How to Fourier Phase Scramble a specific area of an image?
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Hi. I have a set of face images that I want to Fourier Phase scramble, excluding the pixels outside of the face contour. This is a sample image (see below): All the pixels outside the fase contour have the same RGB values. I need to Fourier Phase scramble only the pixels inside the contour; in other words, the pixels that belong to the face. Could anyone help me with the code? I'm not very experienced at image processing! Thanks so much in advance!
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1348799/image.jpeg)
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Nayan
2023-4-11
Hi,
As I understand you need to perform phase scrambling on the image. Phase scrambling is a technique used in signal processing to disrupt the phase information of a signal while preserving its power spectrum. In Matlab, you can perform phase scrambling on a signal using the following basic steps :-
- Read the image using "imread(filename)".
- Calculate the FFT of the image using fft2(X)
- Extract the magnitude and phase information from the obtained FFT.
- Scramble the phase by multiplying with a random phase.
- Recreate the FFT by multiplying the random phase with the magnitude of the original image.
- Taking in IFFT using ifft2(x) will provide the phase scrambled image.
Hope this helps!
Refer the following code sinppet for help.
im = imread('image_file_name');
% Convert the image to grayscale
im_gray = rgb2gray(im);
% Compute the Fourier transform of the image
im_fft = fft2(double(im_gray));
% Extract the magnitude and phase information
im_mag = abs(im_fft);
im_phase = angle(im_fft);
% Randomize the phase information
[N,M] = size(im_phase);
rand_phase = exp(2*pi*1i*rand(N,M));
im_phase_scrambled = im_phase.*rand_phase;
% Combine the randomized phase information with the original magnitude information
im_scrambled_fft = im_mag.*exp(1i*im_phase_scrambled);
% Compute the inverse Fourier transform to obtain the phase-scrambled image
im_scrambled = ifft2(im_scrambled_fft);
% Convert the phase-scrambled image back to uint8 data type
im_scrambled = uint8(real(im_scrambled));
% Display the original and phase-scrambled images side by side
subplot(1,2,1), imshow(im_gray), title('Original');
subplot(1,2,2), imshow(im_scrambled), title('Phase-scrambled');
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