

An Intuitive Explanation of Fourier Theory - charzom
http://sharp.bu.edu/~slehar/fourier/fourier.html

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steveplace
Let's dumb it down a little further.

<http://www.complextoreal.com/chapters/fft1.pdf>

Check page two.

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comatose_kid
This is a good document. Signals and systems was one of the more interesting
courses I took back in the day.

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steveplace
I graduated this past spring and after reading the stuff on this ladies site,
I finally get what all those classes were about.

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tel
I'm glad to see things like this on Hacker News. Sure it has relatively little
to do with the regular topics, but it's the kind of interesting thing that I'd
like to find from people who populate here.

Digital Signal Processing/Intro to Signal Processing has been one of the most
interesting classes I've taken so far.

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iamwil
Huh, I did signal processing and communication systems in college, and I don't
recall anyone ever mentioning the lens thing. It says the distance from the
image to the lens has to be "f" Is this the Nyquist frequency?

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npk
f is the focal length.

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iamwil
now I'm smacking myself. Yeah, should be obvious.

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npk
If this stuff excites you, read the first chapter of Joe Goodman's book,
_Introduction to Fourier Optics_. That's the book I read to really understand
fourier transforms.

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viergroupie
I'm a bit confused. Is the DC term always in the center of 2D frequency image?
If so, how does that provide any information about varying levels of
background luminance?

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npk
The DC term is always at the lowest spatial frequency (DC.) So, if you plot
your FT so that the DC term is in the middle, then the DC term is in the
middle :)

It provides NO information about the varying levels, it tells you something
like the sum of all the pixels / number of pixels. If you have a 10x10 uniform
image, all pixels=1, the DC term will by 1/100.

Again, the DC Term is the absoloute lowest spatial frequency, hence it's DC.

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ambiversive
The DC term also known as ao, Co, and Do (in the trigonometric, compact, and
exponential forms) is the average value of the signal over its period (if it
is periodic). It is the integral of the signal over one period divided by the
period.

