I think I’m misunderstanding the meaning of batch size…
I googled about batch size and it says
Batch size  is a term used in machine learning and refers to the number of training examples utilized in one iteration.
If this is right than 100 training data should be loaded in one iteration.
What I thought the data in each iteration is like this.
(100/60000)
(200/60000)
(300/60000)
…
(60000/60000)
but I just found out that printing out the X, and Y in inner for loop, it was 600 data and which will lead to 100 iteration in one epoch.
result was same in the very top previous code about img and mask(batch size = 1).
what I wanted to make was getting 1 data in inner loop instead of whole 3607 data.
If i’m misunderstanding the concept of batch size, then is the  batch size == number of iteration???