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1500 questions
18
votes
2 answers
A (Clear) Line Between Computer Vision and Image Processing
I have been working in and learning about both Computer vision and Image processing for a few years now, and I believe that I am not a complete beginner any more.
Still, after all these years, it is hard for me to tell for any particular part of my…
penelope
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18
votes
4 answers
Counting the number of groups of 1s in a boolean map of numpy.array
I am right now dealing with some image processing in Python via PIL (Python Image Library). My main aim is counting the number of colored cells in an immunohistochemistry image. I know that there are relevant programs, libraries, functions and…
Ibrahim C. Kurt
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18
votes
2 answers
Downsampling an image by an integer factor
When downsampling an image by an integer factor $n$, the obvious method is to set the pixels of the output image to the average of the corresponding $n \times n$ blocks in the input image.
I remember vaguely having read somewhere that this method is…
Styg Oldenbaum
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18
votes
4 answers
Feature extraction for sound classification
I'm trying to extract features from a sound file and classify the sound as belonging to a particular category (eg : dog bark, vehicle engine e.t.c). I'd like some clarity on the following things :
1) Is this doable at all? There are programs that…
Kevin Martin Jose
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18
votes
2 answers
How do I manually plot the frequency response of a bandpass Butterworth filter in MATLAB without freqz function?
I have code like below that applies a bandpass filter onto a signal. I am quite a noob at DSP and I want to understand what is going on behind the scenes before I proceed.
To do this, I want to know how to plot the frequency response of the filter…
William
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18
votes
3 answers
A good textbook for designing signal filters
Since a couple of months ago I started being actively involved in the area of control of dynamical systems.
In most cases, designing a controller for a given dynamic system will require the employment of digital signal processing techniques,…
fpe
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18
votes
3 answers
When to use the DTFT vs the DFT (and their inverses) in analysis?
In many of my readings, whenever some author speaks about working in the frequency (transform) domain (of a digital signal), they often times take the DFT, or the DTFT, (and of course their corresponding inverses). Different authors will tend to…
TheGrapeBeyond
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18
votes
3 answers
What are the advantages, if any, of derivative sampling?
In Five short stories about the cardinal series $[1]$, the author makes the following comment:
Interestingly enough, Shannon goes on to mention that other sets of
data can also be used to determine the band-limited signal--for
example, the…
datageist
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17
votes
3 answers
How do the motion vectors work in predictive coding for MPEG?
In MPEG, there is a process where an image is broken up into macroblocks and a motion vector is computed for each of those macro blocks. You then transmit these vectors, along with the prediction errors, to reconstruct the next image in the video…
Wallet
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17
votes
1 answer
Digital filter design basic principles (IIR/FIR)
Although I have a solid experience in designing audio engines and such, I am fairly new to the realm of Digital Filter Design, particularly IIR and FIR filters. In other words, I'm trying to learn as much as I can on how to design filters and derive…
bitwise
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17
votes
2 answers
Could a DCT be used for an audio magnitude spectrum rather than DFT?
From what I understand, the DCT has half the bin size as a DFT of the same size N. The DFT also includes phase information, but often this is not needed when only the magnitude spectrum is desired.
Could the DCT be used to provide a magnitude…
Jacob
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17
votes
4 answers
How to compute dBFS?
I asked myself how to compute dBFS (dB full scale) from a value of sample between 1 and -1?
and in general?
JustGoscha
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17
votes
5 answers
FFT of sine wave not coming as expected i.e single point
The cyan plot is a spectrum of 50 Hz, and the magenta one is a 50.1 Hz sine wave (having amplitude 0.7). Both are sampled at 1024 samples/s. I performed a 1024 point FFT to get this spectrum.
Why is only the 50Hz spectrum a single value? Why does…
gpuguy
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17
votes
2 answers
PSD (Power spectral density) explanation
I'm trying to understand how the PSD is calculated. I've looked in a few of my Communication Engineering textbooks but to no avail. I've also looked online. Wikipedia seems to have the best explanation; however, I get lost at the part where they…
user968243
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17
votes
3 answers
Determining the "whiteness" of noise
How does one quantify how "white" some noise is? Are there any statistical measures, or any other measures (FFTs for example) that can quantify how close to white noise a particular sample is?
Kitchi
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