watershed.cpp

/**
 * Count and segment overlapping objects with Watershed and Distance Transform.
 *
 * See the tutorial at:
 * http://opencv-code.com/count-and-segment-overlapping-objects-with-watershed-and-distance-transform/
 */
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>

int main()
{
	cv::Mat src = cv::imread("coins.jpg");
	if (!src.data)
		return -1;

	cv::imshow("src", src);

	// Create binary image from source image
	cv::Mat bw;
	cv::cvtColor(src, bw, CV_BGR2GRAY);
	cv::threshold(bw, bw, 40, 255, CV_THRESH_BINARY);
	cv::imshow("bw", bw);

	// Perform the distance transform algorithm
	cv::Mat dist;
	cv::distanceTransform(bw, dist, CV_DIST_L2, 3);

	// Normalize the distance image for range = {0.0, 1.0}
	// so we can visualize and threshold it
	cv::normalize(dist, dist, 0, 1., cv::NORM_MINMAX);
	cv::imshow("dist", dist);

	// Threshold to obtain the peaks 
	// This will be the markers for the foreground objects
	cv::threshold(dist, dist, .5, 1., CV_THRESH_BINARY);
	cv::imshow("dist2", dist);

	// Create the CV_8U version of the distance image
	// It is needed for cv::findContours()
	cv::Mat dist_8u;
	dist.convertTo(dist_8u, CV_8U);

	// Find total markers
	std::vector<std::vector<cv::Point> > contours;
	cv::findContours(dist_8u, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
	int ncomp = contours.size();

	// Create the marker image for the watershed algorithm
	cv::Mat markers = cv::Mat::zeros(dist.size(), CV_32SC1);

	// Draw the foreground markers
	for (int i = 0; i < ncomp; i++)
		cv::drawContours(markers, contours, i, cv::Scalar::all(i+1), -1);

	// Draw the background marker
	cv::circle(markers, cv::Point(5,5), 3, CV_RGB(255,255,255), -1);
	cv::imshow("markers", markers*10000);

	// Perform the watershed algorithm
	cv::watershed(src, markers);

	// Generate random colors
	std::vector<cv::Vec3b> colors;
	for (int i = 0; i < ncomp; i++)
	{
		int b = cv::theRNG().uniform(0, 255);
		int g = cv::theRNG().uniform(0, 255);
		int r = cv::theRNG().uniform(0, 255);

		colors.push_back(cv::Vec3b((uchar)b, (uchar)g, (uchar)r));
	}

	// Create the result image
	cv::Mat dst = cv::Mat::zeros(markers.size(), CV_8UC3);

	// Fill labeled objects with random colors
	for (int i = 0; i < markers.rows; i++)
	{
		for (int j = 0; j < markers.cols; j++)
		{
			int index = markers.at<int>(i,j);
			if (index > 0 && index <= ncomp)
				dst.at<cv::Vec3b>(i,j) = colors[index-1];
			else
				dst.at<cv::Vec3b>(i,j) = cv::Vec3b(0,0,0);
		}
	}

	cv::imshow("dst", dst);

	cv::waitKey(0);
	return 0;
}