Can you explain how do you create a map.txt file?

[Mustafa-Agha]

..........................
..........................
..oo..oo..oo..oo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..ooQQoo..oo..oo..
..oo..oo..ooQQoo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..........oo..oo..
..oo..oo..........oo..oo..
..........oo..oo..........
..........oo..oo..........
oo..oooo..........oooo..oo
QQ..oooo..........oooo..QQ
..........oo..oo..........
..........oooooo..........
..oo..oo..oooooo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..oo..oo..oo..oo..
..oo..oo..........oo..oo..
..oo..oo..........oo..oo..
..oo..oo...oooo...oo..oo..
...........o..o...........
...........o..o...........

This is converted by this method

private void GenerateObjects(string[] m)
    {
        for (int i = 0; i < 26; i++)
        {
            for (int j = 0; j < 26; j++)
            {
                Transform t = null;
                if (m[i][j] == 'o')
                {
                    t = Instantiate(wall, new Vector3(j - 13, 13 - (i + 1), 0), wall.rotation) as Transform;
                }
                else if (m[i][j] == 'Q')
                {
                    t = Instantiate(iron, new Vector3(j - 13, 13 - (i + 1), 0), wall.rotation) as Transform;
                }
                else if (m[i][j] == 'b')
                {
                    t = Instantiate(bush, new Vector3(j - 13, 13 - (i + 1), 0), wall.rotation) as Transform;
                }
                else if (m[i][j] == 'i')
                {
                    t = Instantiate(ice, new Vector3(j - 13, 13 - (i + 1), 0), wall.rotation) as Transform;
                }
                else if (m[i][j] == 'w')
                {
                    t = Instantiate(water, new Vector3(j - 13, 13 - (i + 1), 0), wall.rotation) as Transform;
                }
                if (m[i][j] != '.')
                {
                    t.parent = generatedWallFolder;
                }
            }
        }
    }

Can you make a tool to convert specific png to this map.txt file?

I'm thinking of something like convert the png image to 26x26 (416x416 == 16x16) and read each block based on color
If the color is black then we add . if white then we add Q and so on..
I think this will work.