# Selecting a point in the 2D FFT and Complex Windows simultaneously

The frequency and direction of the 2D DFT of an image are available on the FFT plot, which indicates the frequency as r in pixels/cycle, and the direction in degrees as theta (\theta).

On the other hand, the amplitude and phase can be retrieved on the Complex plot, at any point in the (x,y) coordinate system. The complex plot comes stacked-up in its **Re**al and **Im**aginary components.

This is explained by Herbie here.

The (apparent… well… my) problem is that both plots (FFT and Complex) appear on the screen separately. So if I want to gather the four values of the 2D DFT for a given point I need to first point-select on the FFT plot, which will print out the corresponding frequency and direction values, together with the Cartesian coordinates of the point ( (167, 119) in the animated GIF below), and then go fishing over the Complex plot for the point in question by hovering over, and keeping a steady hand, until the correct value appears on the display.

I have tried stacking up both plots (FFT and Complex) without success.

The question is: Is there a way to select a point in both the FFT plot and the  Complex plot simultaneously, or somewhat more expeditiously?

Here is an illustration of the problem:

Thank you.

Dear @Toni
I really think you can use the Syncrhonise Windows under Analyse->Tools

and then you can add points at the same coordinates.

have a nice day,
Emanuele Martini

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Good day Toni,

Your problem doesn’t differ from the previous one. You just have to add the log. power spectrum to the complex stack. You state that this doesn’t work for you but it does for me …

Make sure the log. power spectrum is 32bit (Image > Type > 32-bit), then use “Image > Stack > Tools > Concatenate…” with

Image 1: FFT of Image
Image 2: Compley of Image

The result is a stack with three slices and you may then use the Point Tool with “Auto-measure” and “Auto-next slice” checked.

Regards

Herbie

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Thank you very much! It worked like a charm. I have posted a how-to animated gif for other novices here, giving you credit.

1 Like

Thank you very much for your help today, and on your previous post, which made a huge difference. I have posted a how-to animated gif for other novices here, giving you credit.