How do I find the set of regions that are fully enclosed by a color?

Question

How do I get all areas surrounded by a certain color in a multidimensional array?

For example, this map has three regions that are fully enclosed by red tiles. They are highlighted enclosed in pink.

I'd want the algorithm to return three regions, with the positions of the tiles inside them.

How can I do this?

Answer 1

I would use this algorithm (in pseudocode):

iterate your whole playing field to create a list of all non-red tiles called LIST
while LIST has entries
    flood-fill from the first entry of LIST
    remove the results of the flood-fill from LIST
    if no result of the flood-fill is at the edge of the map
        add floodfill result to surrounded areas

Answer 2

If I understood what you are asking, for every non-red, border tile, flood red. At last the non-red tiles are surrounded by red.

In the example starting from top-left corner going anti-clockwise...