samples/cpp/snippets/watershed.cpp

An example using the watershed algorithm

#include <opencv2/core/utility.hpp>
#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
 
#include <cstdio>
#include <iostream>
 
using namespace cv;
using namespace std;
 
static void help(char** argv)
{
    cout << "\nThis program demonstrates the famous watershed segmentation algorithm in OpenCV: watershed()\n"
            "Usage:\n" << argv[0] <<" [image_name -- default is fruits.jpg]\n" << endl;
 
 
    cout << "Hot keys: \n"
        "\tESC - quit the program\n"
        "\tr - restore the original image\n"
        "\tw or SPACE - run watershed segmentation algorithm\n"
        "\t\t(before running it, *roughly* mark the areas to segment on the image)\n"
        "\t  (before that, roughly outline several markers on the image)\n";
}
Mat markerMask, img;
Point prevPt(-1, -1);
 
static void onMouse( int event, int x, int y, int flags, void* )
{
    if( x < 0 || x >= img.cols || y < 0 || y >= img.rows )
        return;
    if( event == EVENT_LBUTTONUP || !(flags & EVENT_FLAG_LBUTTON) )
        prevPt = Point(-1,-1);
    else if( event == EVENT_LBUTTONDOWN )
        prevPt = Point(x,y);
    else if( event == EVENT_MOUSEMOVE && (flags & EVENT_FLAG_LBUTTON) )
    {
        Point pt(x, y);
        if( prevPt.x < 0 )
            prevPt = pt;
        line( markerMask, prevPt, pt, Scalar::all(255), 5, 8, 0 );
        line( img, prevPt, pt, Scalar::all(255), 5, 8, 0 );
        prevPt = pt;
        imshow("image", img);
    }
}
 
int main( int argc, char** argv )
{
    cv::CommandLineParser parser(argc, argv, "{help h | | }{ @input | fruits.jpg | }");
    if (parser.has("help"))
    {
        help(argv);
        return 0;
    }
    string filename = samples::findFile(parser.get<string>("@input"));
    Mat img0 = imread(filename, IMREAD_COLOR), imgGray;
 
    if( img0.empty() )
    {
        cout << "Couldn't open image ";
        help(argv);
        return 0;
    }
    help(argv);
    namedWindow( "image", 1 );
 
    img0.copyTo(img);
    cvtColor(img, markerMask, COLOR_BGR2GRAY);
    cvtColor(markerMask, imgGray, COLOR_GRAY2BGR);
    markerMask = Scalar::all(0);
    imshow( "image", img );
    setMouseCallback( "image", onMouse, 0 );
 
    for(;;)
    {
        char c = (char)waitKey(0);
 
        if( c == 27 )
            break;
 
        if( c == 'r' )
        {
            markerMask = Scalar::all(0);
            img0.copyTo(img);
            imshow( "image", img );
        }
 
        if( c == 'w' || c == ' ' )
        {
            int i, j, compCount = 0;
            vector<vector<Point> > contours;
            vector<Vec4i> hierarchy;
 
            findContours(markerMask, contours, hierarchy, RETR_CCOMP, CHAIN_APPROX_SIMPLE);
 
            if( contours.empty() )
                continue;
            Mat markers(markerMask.size(), CV_32S);
            markers = Scalar::all(0);
            int idx = 0;
            for( ; idx >= 0; idx = hierarchy[idx][0], compCount++ )
                drawContours(markers, contours, idx, Scalar::all(compCount+1), -1, 8, hierarchy, INT_MAX);
 
            if( compCount == 0 )
                continue;
 
            vector<Vec3b> colorTab;
            for( i = 0; i < compCount; i++ )
            {
                int b = theRNG().uniform(0, 255);
                int g = theRNG().uniform(0, 255);
                int r = theRNG().uniform(0, 255);
 
                colorTab.push_back(Vec3b((uchar)b, (uchar)g, (uchar)r));
            }
 
            double t = (double)getTickCount();
            watershed( img0, markers );
            t = (double)getTickCount() - t;
            printf( "execution time = %gms\n", t*1000./getTickFrequency() );
 
            Mat wshed(markers.size(), CV_8UC3);
 
            // paint the watershed image
            for( i = 0; i < markers.rows; i++ )
                for( j = 0; j < markers.cols; j++ )
                {
                    int index = markers.at<int>(i,j);
                    if( index == -1 )
                        wshed.at<Vec3b>(i,j) = Vec3b(255,255,255);
                    else if( index <= 0 || index > compCount )
                        wshed.at<Vec3b>(i,j) = Vec3b(0,0,0);
                    else
                        wshed.at<Vec3b>(i,j) = colorTab[index - 1];
                }
 
            wshed = wshed*0.5 + imgGray*0.5;
            imshow( "watershed transform", wshed );
        }
    }
 
    return 0;
}