a double derivative models a practical real-world situation, like finding the acceleration of an object. Since the Fourier…
tjwrona
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2 answers

Add odd/even harmonics to signal?

How do I add odd or even harmonics to a floating point signal? Do I have to use tanh or sin? What I'm trying to do is achieve some very simple distortion effects, but I'm having a hard time finding exact references. What I'd like is something…
Carlos Barbosa
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17
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2 answers

Detection of a Circle in Noisy Image Data

I have an image that looks like the one below: I'm trying to find the radius (or diameter) of the circle. I have tried using circular Hough transform (via matlab's imfindcircles(bw,[rmin rmax],'ObjectPolarity','bright')) , and by fitting to a…
bla
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5 answers

What factors should I consider when choosing an IIR filter realization?

IIR filters may be implemented as direct form 1 or 2. But how do you decide which form to use? What are the pros and cons of each?
anasimtiaz
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17
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5 answers

Scale and Rotation invariant feature descriptors

Can you list some scale and rotational invariant feature descriptors for use in feature detection. The application is for the detection of cars and humans in video captured by a UAV, using a multi-class classifier. So far I have been looking at SIFT…
Jono Brogan
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17
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4 answers

People detection from above

I am trying to find some method to detect people using only one camera 3 meters above the ground. This is a frame returned by camera: UPDATE: Video test -> http://dl.dropbox.com/u/5576334/top_head_shadow.avi In order to do that, first I understand…
emepetres
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1 answer

How to estimate and compensate for doppler shift in wireless signals?

I was wondering what good method(s) exist for the estimation (and subsequent compensation) of doppler shift for transmitted signals, be they acoustic or RF, in the context of comms. The question: Specifically, if the degree of doppler shift is…
Spacey
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Why is the difference of gaussians scale space scale invariant?

I'll use the Scale-invariant feature transform algorithm as an example here. SIFT creates a scale space based on scaled gaussian filtering of an image, and then computes the difference of gaussians to detect potential interest points. These points…
water
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2 answers

Is a Kalman filter suitable to filter projected points positions, given Euler angles of the capturing device?

My system is the following. I use the camera of a mobile device to track an object. From this tracking, I get four 3D points that I project on the screen, to get four 2D points. These 8 values are kinda noisy, due to the detection, so I want to…
Stéphane Péchard
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17
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Why real part of FFT converts image into rotation + original?

I have read this image: taken its FFT (2D) and then Inverse FFT to get exactly the image back. Code is provided for reference: imfft = fft2(photographer); im = uint8(ifft2(imfft)); imshow(im); %Output is same image But when I change the fourier…
Failed Scientist
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Wiener Filter for Image Noise Reduction (Image Denoising)

I'm trying to get my head round the operation of the Wiener filter for the purpose of image noise reduction. In my case I'll have used another noise reduction filter first and will then use the result of this as an approximation of the noise…
trican
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17
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How do I determine whether I have pattern-free noise?

For microscopy, we're frequently testing cameras. Since my applications involve very low signal-to-noise ratio, it becomes important that the noise is free of correlations and patterns, because local correlation is all that really distinguishes…
Jonas
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3 answers

Is ICA appropriate for separating mixed signals when all source signals are NOT detectable at all sensors?

A generic implementation of ICA for the separation of a mixture of $N$ signals into their $M$ constituent components requires that the signals be assumed to be a linear instantaneous mixture of the sources. Every description of ICA that I have come…
Laura
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