Logic while training FFDNET

[AnasShahzad1996]

In your file model_train.m, you multiply the sigmas with an array of random numbers. Since randn produces negative numbers such as -3.14, the sigma will exceed 75 in the image. My question is that why do you multiply the sigmas with that array

K = randi(8);
labels = imdb.HRlabels(:,:,:,batch);
labels = data_augmentation(labels,K);
sigma_max = 75;
sigmas = (rand(1,size(labels,4))*sigma_max)/255;
<-------------- This line! ------------------>
new_arr = bsxfun(@times,randn(size(labels)), reshape(sigmas,[1,1,1,size(labels,4)]));
inputs = labels + new_arr;