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.