What is the meaning of the length of diagonal lines in FFT I am relatively new to FFT analysis of images and have a question about them. I like to think I understand the basics but many of the properties shown in a FFT image are beyond me.

My main question is what is what is the meaning of the length of diagonal lines in a fourier transform? What is the meaning of the length of a diagonal line on the image domain or in the Fourier domain? The diagonal lines are related to the edges in the image but what kind of property does the length describe?



If asking these questions means that I don't fully understand FFT, are there any resources that would help me dig deeper?
If you rotate an image (2D function), its 2D Fourier transform also rotates.

Those lines mean you have something like a barcode oriented in that direction in your image. In one direction it has lots of variations and behaves like a white noise with flat spectrum and in the other direction it has very slow variations.

I'm not sure what do you mean by the length of diagonals, but it's a visual measure of maximum frequency available in those directions.