specifying a selection in Fourier transform

[Michael Elbaum]

Dear all,

Filtering in Fourier space usually involves setting a mask at the center with some diameter or height/width, and then erasing either inside or outside before back-transforming. Selecting the area is always tricky by hand. For real space images one can specify coordinates in Edit > Selection > Specify... This doesn't work well on FFTs. The center is not recognized and the size appears in pixels rather than units/cycle. It would be a great help to be able to specify the reciprocal space cutoff directly. Perhaps there's an added plugin that does this already? any help appreciated.

thanks,
Michael

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[Rasband, Wayne (NIH/NIMH) [E]]

> On Nov 30, 2015, at 4:49 PM, Michael Elbaum <[hidden email]> wrote:
>
> Dear all,
>
> Filtering in Fourier space usually involves setting a mask at the center with some diameter or height/width, and then erasing either inside or outside before back-transforming. Selecting the area is always tricky by hand. For real space images one can specify coordinates in Edit > Selection > Specify... This doesn't work well on FFTs. The center is not recognized and the size appears in pixels rather than units/cycle. It would be a great help to be able to specify the reciprocal space cutoff directly. Perhaps there's an added plugin that does this already? any help appreciated.

The latest ImageJ daily build (1.50f8), adds a Process>FFT>Make Circular Selection command. The cutoff in units/cycle is displayed in the status bar as you change the selection radius using the slider in the dialog box.

-wayne

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[Michael Elbaum]

Amazing :-) the slider shows pixels and the status bar shows units/cycle. a huge improvement for FFT analysis!
thanks,
Michael

________________________________________
From: ImageJ Interest Group [[hidden email]] on behalf of Rasband, Wayne (NIH/NIMH) [E] [[hidden email]]
Sent: Tuesday, December 01, 2015 04:02
To: [hidden email]
Subject: Re: specifying a selection in Fourier transform

> On Nov 30, 2015, at 4:49 PM, Michael Elbaum <[hidden email]> wrote:
>
> Dear all,
>
> Filtering in Fourier space usually involves setting a mask at the center with some diameter or height/width, and then erasing either inside or outside before back-transforming. Selecting the area is always tricky by hand. For real space images one can specify coordinates in Edit > Selection > Specify... This doesn't work well on FFTs. The center is not recognized and the size appears in pixels rather than units/cycle. It would be a great help to be able to specify the reciprocal space cutoff directly. Perhaps there's an added plugin that does this already? any help appreciated.

The latest ImageJ daily build (1.50f8), adds a Process>FFT>Make Circular Selection command. The cutoff in units/cycle is displayed in the status bar as you change the selection radius using the slider in the dialog box.

-wayne

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