I'm using C# and Visual Studios 2010 with XNA 4.0+lua, and my teacher has asked us to make a 2D RPG game similar to zelda(top down). I was aiming to use just one image for each map region, instead of using the tile approach, however i'm stuck on the aspect of movement limitation.

My teacher mentioned being able to mask another image on top of the map's current image, using only back and white colors and using those to be able control where the avatar can move(move where black is and restrict movement where white is). He did not, however, instruct us on how to do this, and I have been unable to find any tutorials anywhere.

I'm fairly new to C# in general, so if anyone can point me in the direction of a tutorial that could help me accomplish this, or add their own advice I would really, greatly appreciate it.