How to fill contour line using opencv?

Question

for example, this rectangle center is hole. (white each pixel value = 255, black value = 0)

but, I want to fill this hole. (like picture below)

how to fill hole by rectangle using OpenCV.

This is called region filling, if you are on matlab then this might help you: http://www.mathworks.com/matlabcentral/answers/111131-how-to-fill-the-region-of-interest-by-white-color — mumair, Nov 11 '15 at 07:29
same problem answered here: http://stackoverflow.com/questions/1716274/fill-the-holes-in-opencv — mumair, Nov 11 '15 at 07:30

score 4 · Accepted Answer · answered Nov 11 '15 at 07:42

First find its convex hull, then fill in the inner region of it:

cv::Mat inputImage = cv::imread("input.jpg", CV_LOAD_IMAGE_GRAYSCALE);
cv::threshold(inputImage, inputImage, 10, 255, 0);

// find non-zero elements
cv::Mat nonZeroCoordinates;
cv::findNonZero(inputImage, nonZeroCoordinates);

cv::vector<cv::Point> points;
for (int i = 0; i < nonZeroCoordinates.total(); i++)
{
    points.push_back(nonZeroCoordinates.at<cv::Point>(i));
}

// Find convex hull
std::vector<int> hull;
cv::convexHull(cv::Mat(points), hull, false);

cv::vector<cv::Point> hullpoints;
int hullcount = (int)hull.size();

for (int i = 0; i < hullcount; i++)
{
    cv::Point pt = points[hull[i]];
    hullpoints.push_back(pt);
}

std::vector<std::vector<cv::Point> > fillContAll;
fillContAll.push_back(hullpoints);

cv::Mat result = cv::Mat::zeros(inputImage.size(), CV_8UC1);
cv::fillPoly(result, fillContAll, cv::Scalar(255));

Given your original image:

This is your final result:

How to fill contour line using opencv?

1 Answers1