- #1
stabu
- 26
- 0
Hi,
Just when I thought I'd grasped the Discrete Fourier Transform properly,something comes along and messes me up ... and my books don't seem to treat it.
Say you have a square 2D image and you want to do an Ideal LowPass Filter. Well, in general, filters need to be odd-number-sized so that there is a clear center.
With a center shifted Fourier Transform, as long as the image has odd-numbered columns and rows, the center point is the DC component. That's fine if the image (and its Fourier Transform - always same number-size as image) are odd-number-sized. So you can apply a filter by multiplying each component of the image's FT.
But if the image is even-number-sized, what then? It implies you must multiply by an even-number-sized filter. In any case, your center is in fact N/2+1, when N is the dimension of your square image ... so your "center" is in fact, not in the center.
This has me in a fuddle. Sorry if I don't explain myself properly ... you'll need to have run into this problem yourself to fully gasp it.
Having said that, in general terms even-number-sized object do have center-identification problem ...
Thanks in advance for suggestions and advice ...
Just when I thought I'd grasped the Discrete Fourier Transform properly,something comes along and messes me up ... and my books don't seem to treat it.
Say you have a square 2D image and you want to do an Ideal LowPass Filter. Well, in general, filters need to be odd-number-sized so that there is a clear center.
With a center shifted Fourier Transform, as long as the image has odd-numbered columns and rows, the center point is the DC component. That's fine if the image (and its Fourier Transform - always same number-size as image) are odd-number-sized. So you can apply a filter by multiplying each component of the image's FT.
But if the image is even-number-sized, what then? It implies you must multiply by an even-number-sized filter. In any case, your center is in fact N/2+1, when N is the dimension of your square image ... so your "center" is in fact, not in the center.
This has me in a fuddle. Sorry if I don't explain myself properly ... you'll need to have run into this problem yourself to fully gasp it.
Having said that, in general terms even-number-sized object do have center-identification problem ...
Thanks in advance for suggestions and advice ...