Flood fill Algorithm – how to implement fill() in paint?

In MS-Paint, when we take the brush to a pixel and click, the color of the region of that pixel is replaced with a new selected color. Following is the problem statement to do this task.
Given a 2D screen, location of a pixel in the screen and a color, replace color of the given pixel and all adjacent same colored pixels with the given color.

Example: 

Input:
       screen[M][N] = {{1, 1, 1, 1, 1, 1, 1, 1},
                      {1, 1, 1, 1, 1, 1, 0, 0},
                      {1, 0, 0, 1, 1, 0, 1, 1},
                      {1, 2, 2, 2, 2, 0, 1, 0},
                      {1, 1, 1, 2, 2, 0, 1, 0},
                      {1, 1, 1, 2, 2, 2, 2, 0},
                      {1, 1, 1, 1, 1, 2, 1, 1},
                      {1, 1, 1, 1, 1, 2, 2, 1},
                      };
    x = 4, y = 4, newColor = 3
The values in the given 2D screen indicate colors of the pixels.
x and y are coordinates of the brush, newColor is the color that
should replace the previous color on screen[x][y] and all surrounding
pixels with same color.

Output:
Screen should be changed to following.
       screen[M][N] = {{1, 1, 1, 1, 1, 1, 1, 1},
                      {1, 1, 1, 1, 1, 1, 0, 0},
                      {1, 0, 0, 1, 1, 0, 1, 1},
                      {1, 3, 3, 3, 3, 0, 1, 0},
                      {1, 1, 1, 3, 3, 0, 1, 0},
                      {1, 1, 1, 3, 3, 3, 3, 0},
                      {1, 1, 1, 1, 1, 3, 1, 1},
                      {1, 1, 1, 1, 1, 3, 3, 1},
                      };

Flood Fill Algorithm:
The idea is simple, we first replace the color of current pixel, then recur for 4 surrounding points. The following is detailed algorithm. 

// A recursive function to replace previous color 'prevC' at  '(x, y)' 
// and all surrounding pixels of (x, y) with new color 'newC' and
floodFil(screen[M][N], x, y, prevC, newC)
1) If x or y is outside the screen, then return.
2) If color of screen[x][y] is not same as prevC, then return
3) Recur for north, south, east and west.
    floodFillUtil(screen, x+1, y, prevC, newC);
    floodFillUtil(screen, x-1, y, prevC, newC);
    floodFillUtil(screen, x, y+1, prevC, newC);
    floodFillUtil(screen, x, y-1, prevC, newC);

The following is C++ implementation of above algorithm.

filter_none

edit
close

play_arrow

link
brightness_4
code

// A C++ program to implement flood fill algorithm
#include<iostream>
using namespace std;
  
// Dimentions of paint screen
#define M 8
#define N 8
  
// A recursive function to replace previous color 'prevC' at  '(x, y)' 
// and all surrounding pixels of (x, y) with new color 'newC' and
void floodFillUtil(int screen[][N], int x, int y, int prevC, int newC)
{
    // Base cases
    if (x < 0 || x >= M || y < 0 || y >= N)
        return;
    if (screen[x][y] != prevC)
        return;
  
    // Replace the color at (x, y)
    screen[x][y] = newC;
  
    // Recur for north, east, south and west
    floodFillUtil(screen, x+1, y, prevC, newC);
    floodFillUtil(screen, x-1, y, prevC, newC);
    floodFillUtil(screen, x, y+1, prevC, newC);
    floodFillUtil(screen, x, y-1, prevC, newC);
}
  
// It mainly finds the previous color on (x, y) and
// calls floodFillUtil()
void floodFill(int screen[][N], int x, int y, int newC)
{
    int prevC = screen[x][y];
    floodFillUtil(screen, x, y, prevC, newC);
}
  
// Driver program to test above function
int main()
{
    int screen[M][N] = {{1, 1, 1, 1, 1, 1, 1, 1},
                      {1, 1, 1, 1, 1, 1, 0, 0},
                      {1, 0, 0, 1, 1, 0, 1, 1},
                      {1, 2, 2, 2, 2, 0, 1, 0},
                      {1, 1, 1, 2, 2, 0, 1, 0},
                      {1, 1, 1, 2, 2, 2, 2, 0},
                      {1, 1, 1, 1, 1, 2, 1, 1},
                      {1, 1, 1, 1, 1, 2, 2, 1},
                     };
    int x = 4, y = 4, newC = 3;
    floodFill(screen, x, y, newC);
  
    cout << "Updated screen after call to floodFill: n";
    for (int i=0; i<M; i++)
    {
        for (int j=0; j<N; j++)
           cout << screen[i][j] << " ";
        cout << endl;
    }
}

chevron_right






                        filter_none








Output: 


Updated screen after call to floodFill:
1 1 1 1 1 1 1 1
1 1 1 1 1 1 0 0
1 0 0 1 1 0 1 1
1 3 3 3 3 0 1 0
1 1 1 3 3 0 1 0
1 1 1 3 3 3 3 0
1 1 1 1 1 3 1 1
1 1 1 1 1 3 3 1


References:

http://en.wikipedia.org/wiki/Flood_fill


This article is contributed by Anmol. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



          
          
          
          

            

    

        My Personal Notes
        arrow_drop_up
    

    

        
        

            
            
        

    


Recommended Posts: