Question [Q] How to backup full system to an 'image' (firmware.img) file?

Hello, I'm new here but have installed newer or modified operating systems on tablets, using RKbatch tools. You just set your tablet to USB debugging mode on, connect it to your PC, and RKbatch program 'sees' your tablet, then asks what firmware .img file to use.

What I'd like to know is how do I make a backup firmware image file of my tablet's system? I've tried using Titanium Backup, but it only copies all the tablet's files one by one into a folder. It does not make this 'img' file. I want to put some different firmware on my tablet, but want to be able to restore using RKbatch tools to reinstall the original firmware if I don't like what I just installed.