OpenCV closing a shape and filling it

Og Namdik picture Og Namdik · Oct 17, 2012 · Viewed 25.2k times · Source

I want to output a blue-filled hand but get the incorrect output. I've included the input picture, incorrect output picture and code below.

i think the code below does not fill the whole image because the image isn't closed yet at the right boundary.

how do i close the shape and fill it with blue properly?

close shape

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace cv;
using namespace std;

void drawStuff();
void showInputWindow();
void showCannyWindow();
void showContourWindow();

int thresh = 40;
int max_thresh = 120;
Mat img_rgb,img_gray,img_bw,canny_output,drawing;

int main(){
    img_rgb  = imread("qq.jpg");
    blur( img_rgb, img_rgb, Size(3,3) );
    cvtColor(img_rgb,img_gray,CV_RGB2GRAY);
    showInputWindow();

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

void drawStuff(){
    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;

    Canny( img_gray, canny_output, thresh, thresh*2, 3 );
    cv::dilate(canny_output, canny_output, cv::Mat(), cv::Point(-1,-1));
    showCannyWindow();

    findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
    drawing = Mat::zeros( canny_output.size(), CV_8UC3 );

    vector<Point> approxShape;
    for(size_t i = 0; i < contours.size(); i++){
        approxPolyDP(contours[i], approxShape, arcLength(Mat(contours[i]), true)*0.04, true);
        drawContours(drawing, contours, i, Scalar(255, 0, 0), CV_FILLED);   // fill BLUE
    }

    showContourWindow();
}

void showInputWindow(){
    cv::namedWindow("InputImage");
    cv::imshow("InputImage",img_rgb);
}

void showCannyWindow(){
    cv::namedWindow("Canny");
    cv::imshow("Canny",canny_output);
}
void showContourWindow(){
    cv::namedWindow("Fill");
    cv::imshow("Fill",drawing);
}

Answer

Marek picture Marek · Aug 14, 2013

To solve your problem, you should detect only outer contours. By doing that you will get only one contour, and you can fill it with your color.

findContours( canny_output, contours, hierarchy, Imgproc.RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );