Dear ptrblck, thanks again for the response.
So sorry for being absent these past weeks, haven’t had time to work on it properly.
I tried using your code adapted to my needs but no success so far. Even though the image only appears to have black and red on it, the code is still returning all values from range [0,255].
What I tried to do is apply this snippet to probe for problems:
testmask = Image.open(mask_path[0])
testmask = tvtransforms.Resize((std_size, std_size))(testmask)
pix_val = list(testmask.getdata())
print(pix_val)

pix_val is returning already different values from (0,0,0) and (255,0,0), which are the values I expect from a mask presenting only red and black pixels (please remind that the dataset was built from the coding presented on the dict we were discussing previously).
So is it an indication that the mask itself could be the problem? Or am I missing something?
Dataset I am currently using: SUIM Dataset 1.
I kindly appreciate the support so far!