/// <summary>
/// Selects a guessed background of the input image
/// </summary>
/// <param name="input">The input image</param>
/// <param name="token">The cancellation token</param>
/// <remarks>Performs a BFS</remarks>
/// <returns>Returns the list of pixels having the same color as the color of the guessed background, null when cancellation was requested</returns>
private List <int> SelectBackground(PPImage input, CancellationToken token = default)
{
SKColor bgColor = SKColors.Transparent;
Dictionary <SKColor, List <int> > components = new Dictionary <SKColor, List <int> >();
int[] cornerIndices = new int[] { 0, //top-left
input.Bitmap.Width - 1, //top-right
(input.Bitmap.Height - 1) * input.Bitmap.Width, //bottom-left
input.Bitmap.Width *input.Bitmap.Height - 1 }; //bottom-right};
var pixels = input.Bitmap.Pixels;
SKColor[] cornerColors = new SKColor[4]
{
pixels[cornerIndices[0]],
pixels[cornerIndices[1]],
pixels[cornerIndices[2]],
pixels[cornerIndices[3]]
};
bool[] visited = new bool[input.Bitmap.Width * input.Bitmap.Height];
Dictionary <SKColor, float> colorCounts = new Dictionary <SKColor, float>();
Queue <int> toVisit = new Queue <int>();
foreach (var corner in cornerIndices)
{
if (token.IsCancellationRequested)
{
return(null);
}
toVisit.Enqueue(corner);
visited[corner] = true;
}
if (cornerColors.All(x => x == cornerColors[0]))
{
colorCounts.Add(cornerColors[0], 0.0f);
components.Add(cornerColors[0], new List <int>());
int totalVisited = 0;
while (toVisit.Count > 0)
{
if (token.IsCancellationRequested)
{
return(null);
}
var curr = toVisit.Dequeue();
totalVisited++;
foreach (var neigh in GetNeighborhood(curr, input).Where(x => x != curr && x >= 0 && x < input.Bitmap.Width * input.Bitmap.Height))
{
if (visited[neigh] || pixels[neigh] != cornerColors[0])
{
continue;
}
toVisit.Enqueue(neigh);
visited[neigh] = true;
}
if (pixels[curr] == cornerColors[0])
{
components[cornerColors[0]].Add(curr);
colorCounts[cornerColors[0]] += 1.0f;
}
}
return(components[cornerColors[0]]);
}
else
{
var uniqueColors = cornerColors.Distinct();
foreach (var x in uniqueColors)
{
components.Add(x, new List <int>());
colorCounts.Add(x, 0.0f);
}
while (toVisit.Count > 0)
{
if (token.IsCancellationRequested)
{
return(null);
}
var curr = toVisit.Dequeue();
foreach (var neigh in GetNeighborhood(curr, input).Where(z => z != curr && z >= 0 && z < input.Bitmap.Width * input.Bitmap.Height))
{
if (visited[neigh] || !cornerColors.Contains(pixels[neigh]))
{
continue;
}
toVisit.Enqueue(neigh);
visited[neigh] = true;
}
//if (uniqueColors.Contains(input.Pixels[curr]))
//{
components[pixels[curr]].Add(curr);
float x = curr % input.Bitmap.Width;
float y = curr / input.Bitmap.Width;
float middleX = input.Bitmap.Width / 2.0f;
float middleY = input.Bitmap.Height / 2.0f;
colorCounts[pixels[curr]] += Max(Abs(middleX - x), Abs(middleY - y));
//colorCounts[input.Pixels[curr]] += 1.0f;
//}
visited[curr] = true;
}
bgColor = colorCounts.OrderByDescending(x => x.Value).First().Key;
return(components[bgColor]);
}
//return bgColor;
}