I manage to get the GS4 Camera apps running on GS3 JB 4.2.1 Leaked Version. Is still buggy but still usable for normal photo taking task. While working to fix the bugs, I thought of sharing this mod for anyone who wish to try this and maybe someone could help in fixing the bugs.
Here is a video of this apps running on S3 prepared by udimars30:
What is working and not working
1) Rear camera works fine up to 8mp setting. Could take photo with setting at 13mp but result is terrible.
2) Front camera works fine too.
3) Flash is working
4) Video recording is not working!
5) Beauty Face feature working
6) Best Photo feature working
7) Best Face feature working
8) Sound&Shot feature seem working
9) HDR feature working
10) Eraser feature working
11) Panorama not working
12) 360 feature not working
13) Sports feature working, I think so.
14) Night feature working
15) Effects like sepia, vintage, etc, not working
16) And Dual camera...too bad, is not working
17) Others settings - not yet tested.
Allright, if you wish to try, here is how:
(As usual, flash this at your own risk)
1) Make sure you are on Deodexed Samsung JB4.2.1 (XXUFMB3)
2) Download the zipfile below
3) Backup your phone.
4) Clear cache & Dalviks cache in cwm/twrp
5) Flash the zipfile
Thanks to Henrylife for sharing idea and suggestion
Thanks to TekGadgt for the S4 system dump.
Thanks to udimars30 for the video.
GS4 Camera for GS3 (XXUFMB3) ( name of zipfile is just typo, it is for S3)