How to find wavelength of a surface that I have generated using fft2?

Hi, I have a surface profile like the first image. I performed fft2 to find the second image. x and y-axes values are in pixels. I have 2 questions.

1. What does the second image mean physically?
2. Most importantly, how to find the wavelength present in the surface?

[David Goodmanson]

Hi Mustafa,

since the first image is in color, how do you deal with taking the fft? Is this a case where the image is basically a grayscale image, with color being supplied by a color map with an assoiciated color bar?

[Mustafa Rifat]

yes. The color is representative of height at different points, mathced by a colorbar.