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What Is the Fourier Transform?

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Re: What Is the Fourier Transform?

#161
post #160

Earlier quoted context omitted.

> Never perceived algebra as useful in anything programming related Image, video, and audio processing and synthesis, compression algorithms, 2D and 3D graphics and geometry, physics simulation, not to mention the entire current AI boom that's nothing but linear algebra… yeah, definitely algebra isn't useful in anything programming related.

Yea that's not what I work with my guy

You said "anything programming related", not "anything related to my work", "my guy".

Re: What Is the Fourier Transform?

#162

This video [1] from a visual effects channel (Captain Disillusion) has an excellent visual illustration of how the Fourier tranform works and how its used in visual effects in his video about blurring and unblurring ("ENHANCE!") images. 1. https://youtu.be/xDLxFGXuPEc?feature=shared

I found this video from 3Blue1Brown more informative in terms of mathematics involved:

https://youtu.be/spUNpyF58BY?feature=shared

Edit: In fact it was already mentioned in the comments, but I haven't noticed

Re: What Is the Fourier Transform?

#163
post #126

Earlier quoted context omitted.

When I did EE, didn't have access to any kind of computer algebra system. Have 'fond' memories of taking Laplace transform transfer functions and converting to z-transform form. Expand and then re-group and factor. Used a lot of pencil, eraser and line printer fanfold paper for doing the very basic but very tedious algebra. Youngsters today don't know how lucky.. (ties onion to belt, etc., etc.)

No worries, as a self proclaimed youngster I didn't manage to understand Fourier in 2 days and never bothered again. Also had no other prior knowledge to algebra so maybe that's why I struggled. Never perceived algebra as useful in anything programming related, will continue to do so as most problems are solvable without it. I'll let the degree havers do all that stuff.

So you're a programmer but you've never assigned a number to a variable or written any math operations? Do you just do string translations or something?

Re: What Is the Fourier Transform?

#165

> Fourier argued that the distribution of heat through the rod could be written as a sum of simple waves. How do you even begin to think of such things? Some people are wired differently.

It didn't come completely out of nowhere, Euler and Bernoulli had looked at trigonometric series for studying the elastic motion of a deformed beam or rod. In that case, physical intuition about adding together sine waves is much more obvious. https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_t...

Other mathematicians before Fourier had used trigonometric series to study waves, and physicists already understood harmonic superposition on eg a vibrating string. I don't have the source but I believe Gauss even noted that trigonometric series were a solution to the heat equation. Fourier's contribution was discovering that almost any function, including the general solution to the heat equation, could be modelled this way, and he provided machinery that let mathematicians apply the idea to an enormous range of problems.

Re: What Is the Fourier Transform?

#166
post #146

This video [1] from a visual effects channel (Captain Disillusion) has an excellent visual illustration of how the Fourier tranform works and how its used in visual effects in his video about blurring and unblurring ("ENHANCE!") images. 1. https://youtu.be/xDLxFGXuPEc?feature=shared

While I like CD's works, I would say "CD / Blur" is the least informational of all the CD slash series. I guess it's a fun and more accessible option, but it certainly lacks depth compared to something like 3B1B's video on FT.

I like his videos and most of this particular video. For example, I agree with his choice to not discuss the nasty details of the FFT. Also, I think the "blur" part is fine, but the "unblur" part is too oversimplified.

I think he could have explained how the Gaussian filter almost kills all details / high frequency features, then rounding completely destroy them and then they can not be magically reconstructed to "unblur". He gives some hints about this, but they are to few and too general.

PS: There are some non lineal ticks "enhance" the "unblur" version , like minimizing the L1 norm of the gradient (or something like that). It helps with some images. I'm not sure which is the current state of the art.

Re: What Is the Fourier Transform?

#168
post #33

If you like Fourier, you're going to love Laplace (or its discrete counterpart, the z transform). This took me down a very fascinating and intricate rabbit hole years ago, and is still one of my favorite hobbies. Application of Fourier, Laplace, and z transforms is (famously) useful in an incredibly wide variety of fields. I mostly use it for signal processing and analog electronics.

When I did EE, didn't have access to any kind of computer algebra system. Have 'fond' memories of taking Laplace transform transfer functions and converting to z-transform form. Expand and then re-group and factor. Used a lot of pencil, eraser and line printer fanfold paper for doing the very basic but very tedious algebra. Youngsters today don't know how lucky.. (ties onion to belt, etc., etc.)

I just recently got my Computer Engineering degree which is the modern Electronics Engineering and we had a whole class on transforms. We had to do it on paper, but that professor at Cal State LA knew what the heck she was doing. We learned it good.

Re: What Is the Fourier Transform?

#169
All these comments and no Steinmetz mention. The original papers he wrote applying the transforms to electrical engineering work are so genius and simplifying for the craft, and he's such a nicer person for one of the founders of the field of EE. Also the origin of that old story about $10 for hitting the machine with a hammer $9990 knowing where to hit it, from what I can gather.

Re: What Is the Fourier Transform?

#170
Can somebody eli5, im an amateur. How does the transform know the frequencies of the output. Do you have to specify a number n, and then it decomposes it into n frequencies. Or do you give it a list of frequencies, and then it decomposes the coefficient or amplitude or something for each?

I guess what i want to know, in the examples it always shows like 3 or 4 constituents frequencies as output, but why not hundreds or a million? Is that decided upfront /paramtetizable?

The article isn't helpful, it just says something like "all possible frequencies".

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