What is the difference between item_tfms and batch_tfms? I am confused whether all images are first cropped out (say randomly) for every epoch, using item_tfms, and then batch_tfms is applied to a batch of such cropped image? or is a batch chosen first, transformed using batch_tfms, and then all are cropped out using item_tfms? What is the correct order of processes?
In general, what is the idea behind having batch transforms and item transforms as two separate processes?