# All Questions

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### Does the enlarged photo benefit from shrinking it?

Take a look at the following diagrams: The original picture: The upscaled (2x, bilinear) picture: In both cases the first item in first row is the input image. There is it's 2d fft next to it. ...
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### What's the use case and explanation of frequency-domain subsampling?

In my solution to a certain problem I use subsampling in the frequency domain. Amazingly, it produces good results. Is it really that awkward to see subsampling in frequency domain? What the ...
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### Kalman filter for velocity estimation from acceleration and displacement: constant-acceleration assumption

I have implemented a Kalman filter to estimate the velocity knowing the acceleration and the positon measurements as explained in this Q/A: Estimating velocity from known position and acceleration ...
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### homography matrix problem

i have mini project to do about homography , but i am really a beginner in matlab . i have calculated the homography matrix easily by taking a set pixels from both images but the problem is how to ...
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### Inferring space domain signal from 2D DFT

By just looking at the 2D Fourier Transform of a signal, can it every be known precisely which values in the space domain are zero?
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### Upscaling detection approach

I'm trying to implement a solution that would, to some extent, evaluate a picture telling what are the chances that it was upscaled from the smaller image. My approach is as follows: Take a picture ...
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### Circle detection opencv

I Would like an explanation of the parameters for opencv's HoughCircles function. I'm new to image processing in general and I have recently started using opencv. ...
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### How does sampling and subsequent resampling affect aliased harmonics?

If I sample a signal with a harmonic higher than half my sample frequency I can predict the aliased frequency easily as $$|F_h-kF_s|$$ But what if after sampling the signal, I re-sample at a lower ...
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### What preprocessing technique can help me to filter the background text noises using matlab…the image is shown below?

Can anyone help me to improve the degradation of the following image....i am working on OCR system in Amharic language and what is the best image filtering technique that can help me to separate ...
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### How to determine stopband of discrete Gaussian, stdev sigma, support N

I would like to analyse a gaussian smoothing kernel with a set standard deviation and support (let's say, in MATLAB, fspecial('gaussian', [5 1], 1.3) so sigma is 1.3 and support is 5) in the DTFT ...
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### Is image reconstruction possible using its magnitude only?

Let us take any image like Lena or cameraman. I know that when Fourier transform is applied on image,spatially global features like amplitude and phase are obtained locally. My question is whether it ...
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### How to programatically perform image segmentation in real-time

I am currently trying to segment ultrasound images of blood vessels (video frames), such as the one directly below. Using a simple binary filter on the saturation channel (code below), I can get a ...
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### Correction of signal after High-pass RC-filter

I have one question about digital correction of signal after RC filter which is high-pass. Let me explain detail. I have one simple signal conditioner. It has RC filter on the signal input with ...
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### DFT and Inverse DFT in Image Processing

I have implemented DFT from this link. 1) Tried taking dft for the three Channels(R, G and B) and reconstructed the original image by taking inverse dft for all three channels and merged them ...
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### I saw this question on one of the sites related to DFT

The analog signal x(t) is band-limited to 40 Hz. Suppose the signal is sampled at the rate of 100 samples per second and that at this rate 200 samples are collected. Then 200 zeros are appended to the ...
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### Multi-image denoising

I have two signals Sa and Sb, both affected by the same noise. I don't know how much noise is mixed into each one, and the signal+noise is transformed using some (unknown) nonlinear function before I ...
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### Determining the point in a temporal signal when a periodic behavior begins to occur

I'm a newcomer to digital signal processing, so I'm looking for some general advice and direction on this problem I have. I have a signal like that shown below. Starting around x=40000, you can see a ...
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### Significance of Lambda in Basis pursuit

In basis Pursuit,l1 minimization is done to perform compressed sensing.In the literature there is a lamba parameter used as a regulizer. What is its significance?