Flood-fill Demo


Click on the image to set seed point. This example imitates the fill colour functionality of the MS Windows Paint program.

Usage:

Keys to handle the GUI functions:

  • f - toggle floating range
  • c - toggle 4/8 connectivity
  • ESC - exit

I used the following sample image and coloured it using the following script. The script outputs a GUI containing trackbars to choose the RGB value and also to set the resolution. You have to click on a portion in the image to 'floodfill' it with a colour corresponding to the chosen RGB value.

In [ ]:
#!/usr/bin/env python
# Python 2/3 compatibility
from __future__ import print_function

import numpy as np
import cv2

if __name__ == '__main__':
    import sys
    
    fn = 'floodfillshapes.png'
    img = cv2.imread(fn, True)
    if img is None:
        print('Failed to load image file:', fn)
        sys.exit(1)

    h, w = img.shape[:2]
    mask = np.zeros((h+2, w+2), np.uint8)
    seed_pt = None
    fixed_range = True
    connectivity = 4

    def update(dummy=None):
        if seed_pt is None:
            cv2.imshow('floodfill', img)
            return
        flooded = img.copy()
        mask[:] = 0

        # get current positions of trackbars
        r = cv2.getTrackbarPos('R','floodfill')
        g = cv2.getTrackbarPos('G','floodfill')
        b = cv2.getTrackbarPos('B','floodfill')
        
        lo = cv2.getTrackbarPos('lo', 'floodfill')
        hi = cv2.getTrackbarPos('hi', 'floodfill')
        flags = connectivity
        if fixed_range:
            flags |= cv2.FLOODFILL_FIXED_RANGE
        cv2.floodFill(flooded, mask, seed_pt, (b, g, r), (lo,)*3, (hi,)*3, flags)
        cv2.circle(flooded, seed_pt, 2, (0, 0, 255), -1)
        cv2.imshow('floodfill', flooded)

    def onmouse(event, x, y, flags, param):
        global seed_pt
        if flags & cv2.EVENT_FLAG_LBUTTON:
            seed_pt = x, y
            update()

    update()
    cv2.setMouseCallback('floodfill', onmouse)

    cv2.createTrackbar('R','floodfill',0,255,update)
    cv2.createTrackbar('G','floodfill',0,255,update)
    cv2.createTrackbar('B','floodfill',0,255,update)

    cv2.createTrackbar('lo', 'floodfill', 20, 255, update)
    cv2.createTrackbar('hi', 'floodfill', 20, 255, update)

    while True:
        ch = 0xFF & cv2.waitKey()
        if ch == 27:
            break
        if ch == ord('f'):
            fixed_range = not fixed_range
            print('using %s range' % ('floating', 'fixed')[fixed_range])
            update()
        if ch == ord('c'):
            connectivity = 12-connectivity
            print('connectivity =', connectivity)
            update()
    cv2.destroyAllWindows()

The output looks like this :