Signal Processing Stack Exchange
Signal Processing Stack Exchange

Most Popular

more tags
1500 questions
29
votes
4 answers

Gaussian Blur - Standard Deviation, Radius and Kernel Size

I've implemented a gaussian blur fragment shader in GLSL. I understand the main concepts behind all of it: convolution, separation of x and y using linearity, multiple passes to increase radius... I still have a few questions though: What's the…
LodeRunner
  • 393
  • 1
  • 3
  • 5
28
votes
4 answers

Find the stomata in a plant microscopy image

Here is a question for image processing experts. I am working on a difficult computer vision problem. The task is to count the stomata (marked below) in DIC microscopy images. These images are resistant to most superficial image processing…
Matt M.
  • 1,078
  • 7
  • 12
28
votes
8 answers

Are Computer Stereo Vision techniques appropriate for sub-millimetre measurements?

I have a project where I would like to image an object and be able to derive the heights of features in this image to sub-millimetre precision (exactly how precise is still yet to be determined, but let's say 100ths of a millimetre for now). I have…
Stephen
  • 731
  • 8
  • 14
28
votes
1 answer

Mathematics of Harris corner point detection

This is the mathematical expression for Harris corner detection: But I have the following doubts: What is the physical significance of $u$ and $v$? Many references say it is the magnitude by which the window $w$ shifted. So how much is the window…
rotating_image
  • 601
  • 1
  • 9
  • 16
28
votes
2 answers

Overlap-Add versus Overlap-Save

What differences or other criteria can be used to help decide between using overlap-add and overlap-save for filtering? Both overlap-add and overlap-save are described as algorithms for doing FFT based fast convolution of data streams with FIR…
hotpaw2
  • 35,346
  • 9
  • 47
  • 90
27
votes
1 answer

What is the difference between PSD and squared magnitude of frequency spectrum?

The power spectrum of a signal can be calculated by taking the magnitude squared of its Fourier transform. Being an audio person, the signal of interest for me would be a time series. How does this representation differ from a PSD (power spectral…
learnvst
  • 1,513
  • 2
  • 17
  • 25
27
votes
6 answers

Calculating the PDF of a waveform from its samples

A while ago I was trying different ways to draw digital waveforms, and one of the things I tried was, instead of the standard silhouette of the amplitude envelope, to display it more like an oscilloscope. This is what a sine and square wave look…
endolith
  • 15,759
  • 8
  • 67
  • 118
27
votes
5 answers

When is aliasing a good thing?

In Hamming's book, The Art of Doing Science and Engineering, he relates the following story: A group at Naval Postgraduate School was modulating a very high frequency signal down to where they could afford to sample, according to the sampling…
datageist
  • 4,897
  • 4
  • 32
  • 53
26
votes
1 answer

What are the practically relevant differences between various image resampling methods?

Mathematica's ImageResize function supports many resampling methods. Not being familiar with this area, beyond nearest neighbour, bilinear, biquadratic and bicubic (which are obvious from the name), I am lost. Can you point me to some source that…
Szabolcs
  • 365
  • 1
  • 3
  • 12
26
votes
4 answers

What effect does a delay in the time domain have in the frequency domain?

If I have a signal that is time limited, say a sinusoid that only lasts for $T$ seconds, and I take the FFT of that signal, I see the frequency response. In the example this would be a spike at the sinusoid's main frequency. Now, say I take that…
gallamine
  • 693
  • 1
  • 5
  • 10
26
votes
4 answers

FIR Filter Design: Window vs Parks McClellan and Least Squares

Are there any advantages to use a window approach over Parks-McClellan (further abbreviated here as PMcC) or Least Squares algorithms for FIR filter design of a low pass filter? Assume with today's computational power that the complexity of the…
Dan Boschen
  • 50,942
  • 2
  • 57
  • 135
26
votes
2 answers

Stationary vs non-stationary signals?

There are nice technical definitions in textbooks and wikipedia, but I'm having a hard time understanding what differentiates stationary and non-stationary signals in practice? Which of the following discrete signals are stationary? why?: white…
matousc
  • 667
  • 1
  • 6
  • 16
26
votes
3 answers

Intuitive explanation of cross-correlation in frequency domain

According to the cross-correlation theorem : the cross-correlation between two signals is equal to the product of fourier transform of one signal multiplied by complex conjugate of fourier transform of another signal. After doing this, when we take…
silver surfer
  • 523
  • 2
  • 5
  • 11
26
votes
3 answers

Fastest Algorithm for Distance Transform

I am looking for the fastest available algorithm for distance transform. According to Image Processing Learning Resources - HIPR 2 (HYPERMEDIA IMAGE PROCESSING REFERENCE) - Morphology - Distance Transform: The distance transform can be calculated…
Karl
  • 837
  • 1
  • 9
  • 13
26
votes
3 answers

How to find tennis courts in aerial imagery

I'm interested in finding all tennis courts (and other similar well defined features like basketball courts) in my county, and I have aerial imagery of good (but varying) resolution, but I'm not sure of the best way to find them. Here are two…
joshdoe
  • 363
  • 2
  • 6
1 2 3
…
99 100