Understanding 2D FFT result of an image having a pattern I have created Fast Fourier Transform (FFT 2D) of the following image (without pattern angle markers) using ejectamenta online tool.

Input (Original image is here)



Output I got is the following



As well as input pattern 66 deg gives output with 48 deg maximum magnitude line. (angles are measured approximately). But I believe Fourier pattern should be perpendicular to the input image pattern. But it has a difference. How this happens and what is the problem here. Could someone please explain? I'm trying to derive pattern direction using it's FFT result. Thank you.
I found that FFT output depends on aspect ratio of the input image. Fourier pattern is perpendicular to the input image pattern only if the input image has same width and height.