There's a way to get most of them back. First root the phone. Then download
munky-tool to your computer and read through it to see how it's done. Create an image of the userdata partition to your computer (using adb), then run
PhotoRec on the image file to recover all the files in it. (If munky-tool doesn't read like English to you, find a friend who can use a Linux command line to do it for you.)
You could also just run munky-tool from the phone, but every time you write anything to the phone you risk overwriting one of the files you're trying to recover.
(BTW, you do know that the whole idea of a factory reset is to delete all your files and personal data, right? There's no other reason to use it. [Even using it to fix a bootloop just removes the app that's causing the bootloop.])