OpenCV C ++ / Obj-C: Connect adjacent contours

Question

Is there a function to connect two (or more) nearest circuits? Take a look at my I / O and you will see what I mean ...

My code is:

[... some processing ...]

// getting contours
std::vector<std::vector<cv::Point> > contours;
findContours(input, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);

// approximate contours
std::vector<std::vector<cv::Point> > contours_poly( contours.size() );
for( int i = 0; i < contours.size(); i++ ) {
  approxPolyDP(cv::Mat(contours[i]), contours_poly[i], 5, true );
}

// debugging
cv::Scalar colors[3];
colors[0] = cv::Scalar(255, 0, 0);
colors[1] = cv::Scalar(0, 255, 0);
colors[2] = cv::Scalar(0, 0, 255);
for (int idx = 0; idx < contours_poly.size(); idx++) {
  cv::drawContours(output, contours_poly, idx, colors[idx % 3]);
} 

Answer 1

I came up with this solution because I just need a bounding box around the whole object:

[... some processing ...]

// getting contours
std::vector<std::vector<cv::Point> > contours;
findContours(input, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);

// approximate contours
std::vector<std::vector<cv::Point> > contours_poly( contours.size() );
for( int i = 0; i < contours.size(); i++ ) {
  approxPolyDP(cv::Mat(contours[i]), contours_poly[i], 5, true );
}

// merge all contours into one vector
std::vector<cv::Point> merged_contour_points;
for (int i = 0; i < contours_poly.size(); i++) {
  for (int j = 0; j < contours_poly[i].size(); j++) {
    merged_contour_points.push_back(contours_poly[i][j]);
  }
}

// get rotated bounding box
std::vector<cv::Point> hull;
cv::convexHull(cv::Mat(merged_contour_points),hull);
cv::Mat hull_points(hull);
cv::RotatedRect rotated_bounding_rect = minAreaRect(hull_points);

Sometimes removing pepper noises can lead to better results:

void removePepperNoise(cv::Mat &mask)
{
    for ( int y=2; y<mask.rows-2; y++ ) {
        uchar *pUp2 = mask.ptr(y-2);
        uchar *pUp1 = mask.ptr(y-1);
        uchar *pThis = mask.ptr(y);
        uchar *pDown1 = mask.ptr(y+1);
        uchar *pDown2 = mask.ptr(y+2);
        pThis += 2;
        pUp1 += 2;
        pUp2 += 2;
        pDown1 += 2;
        pDown2 += 2;

        for (int x=2; x<mask.cols-2; x++) {
            uchar value = *pThis; // Get this pixel value (0 or 255). // Check if this is a black pixel that is surrounded by white pixels
            if (value == 0) {
                bool above, left, below, right, surroundings;
                above = *(pUp2 - 2) && *(pUp2 - 1) && *(pUp2) && *(pUp2 + 1) && *(pUp2 + 2);
                left = *(pUp1 - 2) && *(pThis - 2) && *(pDown1 - 2);
                below = *(pDown2 - 2) && *(pDown2 - 1) && *(pDown2) && *(pDown2 + 1) && *(pDown2 + 2);
                right = *(pUp1 + 2) && *(pThis + 2) && *(pDown1 + 2);
                surroundings = above && left && below && right;
                if (surroundings == true) {
                    // Fill the whole 5x5 block as white. Since we know
                    // the 5x5 borders are already white, we just need to
                    // fill the 3x3 inner region.
                    *(pUp1 - 1) = 255;
                    *(pUp1 + 0) = 255;
                    *(pUp1 + 1) = 255;
                    *(pThis - 1) = 255;
                    *(pThis + 0) = 255;
                    *(pThis + 1) = 255;
                    *(pDown1 - 1) = 255;
                    *(pDown1 + 0) = 255;
                    *(pDown1 + 1) = 255;
                    // Since we just covered the whole 5x5 block with
                    // white, we know the next 2 pixels won't be black,
                    // so skip the next 2 pixels on the right.
                    pThis += 2;
                    pUp1 += 2;
                    pUp2 += 2;
                    pDown1 += 2;
                    pDown2 += 2;
                }
            }
            // Move to the next pixel on the right.
            pThis++;
            pUp1++;
            pUp2++;
            pDown1++;
            pDown2++;
        }
    }
}

Answer 2

Just go through the points and find the nearest starting point or end points, and then connect them. It is difficult to decide in your case if the contours should be connected or not. If morphology, as Adrian Popovich said, does not help you indicate some maximum distance, which decides whether the points should be connected.