I think it is a bit hard to do some simple tasks on this software, and one of them is to turn a simple image into tile map. The software forces you to have the image with a height and width that are multiples of the height and width of the tile size selected. That is a situation that could be perfectly handled by the software, by its own, and not to transfer that extra task to the user. If you see how PyxelEdit handles that same situation for example, it is a lot easier.