So, When we take the FFT of any Composite or Single Sine Wave we get exact frequency on x-axis of the plot. The point where we get the original frequency in FFT is depend upon the Sampling Rate and the Length of the actual signal, i.e
If there is Sine wave of 100KHz
and the Sampling Frequency equals to 1MHz
, and If we are plotting the 10 Oscillations i.e t = 10/f
then the length of the Signal would be 100
.
and If we plot the FFT of that signal than the First point in FFT represent 10KHz
i.e 1MHz/100 = 10KHz
. So the actual signal frequency will be plotted on the 10th
point of FFT graph, ( 10KHz*10 = 100KHz ).
This is how we can see the Frequency of our actual signal in Frequency domain.
but what about an Image ?
Consider a binary 8x8
image ,
image = [zeros(8,4) ones(8,4)]
image =
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
0 0 0 0 1 1 1 1
The FFT will be calculated for each row and for each column which mean the number of samples to calculate each FFT will be 8.
I know that the FFT values have no frequencies, it has only complex amplitudes, then how does the FFT is plotted for image, How can identify the actual frequency like i did in case of Sine wave by dividing the Fs with length of Signal ?
Here is 1D FFT of the Signal,
x = [0 0 0 0 1 1 1 1]; %what are the frequencies here
% Samples = 8
f = fft(x)
plot (abs(f))
Can somebody explain me please what are the frequencies in the FFT plot ! ??? I just need one good example that explain the graph of FFt of this signal like i did for a sine wave.