power spectrum plot of an image
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I am quite new to signal processing and matlab, and I have begun (a small project) to calculate the power spectrum of an image in the frequency domain - and plot this against the frequency.
So, what I have till now is the following:
close all; clear all;
img = imread('my_pic.jpg','jpg'); % it is a color image 400px x 400px
img = rgb2gray(img); % change to gray
psd = 10*log10(abs(fftshift(fft2(img))).^2 );
So far it looks good - I get the mesh plot which resembles the spectra I see in various academic papers.
However, what I am looking for is a graph plot of this power spectra Vs. the frequency - and I am not entirely sure how to get this frequency vector for the image. I could do say:
N=400; % the image is 400 x 400
f=-N/2:N/2-1; % possible frequencies?
.. but I am not convinced this is entirely correct.... I'd really appreciate if someone could point me in the right direction to plot log frequency Vs. the power spectrum.