FYI S5 Front Camera
The picture distorts at the edges of the long axis, there is little you can do about it. The simple reason is that they used a wide angle lens to increase the capture area. S4 camera - face closeup. S5 camera - room for three but the fourth and fifth face may end up stretched. Also if you take a picture of yourself standing in front of something, it is easier for people to see the area behind you.
I also checked out the M8....the focal area combined with the high rez on front camera seems unnecessary, almost pornographic. Perhaps by intention.
My judgement the M8 focal area would be fine with 2mpix and the S5 should have had 5mpix wide angle with a distortion-free 2-3mpix face closeup.