Adventure game systems usually use a special image (1bit) or several shapes (and you can only walk inside of those convex polygons).
You might want to take a look at AGS
It gets more complicated if you want that there are some foreground bits, which can be in front of the player. But again it can be solved with a 1bit image. "Extract" the regions where the foreground bit is set and draw em back to front while using the lower edge of em (and of the player) for determining the order.
If you want extra neat (correct) antialiasing you'll need seperate images, which need to be placed into the scene with some kind of editor.