why do i get "Array indices must be positive integers or logical values ?"

%  folder in which your images exists
location1 = 'C:\Users\User\Documents\MATLAB\FYP-DCP (jaja)\dataset-hazy\*.png'; 
location2 = 'C:\Users\User\Documents\MATLAB\FYP-DCP (jaja)\dataset-ori_img\*.png';  

imdshazy = imageDatastore(location1);
imgs = readall(imdshazy);

imdsori = imageDatastore(location2);
imgO = readall(imdsori);

[m, n, p, l] = size(imgs{1}); % m=height, n=width
image = zeros(m,n,p,l);
res_im = imresize(imgs{i}, 0.4);

[m, n, p, l] = size(res_im);
image2 = zeros(m,n,p,l);
imagedehaze = zeros(m,n,p,l);
image3 = zeros(m,n,p,l);

for i =  1:1:54
    image2(:,:,:,i) =  imresize(imgs{i}, 0.4);
    imagedehaze(:,:,:,i) = dehaze(image2(:,:,:,i), 0.95, 5);
    image3(:,:,:,i) =  imresize(imgO{i}, 0.4);
    resultpsnr = psnr(imagedehaze(:,:,:,i), image3(:,:,:,i))
end 

Answer 1

[Voss]

res_im = imresize(imgs{i}, 0.4);

is before the i loop, so i is not defined, so MATLAB interprets that i as the imaginary unit 1i. Probably you meant imgs{1} there.