🚀 go-pugleaf

          Merry Christmas to everybody,
I would like to ask a question about standard image "Lena" with size of
512x512x8bit.
For this digitalized image, we can use 2D-FFT (with input data length 512)
to estimate the spatial frequency property of H(wx,wy),where wx and wy
are spatial frequences in X-direction and Y-direction,respectively.
And generally, wx and wy are normalized to [-pi,pi] as following figure.
                      wy|
                        Pi
                        |
                        |
           --  -Pi------o-------Pi--->wx
                        |
                        |
                       -Pi

My question is that,
for wx and wy, what are the real frequencies (in Hz) at Pi ?
The answer may be related to the sampling frequency f_s for 512x512 images,
What is the f_s?  and for 256x256 images, does the f_s become half of 512's?

Thanks in advance.
-Jie Chen
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____________________________________________________________________________              
               Jie Chen 
	       ITL ( Information Transmission Laboratory )
               Depart. of Electronics
               Univ.   of Electro-Communications 
               Chofu city, Tokyo 182, Japan
               E-mail: chen@mahler.ee.uec.ac.jp
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