This is found in the original akaze repo. Previous sub pixel localization method assumes the coordinate (0, 0) is the up-left corner of the up-left pixel. But as far as I know, opencv uses the center of the up-left corner, in this case it should be done in this way.

https://github.com/pablofdezalc/akaze/commit/35aeb83a7142e9ec42419603a094ffc2a1401c05
https://github.com/pablofdezalc/akaze/commit/db3dc22981e856ca8111f2f7fe57d9c2e0286efc