Readings the output of the FFT of the picture of a circle in ImageJ at some random point (163,128) I get X_{\text{Re}}=-0.182 and X_{\text{Im}}=-3.854, using the `Complex`

plot (yellow dot). The `value`

on the output on the `FFT`

plot is 32 (cross cursor symbol):

I don’t understand why the relation between this latter value (32), which I presumed it was the amplitude, and the real and imaginary components, i.e. \vert X[k]\vert=\sqrt{X_\text{Re}^2+X_\text{Im}^2}, is not fulfilled.