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Apr
7
comment How to use 2D Fourier analysis to clean the noise in an image
@yode I added the image, but it gets converted to png, nonetheless. I did not put it in because I felt the post was already too big. I had a few other examples (with a periodic Table-generated mask and some degree of fading) but it's waaaay too long already.
Apr
7
revised How to use 2D Fourier analysis to clean the noise in an image
Made the tile more specific to image processing. Hope the OP agrees.
Apr
7
revised How to use 2D Fourier analysis to clean the noise in an image
added requested image and fixed some more of my lousy grammar (I guess my error is fractal-like)
Apr
7
awarded  Good Answer
Apr
7
revised How to use 2D Fourier analysis to clean the noise in an image
Added an example of filtering based on knowledge of the structure
Apr
4
awarded  Yearling
Apr
1
comment Can I plot the solution to an ODE without using dsolve?
You can plot a derivative field. For every point (t,x) you draw a little segment slanted according to the value of the derivative x'(t). That's your right hand side of the equation. You are basically plotting the solution without solving the equation (well, when you plot those little segments, you'll understand...) Then from that derivative field you can gain insights on how your solutions would behave. Ty to see if you can make out a solution that has the same value at t=0 and t=2pi.
Mar
28
revised How to use 2D Fourier analysis to clean the noise in an image
Still trying to correct my grammar. Expanded explanation. Apologized for bad coding.
Mar
28
comment How to use 2D Fourier analysis to clean the noise in an image
@DanielLichtblau , I'm flattered. Yes, you can of course use graded profiles and one could generate them directly as density matrices. What I've posted here is just a collection of hacks that need refinement (for example, the scaling of the spatial frequencies - look at Karl's FFT: I should have used an elliptical shaped filter to make it uniform), but I did not want to put too many irons in the fire. But I will add a few more examples later on - this old notebook of mine is full of surprises!
Mar
27
awarded  Enlightened
Mar
27
awarded  Mortarboard
Mar
27
comment How to use 2D Fourier analysis to clean the noise in an image
@yode, that is the exact image that I used. zKarlSrGIF.gif. The only difference is that I had it renamed Karl.gif. Are you using the same (not ideal, since it creates white artifacts) procedure GrayScaleMatrix to convert it to grayscale? My starting point in both examples are both the grayscale matrices, so the original color picture is irrelevant (as long as you get the same grayscale one from them)
Mar
27
comment How to use 2D Fourier analysis to clean the noise in an image
There you go: klccgo.com/index.html (I used this tool: tineye.com - that image is the only one result in 14.5 billion images). It's Karl Lambrecht, pioneer of calcite mining. As for phase spectrum, you need holograms AFAIK. I've never used a periodogram for optical filtering. But I will add a complementary example to Donald's filtering, where you keep the periodic features of the image and discard the rest.
Mar
27
revised How to use 2D Fourier analysis to clean the noise in an image
Fixed my lousy, lousy, lousy grammar. Also tried to clean up my act.
Mar
27
awarded  Nice Answer
Mar
26
comment How to use 2D Fourier analysis to clean the noise in an image
I've edited the post to give another example with random noise (it can be applied to Lena, by suitably scaling the mask). As for the phase, well, phase contrast microscopy is based on phase filters. I refer you to the book by Steward for that.
Mar
26
revised How to use 2D Fourier analysis to clean the noise in an image
Added a low-pass filter example and bibliography
Mar
26
revised How to use 2D Fourier analysis to clean the noise in an image
Added a low-pass filter example
Mar
26
revised How to use 2D Fourier analysis to clean the noise in an image
added 257 characters in body
Mar
26
revised How to use 2D Fourier analysis to clean the noise in an image
Added source image. Reproduced here in accordance to fair use for educational purposes.