watershed algorithm to image with grey background

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this example program demonstrates using watershed

but you need some preprocessing like below ( add this piece of code to imageSegmentation.cpp line 26)

Mat img_gray;
cvtColor(src, img_gray, cv::COLOR_BGR2HSV);

Mat hsv[3];
split(img_gray, hsv);

img_gray = hsv[2] + hsv[1];
imshow("img_gray", img_gray);
src.setTo(Scalar(0, 0, 0), ~img_gray);
    // ( this code is suitable for bright objects on gray background )

this step will give you the image below

and you will finally get the image below.