{

public static partial class Operations

{

// assign greyscale value to each object

public static int[,] Label(int[,] image)

{

int[,] result = new int[image.GetLength(0), image.GetLength(1)];

Dictionary<Tuple<int, int>, List<Tuple<int, int>>> labels = Groups(image); // get objects

double step = 200.0 / labels.Count;

int i = 1;

foreach (List<Tuple<int, int>> set in labels.Values)

{

foreach (Tuple<int, int> p in set) // apply current label to object

result[p.Item1, p.Item2] = 50 + (int)(i * step);

i++;

}

return result;

}

// label from already computed objects

public static int[,] Label(Dictionary<Tuple<int, int>, List<Tuple<int, int>>> labels, int width, int height)

{

int[,] result = new int[width, height];

double step = 200.0 / labels.Count;

int i = 1;

foreach (List<Tuple<int, int>> set in labels.Values)

{

foreach (Tuple<int, int> p in set)

result[p.Item1, p.Item2] = 50 + (int)(i * step);

i++;

}

return result;

}

// find objects

public static Dictionary<Tuple<int, int>, List<Tuple<int, int>>> Groups(int[,] image)

{

// union find to store sets of all pixels in object

UnionFind<Tuple<int, int>> unionFind = new UnionFind<Tuple<int, int>>();

for (int x = 0; x < image.GetLength(0); x++)

for (int y = 0; y < image.GetLength(1); y++)

{

if (image[x, y] == 0)

continue;

Tuple<int, int> xy = new Tuple<int, int>(x, y);

unionFind.Make(xy);

if (x > 0)

unionFind.Union(xy, new Tuple<int, int>(x - 1, y));

if (y > 0)

unionFind.Union(xy, new Tuple<int, int>(x, y - 1));

}

// turns union find "inside out": (pixel->set identifier)->(set identifier->all pixels in set)

Dictionary<Tuple<int, int>, List<Tuple<int, int>>> labels = new Dictionary<Tuple<int, int>, List<Tuple<int, int>>>();

for (int x = 0; x < image.GetLength(0); x++)

for (int y = 0; y < image.GetLength(1); y++)

{

if (image[x, y] == 0)

continue;

Tuple<int, int> xy = new Tuple<int, int>(x, y), label = unionFind.Find(xy);

List<Tuple<int, int>> list;

if (!labels.TryGetValue(label, out list))

{

list = new List<Tuple<int, int>>();

labels[label] = list;

}

list.Add(xy);

}

return labels;

}

}

}