This is a post for comic book artists preparing their pages for their publisher or colourist. I’m aware that many pros still don’t know some of this stuff, often because the bigger publishers have production teams who will take the incorrectly sized or shaped pages and adjust them before passing on to colourists or for print. However, this a) is giving more work to people that you can easily do yourself and b) reduces the amount of control you have over how your work is printed. It makes sense to provide files that will present your work in the best way possible.
So, the basics of a digital page file: