Quantitative evaluation of the images generated by GAN

Hi,

I run the codes at https://www.mathworks.com/help/deeplearning/ug/train-generative-adversarial-network.html

and want to evaluate the similarity of the generated images with their originals.

I wan to use these quantitative metrics: SSIM, Mean Square Error (MSE), or Peak Signal to Noise Ratio (PSNR).

So, I need two images: 1)Generated image, 2) The original image to match with the generated image

I used the following code to get each generated image separately

I = extractdata( dlXGeneratedNew );
img = I (:,:,:,idx);

But I don't know which original image should be used with which generated image.

Could you please help, how to do this quantitative evaluation?