I apply watershed segmentation to detect touching objects and it works okay doing that. Now, I would like to draw contours of each object, so I can get their length, area, moments etc.. But the objects in the result of the segmentation are still touching. So, I fail to draw contours of each one. How can I draw contours of each object?
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
using namespace std;
using namespace cv;
int main()
{
Mat src = imread("source.png");
// Create binary image from source image
Mat srcGray;
cvtColor(src, srcGray, CV_BGR2GRAY);
Mat srcThresh;
threshold(srcGray, srcThresh, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);
// Perform the distance transform algorithm
Mat dist;
distanceTransform(srcThresh, dist, CV_DIST_L2, 3);
// Normalize the distance image for range = {0.0, 1.0}
normalize(dist, dist, 0, 1., NORM_MINMAX);
// Threshold to obtain the peaks
threshold(dist, dist, 0.1, 3.5, CV_THRESH_BINARY);
// Create the CV_8U version of the distance image
Mat dist_8u;
dist.convertTo(dist_8u, CV_8U);
// Find total markers
std::vector<std::vector<Point> > contours;
findContours(dist_8u, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
int ncomp = contours.size();
// Create the marker image for the watershed algorithm
Mat markers = Mat::zeros(dist.size(), CV_32SC1);
// Draw the foreground markers
for (int i = 0; i < ncomp; i++)
drawContours(markers, contours, i, Scalar::all(i + 1), -1);
// Draw the background marker
circle(markers, Point(5, 5), 3, CV_RGB(255, 255, 255), -1);
// Perform the watershed algorithm
watershed(src, markers);
Mat wgResult = (markers.clone()) * 10000;
imshow("Watershed", wgResult);
waitKey(0);
return 0;
}
The markers
matrix returned by watershed
contains the indices of the segmented regions, according to the seed. So each component will have the same seed value. You can then create a binary matrix for each seed like:
Mat1b mask = (markers == seed);
Once you have the binary mask for each component, you can easily compute its area, moments, etc...
Code:
#include <opencv2/opencv.hpp>
#include <iostream>
using namespace std;
using namespace cv;
int main()
{
Mat src = imread("D:\\SO\\img\\postit.png");
// Create binary image from source image
Mat srcGray;
cvtColor(src, srcGray, CV_BGR2GRAY);
Mat srcThresh;
threshold(srcGray, srcThresh, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);
// Perform the distance transform algorithm
Mat dist;
distanceTransform(srcThresh, dist, CV_DIST_L2, 3);
// Normalize the distance image for range = {0.0, 1.0}
normalize(dist, dist, 0, 1., NORM_MINMAX);
// Threshold to obtain the peaks
threshold(dist, dist, 0.1, 3.5, CV_THRESH_BINARY);
// Create the CV_8U version of the distance image
Mat dist_8u;
dist.convertTo(dist_8u, CV_8U);
// Find total markers
std::vector<std::vector<Point> > contours;
findContours(dist_8u, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
int ncomp = contours.size();
// Create the marker image for the watershed algorithm
Mat markers = Mat::zeros(dist.size(), CV_32SC1);
// Draw the foreground markers
for (int i = 0; i < ncomp; i++)
drawContours(markers, contours, i, Scalar::all(i + 1), -1);
// Draw the background marker
circle(markers, Point(5, 5), 3, CV_RGB(255, 255, 255), -1);
// Perform the watershed algorithm
watershed(src, markers);
for (int seed = 1; seed <= ncomp; ++seed)
{
Mat1b mask = (markers == seed);
// Now you have the mask, you can compute your statistics
imshow("Mask", mask);
waitKey();
}
return 0;
}