compute the period of a texture image by FFT

Question

I have a texture image, which has some local shape distribute evenly or unevenly. I want to compute the period of these local shapes by FFT. Can anybody help me?

Here is the image:

Magnitude after FFT:

Phase after FFT:

Answer 1

The magnitude is what you need. The strong East-West lines in the FFT are the result of a repetition in that direction. Indeed, when you look at the actual texture, you see that the bands indeed repeat.

There's a limited structure orthogonal to those bands, as we can see from the fact that we have 3 evenly spaced East-West lines.

The 3 lines aren't exactly East-West; they're rotated by about 10 degrees clockwise. That's also true of the initial image, where the bands are also rotated. The period of the texture is given by the distances between the 3 lines as well as the intensity changes along those lines.