Filtering in the frequency domain

Hello everyone,

I am just getting into matlab and and working through some projects for digitam image processing. I wrote some matlab code to filter in the frequency domain but when I plot my image at multiple points I am getting issues from the expected results. I believe the issues are plotting and data type related and wanted to get some feedback on how to do things better.

I need to accomplish the following:

1. Given an input f(x,y) of size M x N obtain the padding sizes P and Q. P = 2M, Q = 2N.
2. Form a padded image fp(x,y) of size P x Q using zero padding.
3. Center the image using fp(x,y) * (-1)^(x+y)
4. Compute the DFT F(u,v) of the image from step 3.
5. Construct a real symmetric filter transfer function H(u,v) of size P x Q with center at (P/2, Q/2).
6. Form the product G(u,v)=G(u,v)*H(u,v) using element wise multiplication.
7. Obtain the filtered image by computing the IDFT of G(u,v), and decenter the image. gp(x,y) = (real[IDFT{G(u,v)}])*(-1)^(x+y)
8. Obtain the final filtered result g(x,y) of the same size as the input image by extracting the M x N region from the top, left quadrant of gp(x,y).

I have written the following code to filter my image and accomplish the steps above (thanks to lots of helpful answers on this website).

Question:

In my figure F_uv_dftImage I should see a periodic frequency spectrum. I can but I need to zoom in really close currently to see a tiny image. In the book im using they show this a lot more clearly. Am I using the wrong data types throughout my code (double) to get the results? Or am I just plotting these graphs in the wrong way to display the data? Any input would be great!

If you want to see my code please just message me directly.

[Uzair Muhammad]

can you please share the code. thanks in advance

Email : [e-mail]

Answer 1

[Aleksander Banbur]

I solved my problem. In order to plot the DFT properly you need to scale it logarithmically. You can use the log transformation which is s = c*log(1+r) where r is the input DFT image normalized (r=DFT_Image/255), c is a constant, and s is your new log scaled image which you can plot. This fixed all my issues.

Answer 2

[alo halo]

I cannot find the direct message option. Can you please share your code with me?