New flipping code causes dead zones

[onitake]

Commit f715b99 causes dead zones for some users (see the commit comment from @barni2000.

If x_max and/or y_max is too small, negative coordinates can occur. I thought this was going to be a problem with the input layer, but apparently it's not.

Reverting the commit for now, I hope introducing x_min and y_min parameters will be a better fix.