Splitting tiles is a very easy way of creating doors by using already existent art. You can also dissect various objects and reassemble them to create brand new and unique art.
First, open up your !Door3.png file. This will serve as your template.
Second, return to your TileA4.png and select the last wall to the right in the middle row by using the Marquee Tool (press “M"):
Third, copy the selection (CTRL+C) and paste it on your !Door3.png file. If you want to, you can change the door’s color (I did).
Fourth, try to position your wall above the one of the doors. You’ll notice the wall is too big. No big deal. Select “Edit", followed by “Free Transform".
Now resize the wall so that it’s about the same size as your door.
Fifth, all you need now is to decide how you’d like your door to look like when they open. This is really a question of choice but I’ll show you the way I did it.
By using “Edit", followed by “Rotate Counter Clockwise", I shifted the wall horizontally.
Then I corrected the darker patch on the wall (what used to be the bottom of the wall) so that it looks similar to the other side by using the “Dodge Tool" (press "O" on your keyboard).
Fifth, by selecting the move tool (“V") and by holding down ALT, I made two more copies of my door right underneath the first one.
All I had left to do was to modify the last two pictures to make it look like the door was opening. This can be done by using the Marquee tool (“M") first and then moving both sides of the door with the move tool (“V").
Here’s the final result:
Import your !Door3.png graphic file into the game and add the door to your map. In the end, it should look something like this: