Question on how PSNR is calculated on a minibatch

[Seeker98]

Hi, I'd like to ask how is PSNR calculated on multiple images, for example, I have two 4-dimensional tensors with layout (N,C,H,W), PSNR here is simply calculated over all datas, or on the last 3 dims, and taking mean over first dim?
I'm a little confused about the calculation method, especially on default settings and params. Also, If I want to calculate on the last 3 dims and take max/avg on the first dim, what params should I use?
Thanks for your reply in advance.