OpenCV - How to use floodFill with RGB image?

Hadi GhahremanNezhad :

I am trying to use floodFill on an image like below to extract the sky:

But even when I set the loDiff=Scalar(0,0,0) and upDiff=Scalar(255,255,255) the result is just showing the seed point and does not grow larger (the green dot):

code:

Mat flood;
Point seed = Point(180, 80);
flood = imread("D:/Project/data/1.jpeg");
cv::floodFill(flood, seed, Scalar(0, 0, 255), NULL, Scalar(0, 0, 0), Scalar(255, 255, 255));
circle(flood, seed, 2, Scalar(0, 255, 0), CV_FILLED, CV_AA);

This is the result (red dot is the seed):

How can I set the function to get a larger area (like the whole sky)?

Rotem :

You need to set loDiff and upDiff arguments correctly.

See floodFill documentation:

loDiff – Maximal lower brightness/color difference between the currently observed pixel and one of its neighbors belonging to the component, or a seed pixel being added to the component.
upDiff – Maximal upper brightness/color difference between the currently observed pixel and one of its neighbors belonging to the component, or a seed pixel being added to the component.

Here is a Python code sample:

import cv2
flood = cv2.imread("1.jpeg");

seed = (180, 80)

cv2.floodFill(flood, None, seedPoint=seed, newVal=(0, 0, 255), loDiff=(5, 5, 5, 5), upDiff=(5, 5, 5, 5))
cv2.circle(flood, seed, 2, (0, 255, 0), cv2.FILLED, cv2.LINE_AA);

cv2.imshow('flood', flood)
cv2.waitKey(0)
cv2.destroyAllWindows()

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Result: