Task: Bitmap_Flood fill
C#: using System;
using System.Collections.Generic;
using System.Drawing;

namespace FloodFill
{
    class Program
    {
        private static bool ColorMatch(Color a, Color b)
        {
            return (a.ToArgb() & 0xffffff) == (b.ToArgb() & 0xffffff);
        }

        static void FloodFill(Bitmap bmp, Point pt, Color targetColor, Color replacementColor)
        {
            Queue<Point> q = new Queue<Point>();
            q.Enqueue(pt);
            while (q.Count > 0)
            {
                Point n = q.Dequeue();
                if (!ColorMatch(bmp.GetPixel(n.X, n.Y),targetColor))
                    continue;
                Point w = n, e = new Point(n.X + 1, n.Y);
                while ((w.X >= 0) && ColorMatch(bmp.GetPixel(w.X, w.Y),targetColor))
                {
                    bmp.SetPixel(w.X, w.Y, replacementColor);
                    if ((w.Y > 0) && ColorMatch(bmp.GetPixel(w.X, w.Y - 1),targetColor))
                        q.Enqueue(new Point(w.X, w.Y - 1));
                    if ((w.Y < bmp.Height - 1) && ColorMatch(bmp.GetPixel(w.X, w.Y + 1),targetColor))
                        q.Enqueue(new Point(w.X, w.Y + 1));
                    w.X--;
                }
                while ((e.X <= bmp.Width - 1) && ColorMatch(bmp.GetPixel(e.X, e.Y),targetColor))
                {
                    bmp.SetPixel(e.X, e.Y, replacementColor);
                    if ((e.Y > 0) && ColorMatch(bmp.GetPixel(e.X, e.Y - 1), targetColor))
                        q.Enqueue(new Point(e.X, e.Y - 1));
                    if ((e.Y < bmp.Height - 1) && ColorMatch(bmp.GetPixel(e.X, e.Y + 1), targetColor))
                        q.Enqueue(new Point(e.X, e.Y + 1));
                    e.X++;
                }
            }
        }

        static void Main(string[] args)
        {
            Bitmap bmp = new Bitmap("Unfilledcirc.bmp");
            FloodFill(bmp, new Point(200, 200), Color.White, Color.Red);
            FloodFill(bmp, new Point(100, 100), Color.Black, Color.Blue);
            bmp.Save("Filledcirc.bmp");
        }
    }
}

Java: import java.awt.Color;
import java.awt.Point;
import java.awt.image.BufferedImage;
import java.util.Deque;
import java.util.LinkedList;

public class FloodFill {
  public void floodFill(BufferedImage image, Point node, Color targetColor, Color replacementColor) {
    int width = image.getWidth();
    int height = image.getHeight();
    int target = targetColor.getRGB();
    int replacement = replacementColor.getRGB();
    if (target != replacement) {
      Deque<Point> queue = new LinkedList<Point>();
      do {
        int x = node.x;
        int y = node.y;
        while (x > 0 && image.getRGB(x - 1, y) == target) {
          x--;
        }
        boolean spanUp = false;
        boolean spanDown = false;
        while (x < width && image.getRGB(x, y) == target) {
          image.setRGB(x, y, replacement);
          if (!spanUp && y > 0 && image.getRGB(x, y - 1) == target) {
            queue.add(new Point(x, y - 1));
            spanUp = true;
          } else if (spanUp && y > 0 && image.getRGB(x, y - 1) != target) {
            spanUp = false;
          }
          if (!spanDown && y < height - 1 && image.getRGB(x, y + 1) == target) {
            queue.add(new Point(x, y + 1));
            spanDown = true;
          } else if (spanDown && y < height - 1 && image.getRGB(x, y + 1) != target) {
            spanDown = false;
          }
          x++;
        }
      } while ((node = queue.pollFirst()) != null);
    }
  }
}