I use the wiki code to transform coordinates to NW-Side of a png-picture file.
What I don´t understand, how can I calc the NE, SW, SE side of the picture.

In code it says NE = x+1 / y .png
SW = X/Y+1 .png and so on.

But x+1 is also the NW of the next tile… So NE of one tile cannot be the same as NW of the next?
They doesn´t overlay, so I have to substract something (for 1 pixel) ?? …

I don’t get your question. Maybe try to draw a picture?

Numbers of a NE of a subtile has coordinates [2x+1, 2y]
Numbers of a NW of subtile of the next eastern tile is [2x, 2y]

So, if tile A has x coordinate of 4, his NE subtile would have x component of 9
If next tile B has x coordinate of 5, his NW subtile would have x component of 10