facing error in the below code. please help

% Parameters
inputImage = imread('cameraman.tif'); % Load the input image
integrationTime = 0.1; % Integration time for photon counting

% Step 1: Initialization
[height, width] = size(inputImage);
H1 = exp(1i * 2 * pi * rand(height, width)); % Random phase mask 1
H2 = exp(1i * 2 * pi * rand(height, width)); % Random phase mask 2

% Step 2: Encryption
inputImage = double(inputImage);
S = inputImage .* H1; % Intermediate image
S_hat = fftshift(fft2(S)); % Spectrum of intermediate image
E_hat = nonlinearOperation(S_hat); % Nonlinear operation on the spectrum
E = ifft2(ifftshift(E_hat)); % Encrypted image

% Step 3: Photon Counting
photonCounts = countPhotons(E, integrationTime); % Photon counting simulation

% Step 4: Decryption
E_hat_restored = inverseNonlinearOperation(E_hat); % Inverse of nonlinear operation
S_hat_restored = E_hat_restored .* conj(H2); % Restored spectrum
I = ifft2(ifftshift(S_hat_restored)); % Decrypted image

% Display results
figure;
subplot(2, 2, 1); imshow(inputImage, []); title('Input Image');
subplot(2, 2, 2); imshow(abs(E), []); title('Encrypted Image');
subplot(2, 2, 3); plot(photonCounts); title('Photon Counts');
subplot(2, 2, 4); imshow(abs(I), []); title('Decrypted Image');

% Load the original input image and the decrypted image
originalImage = imread('cameraman.tif');
decryptedImage = imread('decryptedimage.jpg');

Error using imread>get_full_filename
File "decryptedimage.jpg" does not exist.

Error in imread (line 372)
fullname = get_full_filename(filename);

%{ 
Resize the images if they have different sizes
if ~isequal(size(originalImage), size(decryptedImage))
    originalImage = imresize(originalImage, size(decryptedImage));
end
%}
% Convert images to double precision and scale to the same data range
originalImage = im2double(originalImage);
decryptedImage = im2double(decryptedImage);

% Calculate MSE
mse = mean((originalImage(:) - decryptedImage(:)).^2);

% Determine maximum pixel value
maxPixelValue = 1; % Modify accordingly based on the data range

% Calculate PSNR
psnr = 10 * log10((maxPixelValue^2) / mse);

% Display the PSNR value
fprintf('PSNR: %.2f dB\n', psnr);


% Functions


function E_hat = nonlinearOperation(S_hat)
% Perform desired nonlinear operation on the spectrum
% Example: Squaring the spectrum
E_hat = S_hat.^2;
end

function photonCounts = countPhotons(E, integrationTime)
% Simulate photon counting by sampling the intensity values
% and counting photons within the integration time
photonCounts = sum(E(:)) * integrationTime;
end

function E_hat_restored = inverseNonlinearOperation(E_hat)
% Perform inverse of the nonlinear operation on the spectrum
% Example: Taking the square root of the spectrum
E_hat_restored = sqrt(E_hat);
end

[DGM]

What error? I have to ask, because it's not obvious without the image you were using. My guess is that it's not the same size. Given that it's a JPG, it's probably RGB.

[Ranjeet]

I tried to run the provided code with the input image (‘cameraman.tif’) and another ‘JPG’ image of same dimension (treated as decrypted image). The code ran without any error. Providing the decrypted image might help.

Answer 1

[Drishti]

Hi Anshika,

While reproducing the provided code on my end, I encountered the same issue of ‘decryptedimage.jpg does not exist’.

This error can be resolved by loading the decrypted image into the current work directory. If the decrypted image is getting generated from the provided code, then saving it will resolve the error. You can refer to the code snippet to save the image.

% Save the decrypted image
imwrite(abs(I), 'decryptedimage.jpg');

Also the empty ‘Photon Count’ plot can be rectified by utilizing the ‘intensity’ for the calculation of ‘Photon Count’.

Refer to the implementation below:

function photonCounts = countPhotons(E, integrationTime)
    % Calculate intensity
    intensity = abs(E).^2; 
    photonCounts = poissrnd(intensity * integrationTime);
end

For more information, you can refer to the MATLAB Documentation of ‘imwrite’ function:

https://www.mathworks.com/help/releases/R2024b/matlab/ref/imwrite.html

I hope this resolves the issue.