Awesome

img2sdat

Convert filesystem ext4 image (.img) into Android sparse data image (.dat)

This binary requires Python 2.7 or newer installed on your system.

It currently supports Windows x86/x64, Linux x86/x64 & arm/arm64 architectures.

img2sdat.py <system_img> [-o outdir] [-v version] [-p prefix]

<system_img> = input system image
[-o outdir] = output directory (current directory by default)
[-v version] = transfer list version number (1 - 5.0, 2 - 5.1, 3 - 6.0, 4 - 7.0, will be asked by default, more info on xda thread)
[-p prefix] = name of image (prefix.new.dat)

This is a simple example on a Linux system:

~$ ./img2sdat.py system.img -o tmp -v 4

It will create files system.new.dat, system.patch.dat, system.transfer.list in directory tmp.