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image-processingsignal-processingfftwindowing

2D FFT of an image shows some invalid values for high frequencies

I uploaded my 2D FFT magnitude image here:

enter image description here

If you take a look at it, for high frequencies[right, left, top and bottom], only at around x and y-axis, there are some points with high power[yellow color]. These points shouldn't be in the resultant FFT2, since I know the original height image is isotropic and therefore the 2D FFT must look something like the example below(just note high frequencies):

enter image description here

Now, the question is, what could be the possible reasons for such behavior at high frequencies?

added: Here is the magnitude power spectrum before windowing:

https://dl.dropboxusercontent.com/u/82779497/nowin.png

here is the original image, which is a height profile recorded by a profilometer: https://dl.dropboxusercontent.com/u/82779497/asph5.jpg

By the way, I export data as a .txt file from profilometer software to Matlab.

Solution

  • The profilometer we use for capturing the surface image, uses fringe projection method which produces some artifacts along the projected stripes on the surface. So, the problem lies on the device we are capturing images with.

    Thanks for comments Eddy.