Well, thanks to fguy, this thread http://forum.xda-developers.com/show....php?t=1054836 provided me the necessary inspiration to investigate just exactly what are these img made of.
Hopefully, this will allow easy removal of all the Samsung junk, deodexing, rooting etc etc without going through adb.
As it turns out, they are simply sparse ext4 images, and the AOSP source tree already contains the necessary utilities to both unpack and repack these img files via "ext4_utils" in system/extras (https://android.googlesource.com/pla...system/extras/)
For your convenience, I have provided a repackage of the source code for ext4_utils with a simple Makefile, for keen developers to make the necessary tools for unpacking and repacking the stock img files. Making these tools requires a linux development environment, which is beyond the scope of this topic.
To make the tools, simple extract the attached source code and type "make".
To unpack the .img file:
./simg2img factoryfs.img output.img
mkdir tempdir; mount -o loop output.img tempdir
./mkuserimg.sh -s /some/directory/with/files ./factoryfs_custom.img ext4 ./temp 512M
I have just tested repacking the stock factoryfs.img. It so happens that the original ext4_utils does not properly preserve permissions on the new ext4 image. I have made a slight modification to the source and reuploaded the zip.
You can now successfully unpack, remove and change the stock apps, root and modify the stock image using instructions above!!
I hope this will help people create their own custom roms.
UPDATE 27th MAY FOR GALAXY S4 TESTING (i9500 i9505)
A few people have messaged me asking why these tools do not work for the new Galaxy S4. Unfortunately I do not have a Galaxy S4 so I can not test any of these utilities. HOWEVER, it seems there has been quite a bit of updates by Google in the ext4_utils package. I have updated the sources according to 4.2.2 which is the latest version of the tools. I must stress that I DO NOT HAVE A GALAXY S4 TO TEST so don't be expecting miracles. In any case I have uploaded the new code now. As it was before, I have provided a MAKEFILE and you simply type "make" in order to build the tools. They are contained in ext4_utils_new.zip.
Thanks for your support guys. And I do apologize for replying late to my inbox...
Update 9th November 2014
Thanks to qwerty_7564 for providing the fixes for cygwin compilation.
Ext4 utils new still missing link arguments to compile. Investigating. I will update the sources to that of the 4.3 branch later.
Update 3rd December 2014
I have updated the tools to 4.3 branch. Note that no attempts has been made to make this compatible with cygwin as I have no cygwin to test.
As I have mentioned earlier, I do not have a newer samsung device to test any of these files, use at your own discretion. The new files are in ext4_utils_r4.3.tar.gz and is based on the jb release 2.0.0 branch.