How to make image backup of system & user partition of VZ LG G4...

I am about to flash the rooted system image for the LG G4, using the "Low Effort" root method at http://forum.xda-developers.com/g4/o...ot-lg-t3164765

Before I do that, I would like to back up my system (and perhaps my user) partitions. Since I don't have a custom recovery, I am not sure how to do that.

Can someone help me?

Thanks!

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