I’m working on a image signal project using C++ with DFT, IDEF.

I major in physics and have lots of experience dealing with 1d fourier transform..

HOWEVER, 2d dft is really not intuitive.

I studied a lot and now have a little understanding of what is 2d dft.


In 1d, assume you have 2 functions each having frequency 30, 60(ignore unit).

then I can have a sine function with frequency 30, 60.(spatial domain)

When I take DFT to each sine function, I got value of 30,60 in frequency domain.

*** If I reduced the value of frequency (f = 30), then I get low amplitude in spatial domain, which means Asin(2pi30x), coefficient A reduce.

alright then.

when I have a image of 100x100 pixels and take 2d dft.

Then I also have 2d frequency domain(only magnitude).

*** What happen to pixels in spatial domain when I reduce the value of specific frequency?

suppose we have two frequency (10,10), (20,20) in frequency domain(u,v)

this means image in spatial domain is composed of these two frequency sinusoidal functions.

Also same as 1D, when I reduced the value of the specific frequency, I thinks it should reduce the amplitude of 2d sinusoidal function,, right?

Then How can i interpret pixel?

*** what can I interpret pixel in regard to sinusoidal function.

This question arises because I and colleague are working on project,

we are inserting specific frequency like (30,30) in frequency domain to original 1 image.

then after, when I idft, I got image what i want.

But my colleague is trying to insert frequency not in frequency domain, but in spatial domain, dealing with pixel value, which I can’t understand…

  • $\begingroup$ You are aware that the IFFT just adds up all the sine waves, righT? $\endgroup$
    – user253751
    Feb 10 at 14:37
  • $\begingroup$ @user253751 Yes I know! $\endgroup$ Feb 12 at 23:51
  • $\begingroup$ then you might see that adding a single pixel into the FFT adds a sine wave into the IFFT $\endgroup$
    – user253751
    Feb 13 at 11:50


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